warpage

[Rod Ladwig]

Hi Tom

Are there any special recommendation to help prevent warpage in PCBS, like using equal power and ground planes in a 4 layer PCB. What are the rules of thumb concerning this?

Thanks

Rod Ladwig
Unique Designs

[Tom]

Rod,

There are a couple of things to consider. The first being balanced board construction. In the printed circuit industry, the term "balanced construction" refers to a printed circuit board that is designed in such a way that all variables relating to copper distribution, dielectric distribution and component distribution are in a word, balanced.

A rule of thumb for a clean layer stack-up is that the top 1/2 has the identical structure as the bottom half.

Your boards might come from fabrication flat, and get warpped in the assembly process because of grossly imbalanced component placement especially when using wave solder. Good assembly shops are aware of this issue and will adjust their processes as needed to prevent warpage.

Most manufacturers can spot potential board warpage before they start construction. They will alert you of the problem and offer recommendations on how to fix it. But it's too late sometimes if you don't address these issues before you start layout.

It is critical that you have your board stack-up approved by your manufacturer prior to starting layout and the part placement should be approved by the assembly shop prior to any trace routing. This will save you and your company both time and money.