Posts Tagged ‘Td’

What damage does the assembly process do to a pcb? (part 2)

Friday, August 19th, 2011

In part 1 of this blog post I commented upon the affect the assembly process has upon a printed circuit board. The assembly temperatures applied do in fact burn away the epoxy of the FR-4 composite material. The higher the temperature the faster the rate of burn. I touched upon the relation ship between the glass transition temperature (Tg), decomposition temperature (Td) and the Maximum continuous Operating Temperature (MOT). There is another gauge that can be used to help a designer or contract assembler understand this point and that is the Time to delamination test. These are referred to as either the T260 or T288 tests.

What is the T260/T288 Time to Delamination? This is a test defined by (more…)

What damage does the assembly process do to a pcb? (part 1)

Wednesday, August 17th, 2011

A colleague contacted me the other day with a topic that would make an excellent post on this blog.

“How can we solder boards with a Tg of 180°C or even 200°C at temperatures of 225-245°C without damaging the board?  Even with leaded boards the peak reflow temperatures are way above the board’s Tg.  How is this possible?”

The answer is simple. Every time a printed circuit board is exposed to soldering temperatures it becomes damaged. This is the case not only for Lead-Free soldering applications but also for eutectic soldering consisting of tin-lead.

Tg is one of several parameters to be aware of. In the case of Tg most designers refer to the value as (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…)