Hi Mark

Welcome in the club. We have to perform failure analysis on glob tops frequently and in the recent years it became increasingly difficult to remove the glob- tops without destroying the structure of the PCB because the materials used to cover the chips are not pure epoxy anymore but copolymers that solve only partially in hot Nitric acid. We are not able to remove the glob- top safely without destroying the structures on the PCB to a large extend. Presently we work with a first preparation of the glob- top with a laser ablation system that destroys the polymer matrix to a certain extend. After that we etch with water free nitric acid with 30% sulfuric acid at 5°C (takes forever).In the end we burn the molding mass between the bonds out with the laser ablation tool.
Yes you're right it's a mad effort. And it's not sure that we are successful. Fortunately we don't have a lot of customers requesting this preparation. If somebody has a faster way I'll be very pleased.

Have a great day

Günter Grossmann
Scientist
Empa
Swiss Federal Laboratories for Materials Science and Technology
Überlandstrasse 129
8600 Dübendorf
Switzerland
Tel +41 58 765  4279
Fax +41 58 765 4054
[log in to unmask]
www.empa.ch


>-----Ursprüngliche Nachricht-----
>Von: TechNet [mailto:[log in to unmask]] Im Auftrag von Woolley, Mark D.
>(Mark)
>Gesendet: Donnerstag, 11. Oktober 2012 05:59
>An: [log in to unmask]
>Betreff: [TN] Glob Top removal
>
>Does anyone know of a way to remove the epoxy that is used to cover CoB
>ICs, while maintaining the integrity of the PWB-CoB Assembly afterwards?
>I have tried hot Nitric Acid, which does remove the epoxy nicely, but
>also removed the copper on the PWB and swelled during the decap process
>and ruptured the bondwires.  I believe Red Fuming Nitric would also
>swell the epoxy lifting the bondwires.  Most aggressive solvents don't
>remove epoxies well. So I am pout of ideas at present.
>
>Thanks,
>mark
>
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