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.

Advantages of Metal Core PCB

Metal core PCBs have been used frequently in electronic products, especially for LED products. In this article, EPCB would like to outline its advantages. 

Thermal Conductivity: For many double-sided PCBs or multilayer PCBs with high density and power, heat dissipation is really a big challenge, because high temperature can make electronic components fail to work. The normal PCB raw material we used frequently now, such as FR-4, has poor thermal conductivity and inter-layer insulation. So we need to use metal core PCB instead, which has an excellent thermal conductivity. 

Thermal Expansibility: There is a physical principle says objects will expand with heat and contract with cold. The CTE or coefficient of thermal expansion is different with different objects. Metal core PCB can effectively deal with the heat and the problems of thermal expansion and contraction, improve the durability and reliability of equipment.

Scale Stable: Compare with FR-4 PCB, the scale of metal core PCB is much more stable. For example, aluminum PCB is heated from 30℃ to 140~150℃, but its scale only changes from 2.5%~3%. So the metal PCB is more suitable to work in the condition of high temperature.

PCB Panelization

Some PCB board is really small with irregular outlines, bringing much trouble to PCB manufacturer process as single pcs. To improve fabrication efficiency, PCB manufacturers usually require panelized PCBs, which not only can shorten PCB manufacturing lead time, but is easy to control quality and count PCB quantity before shipment. In this article, EPCB will outline four types of PCB panelization, and hope it really useful for you.

The most common way is panelization with break-away but without spacing between each single pcs. Most customers do not have any special requirements on PCB outline, so V-CUT is often used to depanelize the PCB into single pcs. 

Compared to type 1, this panel board type has both break-away and spacing between each single pcs. If customers have special requirements on PCB outline and board edge, we will use the profile of routing, thus, it requires spacing between each single board, generally the spacing is within 1.5~2mm. 

As to a panelization without break-away, it is convenient for shipment, but not helpful for follow-up process, but this kind of panelization will save cost for board edge, so the wholr cost can be reduced to some extent. 

Finally is a panelization with stamp holes, PCB manufacturers could use stamp hole connection to control and reduce burs, so the stamp holes can be used to replace V-CUT.

PCB Assembly Process

In this article, EPCB outlines the importance of knowing the PCB assembly process for a  designer or engineer. Five different aspects are considered as follows: 

Inspection: Automatic optical inspection is used by most assembly companies. However, not every company really inspects samples or finished PCBs one by one, some of them just do sample inspection. A short or dry joint is really hard to check by visual, let alone many component packages have connections underneath the component body. So your assembler should check this with some kind of x-ray or specialist visual equipment.

Handling: The way your assembler handles electro static discharge and moisture sensitive components really matters. Though controlling static is often regarded as unnecessary, it is a real risk to components. The same applies to moisture sensitivity, you should be careful about which components are rated as moisture sensitive when designing.

Cleaning: The way a PCB is cleaned can affect components to some extent, so you should pay attention to what kind of cleaning process your assembler uses as standard. With the cleaning process there should be a drying process as well, making sure it’s sufficient to completely dry out the board this is especially needed if using Rogers materials.

Reflow: Generally, it is doesn’t matter what reflow process your assembler uses as standard, however some components can be damaged by vapor phase reflow processes. So have a good command of assembly process knowledge is a must, besides, be familiar with component datasheets is sometimes necessary. 

How to Choose a Microcontroller

How to choose a suitable microcontroller is really hard, at least if you don’t know what you are doing. But we hope you can feel much easier after reading this article.

There are numerous different microcontrollers. But what is really important for your project? Let’s look at some differences between microcontrollers.

You can find 8-bit, 16-bit and 32-bit microcontrollers. These numbers refer to the size of the databus. In practical terms, a larger databus can do more heavy calculations. The 8-bit microcontroller is the most commonly used by hobbyists. In general, the 8-bit microcontroller has fewer pins, so that it’s easier to solder. And it is usually easier to program too.

Different microcontrollers have different amount of memory, number of input/output pins and peripherals. Peripherals are extra functions added to the microcontroller. The two most common microcontroller-brands for hobbyists are probably AVR from Atmel and PIC from Microchip.

Soldering Irons

Soldering irons, a simple iron and a temperature-controlled one, need different wattages while working.

A 30-watt simple soldering iron is okay for modest electronics. Soldering ordinary through hole electronic components and thin wire, even the thin metal legs on direct current power plugs and sockets, should be fine.

While a temperature-controlled soldering iron needs much higher power than a simple iron, for example 80W or more. This allows it to maintain a relatively constant soldering temperature even it is being used at the same time, and heat parts with larger thermal conduction or capacity. It won't slow down an operator, and is a bit more flexible on what it can be used for than a simple iron. That is very important on a production line, or where a lot of soldering joints need to be made relatively rapidly. However, a simple iron is likely to drop too far below adequate soldering temperature, and slow the operator down which will cause boss much loss. 

PCB Design

With the rapid development of the latest technologies, it no doubt that in every few months, you can see a new “product for future” launched and it can really revolutionize how we live our lives. With advances in technology for consumer products, especially in the transportation and communications fields, we are now able to do more than we ever thought possible even a few years ago. As more and more products use printed circuit boards to get the job done, expands its capabilities and continues to grow in order to manufacture the top PCBs for your products and projects. Rather than being limited by the hardware available, you will be limited by just your imagination in the design process. Don’t worry about that, designers in EPCB can give you the most suitable suggestion for your design.