Selecting the Right Board Thickness—A PCB Designer’s Balancing Act

Choosing wisely is critical for PCB quality and performance, but it can be tricky depending on size constraints, functional requirements, and environmental factors. While we sometimes have a general idea about assembly requirements or how the board will be used, there can still be a lot of unanswered questions as we begin the manufacturing process. After all, there’s a big difference between a PCB going into a drone and a PCB that will be part of a submersible drone and needs to be the size of a tennis ball, withstand intense heat or cold, and function forty fathoms below the surface.

When we receive a design, there’s a lot we can evaluate before production to ensure its manufacturability and functionality. However, we are limited in our ability to judge whether a board is too thick or too thin as designed. In general, you might think thicker is better because the board will be less brittle and won’t break as easily. But thicker is also heavier, hotter, and not appropriate for many applications or assemblies.

As you design your PCB, you should ask yourself:

  • How thick does it need to be to work?
  • How thin must it be to fit?
  • What will it have to do?

To avoid producing boards that don’t fit into the assembly or fail to perform reliably, choose your thickness carefully. Here are some tips, guidelines, and checklists for ensuring proper fit and function.

Test Your Design Assumptions

Keep in mind, PCB design is often as much an art form as it is a science. It’s not as straightforward as plugging a bunch of numbers into an equation and receiving an answer.

To read this entire column, which appeared in the January 2019 issue of Design007 Magazine, click here.

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2019

Selecting the Right Board Thickness—A PCB Designer’s Balancing Act

02-21-2019

Choosing wisely is critical for PCB quality and performance, but it can be tricky depending on size constraints, functional requirements, and environmental factors. While we sometimes have a general idea about assembly requirements or how the board will be used, there can still be a lot of unanswered questions as we begin the manufacturing process. After all, there’s a big difference between a PCB going into a drone and a PCB that will be part of a submersible drone and needs to be the size of a tennis ball, withstand intense heat or cold, and function forty fathoms below the surface.

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Connect the Dots: Key Guidelines for Clean Schematic Designs

01-08-2019

The smoke has not even cleared, but they already know what the problem is. It was supposed to be a celebratory moment for the team, plugging in the first board from the initial shipment. Instead, the room is as silent as a morgue. The engineer knows that they put the capacitor in place. However, on closer examination, it is not close enough to the IC pad to make a difference. Everyone turns to the PCB designer. “But I put it right where the schematic said to!” they say. The fix is easily implemented. It takes 15 minutes to produce a new design. Unfortunately, the break room already has an ample supply of coasters, and that’s all this batch of boards can now be used for.

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2018

Connect the Dots: Six Tips to Ensure Parts Fit on Your Board

12-12-2018

One of the most frustrating mismatches with alternative through-hole parts occurs when the land pattern matches, but the pin size is off. If hole sizes are too tight, pins may not fit through the holes, or if they do go into the holes, they may not solder well. Solder will need to flow through the gap between the pin and the hole barrel. If there is not enough space to allow enough solder mass to flow through the hole, the circuit board will absorb heat from the molten solder and cause the solder to solidify partway up the hole. This is called a cold solder joint and can result in a premature failure of your circuit.

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Connect the Dots: New Landing Design to Reduce Thermal Pad Failure

11-16-2018

You’ve finally finished your design. All the traces are correct and the IC landings are to the manufacturer’s specifications. A short run of test boards performs perfectly. For best results, you select a reputable domestic board house for production and a quality assembly shop to do the soldering. When the finished boards arrive, everything looks great. You’re in high spirits and congratulate yourself on a job well done. Then the reports start coming in.

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