Hi

Further to the original message I can give some additional information but we
buy the PEC in from a supplier and there are some gaps in what we know to
date.

The board is an eight layer multilayer made from FR4
It has various pth for component leads and via's in it. The via's are 0.3 mm
dia, the pth's are much bigger.
The finish is 20 microns min. of electrolytic copper, approx. 5 microns of
electroless nickel with a gold flash ( approx. 0.5 microns )

The copper solution has regular analysis of its organic contamination using
Cathodic Voltage Stripping (CVS) technique by the solution supplier. I don't
know to what level it is controlled.
The electroless nickel is a Lea Ronal solution ( not sure which ) and is said
to be a high phosphorous content ( approx 12 % )

As far as I know the gold immersion follows immediately after the nickel with
no intervening heat treatment.

The thermal shock which causes the cracks is the standard BS method of ;
Dry @ 125°C for 1 hour min.
10 second float on solder at 260°C

The via's have solder resist in them therefore no solder gets into them. The
cracks propagate through both the nickel and copper. None stop just in the
nickel, all go at least part way into the copper and usually all the way
through and occasionally into the surrounding resin.

One other variable in this is that some batches of the PECs contain some inner
layers with single ply glass fibre. These all have barrel cracking when
shocked. Other batches are all 2 ply construction and in the main are OK but
have occasionally cracked in the same manner as the others.

Any thoughts on this will be of interest.


Chris

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information.
For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311
################################################################