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.