Posts Tagged ‘CTE’

What damage does the assembly process do to a pcb? (part 5)

Sunday, August 28th, 2011

In part 4 of this series of posts I discussed the effect moisture has on the printed circuit board at soldering temperatures. I explained the material properties of FR-4 laminate and how they are hygroscopic. We also covered an acceptable practice known as dry baking used to force moisture from the product just prior to being exposed to soldering temperatures. I received some very good comments and feedback regarding part 4 of this blog series. I thought it appropriate to share this feedback in another post.

With regards to sources of moisture, in part 4 of this series I comment upon a practice where some printed circuit board manufacturers shall dry bake the printed circuit boards prior to shipping them. The important thing to add here is that common packaging materials used by the industry do not act as a 100% vapor barrier. The shrink wrap film used only slows down the process of moisture absorption by the product. Moisture in the environment outside the bag shall migrate through the protective film but at a much slower rate. Things to consider are as follows… (more…)

Why can’t I use FR4 with Lead Free Soldering.

Saturday, January 17th, 2009

You can build a printed circuit board and solder it through a lead free soldering temperatures. It is not advisable! I know some designers that use standard FR4 for lead free soldering applications. The designs are simple single and double sided boards. The companies that they work for have done the due diligence to prove out their design and manufacturing process. On moderate to complex designs they specify lead free soldering compliant laminates in place of FR4. The compliant laminates are much more expensive than standard FR4. They made the upfront investment system by doing the testing and evaluating to save money down the road. They know what they can get away with and have the test data to prove it. However, the results are specific to their designs and their assembly process. When in doubt, play it safe and specify lead free soldering compliant laminate. In order to justify the cost of the more expensive laminate you need to understand what happens to the material at high temperatures.

The main challenge faced by a laminate system is (more…)