Posts Tagged ‘FR4’

Simple Yield Improvement. (Part 2)

Sunday, January 6th, 2013

In the previous post we discussed what happens to the printed circuit board structure when it is heated. We discussed how different materials expand at different rates and the effect the expansion rates have on the warp and twist of a Printed Circuit Board (PCB). We also discussed how moisture absorption can increase the degree of warp and twist and the adverse effect it has on assembly yields and potential field failures. We also discussed how dry baking removes moisture from the PCB and how it minimizes if not eliminates potential problems.

In this post we shall discuss the stabilizing effect that (more…)

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…)

Material Allocation

Wednesday, April 27th, 2011

What does it take to build a circuit board? For starters you can’t build a printed circuit board without materials. What types of materials to be used are defined by the customer supplied documentation and or by the methods/release engineer. If requirements are not specified by the customer the methods/release engineer shall default to IPC standards. The various manufacturing operations used are a series of added and subtractive processes. All of which are determined by the methods/release engineer. It takes many different types of chemicals and materials to fabricate the printed circuit board. The most important material is what we start with and that’s the base copper clad laminate.

Base laminate is typically copper clad FR4. FR4 is a composite material consisting of (more…)

Dry baking printed circuit boards.

Sunday, July 19th, 2009

What most people don’t realise is that printed circuit boards are hygroscopic. They absorb moisture from the atmosphere like a sponge does water. Although the absorption process is much slower it does happen. The amount of moisture absorbed is measured and provided on material data sheets provided by most laminate manufacturers. For example  the moisture absorption limit listed on the Isola FR406 data sheet is 0.20 % measured on a .028 inch thick piece of stock laminate. Lead free assembly compliant laminates are even more hygroscopic. For example, Isola IS410 is 0.45 % measured on the same thickness material per the data sheet. Different grades of material from different manufacturers have different moisture absorption ratings. The percentage of moisture absorption increases when you add inner layer circuity and through holes. A low humidity environment results in a slow absorption rate. A high humidity environment results in a fast absorption rate. Moisture shall be absorbed to the point of equilibrium. Once equilibrium is achieved the absorption stops.

Printed circuit boards that have moisture in them can become (more…)