DC Members:

I am designing a PCB for HAST (Highly Accelerated Stress 
Testing).  The customers requirements are:

DLT (150C, 408 hours)
HAST (130C, 85% RH, 96 hours)
temp cycling (-65C to 150C for devices)
on a 28 bump CSP package. (.4mm pitch, .16mm lands)

The board material recommended by some fabricators is an Arlon 35N 
Polyimide, due to it's stability over temp.

My questions are...

Is this the best material without going overboard on cost?

Is there a soldermask that is very durable and can withstand this 
environment.  We have had problems in the past with it flaking off.

What is the tightest registration of the solder mask that I could 
expect, in order to create the largest web possible between the CSP 
lands.  We only have .24mm between the .16mm lands.

Has anyone done this in the past and already have the formula for a 
successful project?

Thanks in advance.

David Baldwin CID+



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