Hiya, Steve,

BGA's, especially CBGA's have given us a real headache, mostly because the
assembly process has to be spot on. We're making VME conduction-cooled
cards with both PBGA's (35x35mm 1.27mm pitch) and CBGA's (21x21mm 1.27mm
pitch), that are used in an avionics box. We had some boards made where the
manufacturing process was OK for the other components but the BGA solder
joints looked a little rough for avionics quality standards. They survived
initial temperature cycling, but failed very quickly with only gentle,
single axis vibration perpendicular to the board surface. The poor joints
were blamed and we're working on improving the process with a different
board stuffer.

From more long-term experience in a previous prison camp, it was LCC's,
particularly 20 pin LCC's that showed signs of solder joints cracking under
qualification testing (15g accelerations and thermal cycling from -40 to
+125 deg). The problem was improved by putting a pad underneath to lift
them off the board surface and using a stepped solder stencil to deposit 10
mils paste on the pads for these devices. The higher solder joints gave
greater flexibility.

My 2 cents worth.

Pete Duncan




                    "Stephen R.
                    Gregory"             To:     [log in to unmask]
                    <SteveZeva@AO        cc:     (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
                    L.COM>               Subject:     [TN] Package reliabilty...
                    Sent by:
                    TechNet
                    <[log in to unmask]
                    ORG>


                    05/31/01
                    12:50 AM
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                    SteveZeva






Hi ya'll!

Can anyone comment from experience on what you know as a general rule of
thumb to be the least reliable family of components (LCCs vs. 0.8 mm pitch
BGAs/CSPs), both from a thermal cycling point of view and from the repeated
application of physical stress?

'preciate it...

-Steve Gregory-

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