Integrated Circuit Board

The use of integrated circuits is very interesting, especially when it comes to programmable integrated circuits because of the endless possibilities that a microcontroller can offer. The possible combination and advantages of programmable integrated circuits are only limited to the designer capability. However, intermittent interchange of ICs between the prototype base and the programming board when playing microcontrollers can lead to incontinence and a slight reduction of the interesting part.

As a solution, a number of IC development boards existed which combine prototype and programming together to make it a single unit. Most IC development boards use USB as the primary power supply and programming port. Therefore, no additional power conditioning circuit and programming interface are required to allow the project to proceed. Almost no boards are made as per industry standards with high-end processors and common interfaces that can be used directly for practical applications. However, IC development board has the necessary components to connect boards to various modules and gadgets that are commonly available on the market. Development PCB board mainly uses SMD components to make it compact.

The PCB is made to fit various shields that can be used to further extend the functionality of the development board. The traditional IC development board has small versions which cover almost all of its features and can be installed anywhere in the project. Some advanced boards like raspberry pi can run on an independent operating system which can be used as a microcomputer system with some basic computer functionalities.

PCB Solder Mask

The printed circuit board uses copper as the main conductive path. Since copper has the high probability of reacting with the atmosphere and producing oxides, the conductivity reduces and the PCB performance will be destroyed. Also during the soldering process, the liquid solder may flow and form a solder bridge commonly referred to as two closed traces and lead to short circuit interconnection. To protect the copper from oxidation and to avoid soldering bridges, a thin coating is applied to the traces commonly referred to as solder mask.

There are few types when choosing solder mask. Depending upon the need and cost, appropriate solder mask is selected.

EpoxyEpoxy is a basic and cheap solder mask which is mainly used in low precision and prototyping PCBs. Since epoxy is semi solid in nature, it is usually applied through the silkscreen printing.

DFSM

DFSMs are like dry film photo resists used in copper etching. Prepared PCBs are vacuumed pressed with the sheet of DFSM. The solder pad is eliminated by covering the corresponding area with an anti-UV developer. The settings were then exposed to UV light to cure the DFSM. After a few minutes of exposure, the solder mask is transferred from the sheet to the PCB. The photoresist is then removed with a solvent.

LPSM

This is a liquid solder mask much like an ink which can be spray painted or immersed on a marked laminate. The solder cutouts are done by placing a temporary ink marks which is removed after the solder mask application. The applied PCB are exposed to UV light to dry out the ink. The dried PCBs are cleaned and re-inserted in to the exposure for a final cure.

3 Factors for Faulty PCB Soldering

Reviewing PCB board soldering technology development in the electronics industry, it can be noted that reflow technology has developed fast and stable. How to ensure the quality of PCB soldering is the major concern among electronics manufacturers, so in this article we outline three major reasons for faulty PCB board soldering.

Soldering quality is affected by the solderability of PCB board holePoor solderability of PCB board hole will make soldering defects, which can affect the parameter of circuit components, cause poor stable connection between components and inner layer in the multi-layer board, even worse, the entire circuit will be out of work. The so-called solderability is the property by melting the metal surface, that is, a relatively uniform continuous smooth film is formed by the solder on the solder surface.

Soldering defects caused by PCB warpage During the soldering process, PCB board and components may be warping due to the stress, and then short circuit, deformation and other defects may be caused. Warping is often caused by the imbalance temperature given to the upper and lower layers. Sometimes, large size of the PCB board may be warping due to its own weight. Distance from ordinary PBGA to the PCB board side is about 0.5mm. If components are larger on the board, then it is easily to cause faulty soldering when PCB board restore to its normal shape after cooling down. 

Soldering quality is affected by PCB designIf your board size is too large, the soldering is easy to control, but the printed line length and impedance will increase while the anti-noise ability will decrease, finally the cost will increase. If your board size is too small, the heat dissipation ability will decrease, the soldering is difficult to control, and adjacent lines tend to interfere with each other. Therefore, your PCB board design must be optimized.

Integrated Circuit Board

The use of integrated circuits is very interesting, especially when it comes to programmable integrated circuits because of the endless possibilities that a microcontroller can offer. The possible combination and advantages of programmable integrated circuits are only limited to the designer capability. However, intermittent interchange of ICs between the prototype base and the programming board when playing microcontrollers can lead to incontinence and a slight reduction of the interesting part.

As a solution, a number of IC development boards existed which combine prototype and programming together to make it a single unit. Most IC development boards use USB as the primary power supply and programming port. Therefore, no additional power conditioning circuit and programming interface are required to allow the project to proceed. Almost no boards are made as per industry standards with high-end processors and common interfaces that can be used directly for practical applications. However, IC development board has the necessary components to connect boards to various modules and gadgets that are commonly available on the market. Development PCB board mainly uses SMD components to make it compact.

The PCB is made to fit various shields that can be used to further extend the functionality of the development board. The traditional IC development board has small versions which cover almost all of its features and can be installed anywhere in the project. Some advanced boards like raspberry pi can run on an independent operating system which can be used as a microcomputer system with some basic computer functionalities.

Benefits of Flex and Rigid-Flex PCB

Flex PCB and rigid-flex PCB board allow you to design the circuitry to fit the device, instead of building a device to fit the circuit board. They are largely used in the industry of aerospace, medical and military applications thanks to dependable reliability.

Flex circuits offer multiple advantages, and the following will show you some key benefits of using flex and rigid-flex circuit technology.

Component/Connector Assembly1.Flex circuits can accept any component or connector that can be assembled to a rigid PCB design.2.Integrated ZIF contacts provide simple modular interfaces to the system environment.3.Additional options are available such as, ZIF Connectors, crimped contacts, direct solder to PCB, etc.

Cost Savings1.Thin and flexible polyimide film requires a much smaller area, reducing the overall finished assembly packaging size and material requirement costs.2.Reduced assembly costs are also seen as fewer parts are needed for the final assembled product.3.A simplified PCB assembly processes can reduce assembly errors as the flex circuit can only be installed one way.4.Flex circuits can eliminate wire routing errors, and reduce test time, rework, and rejects.

High Density Applications1.Flex material properties work very well in high speed controlled impedance designs, which allow better control of impedances.2.Flexible PCB allow for narrow lines giving way to high density device population. Denser device populations and lighter conductors can be designed into a product, freeing space for additional product features.

High Temperature Applications1.Flex circuits materials (polyimide) dissipate heat at a better rate than other dielectric materials while providing the added benefits of vastly improved flexibility.2.Exposed to extreme temperature applications (up to - 200C to 400C) is ok.3.Expansion and contraction are minimized when using polyimide material.4.Good chemical resistance to oils, acids, gases etc.5.Flex circuits boards offer excellent radiation and UV exposure resistance.

High Density Interconnect Board

High density interconnect board or HDI board is one of the fastest growing technologies in PCB industry. HDI boards contain blind and/or buried vias and often contain microvias of .006 or less in diameter. They have a higher circuitry density than traditional circuit boards.

There are 6 different types of HDI boards, through vias from surface to surface, with buried vias and through vias, two or more HDI layer with through vias, passive substrate with no electrical connection, coreless construction using layer pairs and alternate constructions of coreless constructions using layer pairs.

HDI technology is the leading reason for electronic products transformation like camera, mobile, computer, pad, etc. Products do more, weigh less and are physically smaller. Specialty equipment, mini-components and thinner materials have allowed for electronics to shrink in size while expanding technology, quality and speed.

As consumer demands change, so must technology. By using HDI technology, designers now have the option to place more components on both sides of the raw PCB. Decreased component size and pitch allow for more I/O in smaller geometries. This means faster transmission of signals and a significant reduction in signal loss and crossing delays.

While some consumer products shrink down in size, its quality remains at its best level. Using HDI technology is possible to reduce an 8 layer through-hole PCB to a 4 layer HDI microvia technology packed PCB. The wiring capabilities of a well-designed HDI 4 layer PCB can achieve the same or better functions as that of a standard 8 layer PCB. Although the microvia process increases the cost of the HDI PCB, the proper design and reduction in layer count reduces cost in material square inches and layer count more significantly.

A Flexible Circuit Coverlay

In the flexible printed circuit board manufacturing process, a flex circuit coverlay or coverfilm is used to protect the external circuitry of a flexible circuit board.

A flexible circuit coverlay serves the exact same function as soldermask that is used for rigid printed circuit boards. The difference with the flexible coverlay is the flexibility required for flexible circuit boards and the required components for durability.

The coverlay consists of a solid sheet of polyimide with a layer of flexible adhesive that is then laminated under heat and pressed to the circuit surfaces. The required component feature openings are mechanically created using drilling, routing, or laser cutting.

Typical coverlay thickness is 0.001" polyimide with 0.001" of adhesive. 0.0005" & 0.002" thicknesses are available, but only used as needed to meet specific design requirements. 

Polyimide coverlay and flexible liquid photoimageable (LPI) solder mask are two primary options for encapsulating the external circuit layers of a flex circuit board.

Of the two, polyimide coverlay is the most commonly used and preferred solution throughout the industry. It provides a much more robust and durable solution with very good flexibility and a high dielectric.

Flexible LPI solder mask is essentially the same formula that has the same capabilities and is applied in the same manner as on rigid circuit boards.

Tips for Flexible PCB Board Design

Before designing printed circuit boards, I almost unheard of flexible PCB board. But after several years’ experience, I have concluded sound design practice that is specific to flexible PCB is required to eliminate problems in fabrication and assembly. Here are some of them:

Avoid vias in bend areas-- Via should be avoided in bend as it can cause breakage on the flexible PCB when the stress applied goes beyond a threshold.

Clearance between components and flex area-- It is important to maintain a gap of at least 100mil for components and bend area. When placed on a bend area, the solder on the component’s pin became the weakest point as it is not meant to be bent.

Copper to edge clearance-- Like rigid PCB, you’re bound to have power and ground planes on Flexible PCB. It is important to have a decent clearance between the copper area and the edge of the flexible PCB. Neglecting this important guide could result in the copper shorting at the edges when the PCB is cut.

Ground plane design-- Cross hatch polygon is preferred for ground planes as it increased flexibility and reduce weight.Minimum hole size--Bear in mind that it is harder to drill on a flexible PCB than on a regular rigid PCB. Be sure to keep the hole size at a minimum of 10 mils for your design.

The IPC-2581 File Format

Eminent PCB manufacturers eliminate the problems by adopting design transfer standards that addresses all aspects of the fabrication and assembly process. Two new open standards are available, and these enable efficient and accurate data exchange from the PCB designer to the manufacturing fabricators and assemblers. Ucamco administers one of these standards, theGerber X2, while the IPC Consortium administers the other, the IPC-2581. Both are open standards, free from any proprietary restrictions.

Contributors from a wide range of PCB industry segment initiated, developed, and drove the IPC-2581 standard. The IPC-2581 is a single data format and within a single file, contains all aspects of the PCB design, such as layer stackup, materials, assembly, and test details.

With the IPC-2581 standard, the designer can include details of layer stack and information on materials to ensure proper layer order. The standard is suitable for stackups of complex board design such as related to rigid-flex boards, and is capable of handling special materials. It can also include drill and mill data for blind, buried, and filled via types. It also supports information on back drilling, V-grooves, slots, and cavities. For bare board testing, designers can include the net-list as well.

In addition to a complete set of fabrication data, the IPC-2581 can also hold assembly data. Therefore, it can contain not only the pick-and-place information, but also the information on polarity and rotation of a component, enabling support for both stacked and embedded components.

In addition to assembly drawings, the IPC-2581 standard has the capability to generate the documentation for bill of materials and purchasing. Therefore, the standard can tie up with PLM/ERP system data to create links between design and supply chain facilities. The greatest advantage of the IPC-2581 is one single file containing the entire data related to fabrication and assembly.

How does ESD Affect Your PCB Board?

Electrostatic discharge (ESD) occurs when two objects with different charges get close enough, or charged enough, to break down the dielectric between them. 

Any PCB may be subject to an ESD if it’s touched or comes close enough to people, packaging, cables, furry pets, or any other object that might contain an opposite charge. When they do touch, that voltage discharges and creates a comparatively massive voltage spike. As the voltage spike dissipates, the discharge current generates electromagnetic fields across the PCB. The goal of ESD protection is to minimize any impact or effects from the discharge.

In particular, many modern chipsets are made using such small lithography features that they have little or no tolerance for high voltage, even direct current values above their operating voltage of 3.3V. The result of an ESD event directly reaching one of these components is usually disastrous, completely ruining the integrated circuit.Nearly every element of your PCB design (traces, routing, layers, component placement, and spacing) can affect the ESD protection on your board. That means you need to consider ESD early in your design process; otherwise, you’re likely to require major PCB redesign to fix routing and component placement issues.

Why HASL and LFH are Concerned as a Hassle?

Hot air solder leveling, also known as HASL, has always been the major part of PCB surface finishes. As an excellent solderable finish for printed circuit boards, it has kept this surface finish alive in the market since late 80s. Given that PCBs are in everything from appliances to toys, it was almost instinct to find an alternative. Exposure of lead to children and overall health in general being a concern, getting lead out of products was the focal point of the electronic manufacturer.

It is obvious that lead may never be totally gone from all products, then the lead free version (LFH) existed. It became the most practice at surface finish next to immersion gold early on. So, why is lead free HASL still considered a hassle? 

The chemistry makeup of LFH has changed over the years as well as the applications. Vertical or horizontal applications both initially had the same issue as HASL, a pooling, non-flat finish with a somewhat foggy appearance in areas of the PCB.

Combinations of the LFH gave the finish a bad review. The combination of tin, silver, and copper alloy originally had poor results at the processing level, leaving behind a bumpy uneven coat that was dull and unattractive as well as having a poor performance in assembly. Removing the silver, changing the tin-copper, and tweaking the manufacturing process has allowed for a better smoother surface coating than originally found. 

Protect Your Ground Planes

For all the good a ground plane can do, it can also act as a direct path to your sensitive components if an ESD pulse discharges directly into it. To prevent this sort of damage, remember to use TVS circuits between the power and ground on sensitive components to divert the induced currents. When implemented correctly, the voltage differential experienced by components will be held to the clamping voltage of the TVS.

You can also use high-frequency bypass capacitors between power and ground on sensitive components. The capacitors will reduce the charge injection and voltage differences between power and ground. Keep those capacitors and your TVS close to the components you are worried about protecting.

Additionally, you should use a copper land when you are attaching connectors to your PCB. Make sure the land is separate from the PCB ground, or you just introduced a nice, low resistance path for ESD to reach all your components, even though you put all that other protection in place. And, in general, you should minimize path lengths whenever you can.

PCB Layout Tips

Hobbyists, students, even engineers tend to pay more attention to circuits, the latest components, and code as important parts of an electronics project, but sometimes neglect a critical component of electronics --- the PCB layout. As a Chinese saying goes, well begun is half done. Good PCB layout plays a great important role in your PCB projects, because poor PCB layout can cause function and reliability problems. 

Make Loops Small: Loops, especially high frequency loops, should be made as small as possible. Small loops have lower inductance and resistance. Placing them over a ground plane can further reduce inductance. Small loops also help reduce the amount of signals that are inductively coupled into the node from external sources, or are broadcast from the node. 

Decoupling Capacitor Placement: Place decoupling capacitors close enough to the power and ground pins of integrated circuits to maximize decoupling efficiency. Kelvin Connections: Kelvin connections are made at the exact points to reduce stray resistance and inductance. For example, Kelvin connections for a current sense resistor are placed exactly at the resistor pads. Placing the connections at the resistor pads may look the same on your layout, but real traces have inductance and resistance that could throw your measurements off if you don’t use Kelvin connections.

How to Choose Surface Finish

There are many surface finish types to choose when designing a printed circuit board. Do you know how to choose the best one for your electronics assemblies? EPCB lists some common but popular finishes with pros and cons for each.

Hot Air Solder Leveling    HASL has been around for many years. A thin layer of solder is mechanically applied to copper surfaces. A hot air knife is used to sheet the excess solder away to create a flat finish. It is cheap, and available from all PCB suppliers. What’s more, it has really long shelf life, and good resistance against oxidation and against handling.    However, its surface flatness is difficult to control. This could be an issue for components that are sensitive to surface flatness like BGA, fine pitch components, etc. The hole size may not be uniform which could be an issue where press fit connectors are used. And HASL is not suitable for RoHS application.

Electroless Nickel Immersion Gold   ENIG is a chemical plating process where a thin layer of nickel and gold is deposited onto the copper surfaces. The gold preserves the copper below and it remains solderable and conductive with very low contact resistance. ENIG’s surface flatness is excellent, suitable for BGA or other fine pitch components, and also available from all PCB suppliers. Like HASL, it has good shelf life and good resistance against oxidation and handling.    However, it requires a tightly controlled plating process to prevent excessive gold being plated, and not suit some high frequency or high-powered RF application. Besides, its processing cost is much higher because gold is used in plating solution.

To be continued…

Use A Chassis Ground

Similar to grounding yourself and a computer tower case before you start pulling things out, you can ground the external casing of your PCB board. By allowing your board and chassis to share a ground, you can improve the grounding of the entire system. One of the easiest ways to implement a chassis grounding is to include a “chassis screw” that connects the ground plane to the chassis. However, you need to make sure you’re using adequate standoffs so other components aren’t crushed or shorted to the casing when the PCB is screwed in. 

Additionally, grounding with a chassis screw makes ESD protection circuits more effective when you’re using transient voltage suppression at inputs. Remember, you’ll want to separate the chassis ground from the digital and analog ground by using inductive components. That way, a discharge into ground won’t accidentally be shared with all your other components.

If you are designing high-speed circuits, you know that they are always more difficult to optimize for performance. This is especially true if you’re routing across multiple ground planes, like a chassis and a PCB layer. The best case scenario is that you can connect the chassis ground directly to an earth ground. If that’s not an option, you should keep all of the ground planes tightly coupled to each other. That will help to minimize any “ground shifts” around key components.

Lead Free HASL

Although lead free HASL (LFH) has some issues to overcome to modify its tarnished reputation urgently, this not so popular surface finish is consistently gaining popularity amongst customers making manufacturers give it a second look as a main staple up against immersion silver, OSP, and immersion tin. But why? In this article, we’ll say something about LFH.

Actually, LFH needs to be applied at a hotter temperature. On the first pass the surface is left grainy and dull. Once a second pass is added the surface and appearance improves to a shiny, much flatter, and smoother even coat. 

After a lot of changes to chemistries and processes lead free HASL is now a stable surface application to use on PCBs. This longtime reliable surface finish is still used today in military, aerospace, medical, and other applications.

ENIG, OSP and even immersion tin and silver all took the lead in manufacturing while lead free HASL was still a process headache. However, as technology develops and continues to do so, real estate on surface becomes tighter and foot prints decrease, it is clear LFH still can prove itself to be a winner.

How Does SMT Work?

Surface mount technology is the widely-used alternative to through-hole printed circuit board designand manufacturing practices. Today an increasing majority of PCB devices are available as SMDs or packages, making the adoption of SMT board designs and manufacturing practical and cost-effective.

In a simplified view of SMT manufacturing, fabrication generally consists of several highly-automated processes:

Board material contains solder pads without holes, to which solder paste is applied with a screen-printing-like process. Solder placement can be controlled through the use of a precise stencil template for the individual PCB being fabricated, to apply the material only where needed.

Automated component picking and placement machines then position the desired SMDs and other components on the boards precisely. Boards then continue to soldering operations which heat the solder pads to the point where the applied solder paste melts and bonds the components to the board.

Where heat-sensitive components are incorporated on the PCB, these may be installed after the automated soldering, either manually or through processes that would not damage the component. Boards are subsequently “washed” to remove excess flux or solder residues that could cause shorting of components due to their extremely close placement tolerance.

After that is the final inspection of quality including missing components, alignment issues, or soldering issues that could generate potential problems. Inspections of SMT boards can also be automated. Equipment is available that retains a visual image of the correct board construction, and compares the boards produced to the reference image. 

Is PCB Waste Really A Problem?

Compared to the past 100 years, PCB industry really experienced an amazing expansion from using brass wire and pieces of wood to etched copper traces and fiberglass substrates. There are millions of PCBs in existence today, and that number will be expanded day by day.

The funny thing is that we design PCBs to last for years and years, but the devices they power often only last a few. So consumers have to throw them out and buy the new gadget. Obviously, this will cause countless electronic waste.
Is PCB waste really a problem? Not only is PCB rubbish real, but the durability and toxicity of PCBs also make it a problem.

Environmental groups estimate that 25,000,000 tons of electronic waste (e-waste) is produced worldwide every year. About 82% e-waste ends up in landfills. While we take pride in our PCB designs, the devices they power are often made to a lower standard. Our PCB might last 20 years, but the smart fork they put it in only lasts 1 year. When that bad idea is buried in a landfill the PCB inside will still be there for years, leaching toxins into the ground.

Well, what if a board is recycled instead of thrown in a landfill? Most recycling processes are hazardous and have serious health risks. In addition, they are labor intensive. This means that boards have to be shipped to countries with low labor costs for recycling. These logistical tricks still ultimately result in high PCB recycling costs. It is said that biodegradable PCBs can solve this problem to some extent, hope it is really useful.

How to Avoid Solder Bridge?

Solder bridges or shorts have become more challenging to deal with for those who fabricate or manufacture printed circuit boards. A solder bridge or short occurs when a solder is connecting and crossing one lead to another lead improperly. What makes them difficult to deal with is the fact that they are microscopic, which means that they can’t usually be detected by the naked eye if one is present.

So can we avoid solder bridges before detecting them by machine. The good news is that the answer to this question is an absolute yes. As we know, shorts are extremely difficult to identify before it is too late. This begins in the design process. Meeting with your manufacturer and listening to their thoughts and expert advice when it comes to the fabrication process can prove extremely beneficial and definitely avoid some additional costly mistakes in the entire practice. Listening to the manufacturer  is important, if they do find a flaw in the design they will immediately start developing a work around or an alternative solution that will ensure the successful completion of your printed circuit project.

Solder bridges account for about 15% of the problems that manufacturers may face while creating your printed circuit board. The best advice to follow is to be as careful as you can during the design process. Design flaws are normally the main reason for solder bridges. Finding the flaw or better yet not making a mistake in the design process would be the perfect way to avoid them.

Ways to Avoid Embedded PCB ECOs

Engineering change orders (ECOs) not only will drive up design costs but also can cause numerous delays in product development that in turn lead to costly extension of time to market. Fortunately, most ECOs can be avoided by paying careful attention to seven critical areas where problems frequently occur: component selection, memory, moisture sensitivity levels (MSL), design for test (DFT), cooling methodologies, heat sinks, and coefficient of thermal expansion (CTE).

MemoryThe same principles hold true for memory selection. With the constant emergence of new generations of more advanced DRAMs and flash, the PCB designer is challenged to stay ahead of the technology curve and determine how ever-changing memory specs affect newer designs. 

Moisture Sensitivity LevelMoisture sensitivity level (MSL) is easily ignored. If an OEM doesn’t factor in MSL in a design and the critical MSL specifications aren’t properly called out, then there is a possibility that the CM house won’t take the MSL information into account and circuitry will not work properly in the field. This is especially true if MSL levels like 3, 4, or 5 exist. As a result, baking might not be properly performed and moisture might creep in, resulting in ECOs. Where LGAs are involved, the PCB assembly house will have to replace those packages on the PCBs.

Design for TestDesign for test (DFT) is critical for production runs when PCBs undergo test and debug. When placing components on a board, it is important to pay close attention to the placement of DFT probing points and the angle at which the probe comes in to touch vias, pads, and other test points. When DFT has not been allowed for early in the initial design, testing becomes a major issue and ECOs are generated. In some extreme cases, a re-spin is required to address the issue because ECOs may not work.

To be continued...

How Does SMT Work?

Surface mount technology is the widely-used alternative to through-hole printed circuit board design and manufacturing practices. Today an increasing majority of PCB devices are available as SMDs or packages, making the adoption of SMT board designs and manufacturing practical and cost-effective.

In a simplified view of SMT manufacturing, fabrication generally consists of several highly-automated processes:

Board material contains solder pads without holes, to which solder paste is applied with a screen-printing-like process. Solder placement can be controlled through the use of a precise stencil template for the individual PCB being fabricated, to apply the material only where needed.

Automated component picking and placement machines then position the desired SMDs and other components on the boards precisely. Boards then continue to soldering operations which heat the solder pads to the point where the applied solder paste melts and bonds the components to the board.

Where heat-sensitive components are incorporated on the PCB, these may be installed after the automated soldering, either manually or through processes that would not damage the component. Boards are subsequently “washed” to remove excess flux or solder residues that could cause shorting of components due to their extremely close placement tolerance.

After that is the final inspection of quality including missing components, alignment issues, or soldering issues that could generate potential problems. Inspections of SMT boards can also be automated. Equipment is available that retains a visual image of the correct board construction, and compares the boards produced to the reference image. 

PCB Components on Bill of Materials

An old saying goes in manufacturing: "Cost, quality, and delivery: pick two." Is that always true? Actually, manufacturers can create a lower-cost, high-quality product with reduced lead time—even for complex products such as printed circuit boards. In this post, we will discuss the importance of PCB components on the bill of materials. 

To smooth the actual PCB fabrication process, PCB designers must work closely with their manufacturers as well as component suppliers. The page regarding the BOM is between customers and manufacturers should be exactly the same, so each component needs to have comprehensive documentation: manufacturer and manufacturers’ part number, a quantity per assembly, a reference designator, and a part description. The last must include general information like commodity type, package size, and a component footprint.

Designers should select components for availability first, then unit cost, and then package size. Standard component packages from standard manufacturers will tend to have the highest availability—use these whenever possible. 

SMT components tend to be smaller and less expensive, and can be mounted to both sides of a board, increasing flexibility in design. For all the most rugged applications, SMT components should be considered before through-hole components.

How to Save PCB Manufacturing Cost

Everybody wants to buy things with the best price. In this post, we will tell some tips to save your PCB manufacturing cost as much as possible. 

Equipment Capacity: Factories should provide you with the capacity calculations of each piece of equipment and for each step in the manufacturing process. This should focus on the equipment to produce your product only. You should have a written process flow about which equipment they will be used. This will flag you which machines need to pay for. For example: If your products don’t need a clean room, then fabricating in a clean room is a waste of money. 

Equipment Maintenance: Factory should have a clear maintenance plan for all the machines which is posted on the machine. You should select a machine on the line which will produce your product then review the maintenance schedule and sign off by the maintenance engineers. If the factory has a tool shop then ask for the tool maintenance records. For example: A stamping tool should have a record from the tool maker for every time it is shimmed, sharpened or punch is replaced. Another reason to check the tooling is because sometimes you will find the supplier is not making your parts or part of the production is being outsourced.

It is critical to visit the production line prior to mass production.

SMT Technology

SMT technology is largely used during the fabrication process of electronic devices. It is able to generate mass-produced, smaller, lighter boards with fewer fabrication steps and less setup time, reducing cycle times and fabrication complexity. That’s why PCBs use SMT technology are less expensive and more cost-effective for use in electronics or other products. However, things have two sides; EPCB lists some disadvantages about SMT board construction as follows:

1. Construction of prototypes or manual fabrication is more difficult.
2. Board repair of components is more challenging, not easily done by manual means.
3. Use breadboard materials for construction are not available for SMDs.
4. SMD construction is not suitable when there are requirements for high power or large high-voltage parts.
5. Thermal cycling potting compounds can damage SMD solder connections.
6. Capital outlay for SMT equipment is considerable.
7. SMT design requires more advanced skills than traditional through-hole methods.
8. Not all components are available as SMDs. In such cases through-hole design will remain the only alternative.

Reduce PCB Fabrication Cost

The PCB is the centerpiece of a design. To reduce PCB fabrication cost, here are some specific techniques to keep in mind:

A blind via connects an outer layer of the PCB with exactly one inner layer. A buried via connects two inner layers, and contains no contact with outside layers. These techniques are characteristic of high density circuit boards, and add greatly to their expense. 

A minimum of three board fiducials shall be provided located in a triangular pattern as far apart as possible on the PCB. Fiducials located near the corners of the PCB are preferred.

Aim for the smallest board dimension and the fewest number of layers. Minimize the amount of gold and copper. 

Allow the board fabricator to design the multi-up pallet for smaller boards.

Ensure that the fabricator knows the material specifications of the PCB laminate by indicating this in the fabrication drawing. For RoHS assemblies, the laminate must have a Tg greater than or equal to 175 degrees C. 

Not every fabricator will be able to replicate a particular laminate stack-up. Up front, define the minimum trace width, the minimum distance between traces, and the smallest hole diameter.

Placing fiducials on the top copper layer of a board allows pick-and-place vision systems to detect boards more accurately.

To be continued…

SMT Technology

SMT technology is largely used during the fabrication process of electronic devices. It is able to generate mass-produced, smaller, lighter boards with fewer fabrication steps and less setup time, reducing cycle times and fabrication complexity. That’s why PCBs use SMT technology are less expensive and more cost-effective for use in electronics or other products. However, things have two sides; EPCB lists some disadvantages about SMT board construction as follows:

1. Construction of prototypes or manual fabrication is more difficult.
2. Board repair of components is more challenging, not easily done by manual means.
3. Use breadboard materials for construction are not available for SMDs.
4. SMD construction is not suitable when there are requirements for high power or large high-voltage parts.
5. Thermal cycling potting compounds can damage SMD solder connections.
6. Capital outlay for SMT equipment is considerable.
7. SMT design requires more advanced skills than traditional through-hole methods.
8. Not all components are available as SMDs. In such cases through-hole design will remain the only alternative.

Reduce PCB Fabrication Cost

The PCB is the centerpiece of a design. To reduce PCB fabrication cost, here are some specific techniques to keep in mind:

A blind via connects an outer layer of the PCB with exactly one inner layer. A buried via connects two inner layers, and contains no contact with outside layers. These techniques are characteristic of high density circuit boards, and add greatly to their expense. 

A minimum of three board fiducials shall be provided located in a triangular pattern as far apart as possible on the PCB. Fiducials located near the corners of the PCB are preferred.

Aim for the smallest board dimension and the fewest number of layers. Minimize the amount of gold and copper. 

Allow the board fabricator to design the multi-up pallet for smaller boards.

Ensure that the fabricator knows the material specifications of the PCB laminate by indicating this in the fabrication drawing. For RoHS assemblies, the laminate must have a Tg greater than or equal to 175 degrees C. 

Not every fabricator will be able to replicate a particular laminate stack-up. Up front, define the minimum trace width, the minimum distance between traces, and the smallest hole diameter.

Placing fiducials on the top copper layer of a board allows pick-and-place vision systems to detect boards more accurately.

To be continued…

Types of Resistors by Function

There are many different types of resistors with various composition, characteristics, and functions. Some resistors are used as light sensors, while others are used to measure heat. Today, EPCB will go over four different types of resistors classified by the functions they perform. 

Power Wirewound Resistors: They can handle a large amount of power, usually up to 50W, so they are largely used in high-power applications than other resistors which only can handle a power from 0.25W to 2W. 

Precision Resistors: They have a tolerance level as low as 0.005% which means they only vary 0.005% from its nominal value. Every resistor has its own tolerance value, and that value can tell us how close to the nominal value a resistance can vary. For example, a 100Ω resistor that has a tolerance value of 10%, may have a resistance that is somewhere between 10% above 100Ω (110Ω) or 10% below 100Ω (90Ω). Because precision resistors vary very little from their nominal values, so they are largely used in ultraprecise applications.

Fusible Resistors: A fusible resistor is a wire-wound resistor used to burn open easily when the power rating of the resistor is exceeded. In a sense, a fusible resistor serves dual functions. When the power is normal, it serves as a resistor limiting current. While when the power rating is exceeded, it functions as a fuse, burning up, and become an open in the circuit to protect components in the circuit from excess current. 

Cement Resistors: They are of heat and flame resistant which is designed to handle a large amount of power flowing through it without being damaged by heat or flames. Typical power ratings range from 1W to 20W or more, and tolerances from the stated resistance value are around 5 percent.

Types of Resistors by Composition

There are many different types of resistors with various composition, characteristics, and functions. Some resistors are composed of carbon, while others are composed of metal-film. We’ll go over three main types of resistors based on their composition: carbon-composition resistors, carbon-film resistors, and metal-film resistors. 

Carbon-Composition Resistors: Carbon-composition resistors are resistors that are made of finely divided carbon mixed with a powdered insulating material as a binder in the proportions need for the desired R value. More carbon means less resistance, while more binder means more resistance. Carbon-composition resistors often are cylindrical with a brown body. The resistance values of carbon-composition resistors are commonly vary from 1Ω to 20MΩ, and the power rating is generally 0.1W, 0.125W, 0.25W, 0.5W, 1W, or 2W.

Carbon-Film Resistors: A carbon-film resistor is a resistor in which a thin film of carbon is deposited onto an insulated substrate and then cut into a spiral body. More carbon means less resistance, while more insulating material means more resistance. Carbon-film resistors have the following advantages: lower and tighter tolerances, less sensitivity to temperature changes and aging, and less noise generated internally.

Metal-Film Resistors: A metal-film resistor is a resistor in which a thin film of metal is sprayed onto a ceramic substrate and then cut into a spiral body. Unlike the above two resistors, the resistance value of a metal-film resistors are complicated which is determined by the length, thickness, and width of the metal spiral simultaneously. Compared three resistors, metal-film resistors perform the best, while carbon-composition resistors the last. 

Audio Taper Potentiometers

Audio taper potentiometers are specifically designed for audio applications. Audio taper potentiometers are used to control volume in audio devices, including headphones, headsets, computer speakers, or any volume-altering devices.

Audio taper potentiometers are log tapers, meaning any turn in the wiper of the potentiometer changes the resistance logarithmically. And that is an ideal way, because logarithmic change in resistance is more suitable for ours ears to perceive sound. 

Compared to audio taper potentiometers, use a linear potentiometer for volume control to increase or decrease sound may less accurate, because the volume changes may not turn out right as a linear taper's adjustment grows too rapidly as a pot is turned up from zero. This means that the volume levels shoot up too high when you beginning turning it up, so it is very difficult to control volume. However, log tapers are perfect for audio applications. Its characteristics are suitable to the way our ears receive increasing or decreasing sounds. It gradually increases sound as the wiper is turned. That’s why audio taper potentiometers are so widely used in audio applications.

Potentiometer

A potentiometer is a useful device used to represent a wide range of resistance. Just simply adjusting it, we can know a wide range of resistances in a circuit from anywhere near 0Ω to the specified resistance rating of the potentiometer. For instance, a 5KΩ potentiometer can be adjusted to give the resistance range from almost 0Ω to 5KΩ by adjusting the potentiometer knob.

Potentiometers are widely used in circuits, because they can increase or decrease the gain of a signal in a circuit. That means when the resistance of the potentiometer is decreased, the gain of the signal increases; or when the resistance is increased, the gain of the signal decreases. And the function can be used in circuits to control volume levels, such as the speakers, microphones.

Potentiometer Resistance Taper

Potentiometers come with a resistance taper- either linear or log. This explains how a resistance changes in value as the wiper of the potentiometer is turned. 

Linear Tapers: Linear taper potentiometers can change resistance in a linear fashion as you turn the wiper. They are the most common type of potentiometers and are widely used in potentiometer applications.

Log Tapers: Log taper potentiometers can change resistance logarithmically as you turn the wiper. They are mainly used in audio because its characteristics are suitable to the way our ears receive increasing or decreasing sounds. It gradually increases sound as the wiper is turned. Log taper potentiometers are perfect for audio applications, but that doesn’t mean they are not suitable for other applications.