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Subject:	layer separation
From:	mp3 <[log in to unmask]>
Reply To:	[log in to unmask]
Date:	Mon, 5 Oct 2009 12:55:30 +0530
Content-Type:	multipart/mixed
Parts/Attachments:	text/plain (2046 bytes) , text/plain (812 bytes)

Dear all,

We have been coming across a failure lately in few of the production lots, where in the outerlayer separates from the barrel after 3 times thermal stress. We have been trying to understand the phenomenon, but has not been very successful. The microsection image is attached for reference. Can anyone give your inputs on this phenomenon. Few details on our current process and some inputs after our trials

1. It happens only in the outer layer and all innerlayers including N-1 layers are intact
2. We do plasma desmear followed by a chemical desmear too ( Rohn n Haas)
3. We use Nelco 175 Tg N4000-6 matrl
4. We use undercut drill bits with no. of hits , a max of 300 / single in stack / with Al clad entry
5. We use glass etch too along with desmear
6. We use laminate construction
7. All innerlayers are 70 microns base copper while the outer layer is 35 micron base copper
8. The boards are normal HAL surface finish
9. We did lot of trials and we did 3 and half cycle (!) of thermal stress after etching and found the coupons acceptable. But after the HAL, the same panels were found defective!

All chemical processes were reviewed and all looks to be within the specified limits. Can anybody help us by giving some inputs, whether we are missing out anything.

Thanks in advance

regards

pradeep

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