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Intermetalic Growth with Gold Finishes

Doug Chambers

#17306

Intermetalic Growth with Gold Finishes | 22 August, 2001

I am researching articles with respect to intermetalics growth associated with gold as a final metalization. We are currently looking at a few options that include a 10uin flash followed by a 30uin selective and a total 30uin finish. The concern is what the threshold is for solderability problems and any related intermetalic problems that will be accelerated by a Burn-In environment.

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Doug Chambers

#17307

Intermetalic Growth with Gold Finishes | 22 August, 2001

Sorry for the abridged post� The remainder of the post was to ask if anyone is aware of any papers or proceedings that discuss problems associated with thick gold finishes and intermetalics.

Thanks,

Doug

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#17316

Intermetalic Growth with Gold Finishes | 22 August, 2001

First an administrative point, you can edit the postings that you make on SMTnet. Look for the yellowish-greenish EDIT button at the top of your posting.

Second there are over 170 postings on intermetallic* on the fine SMTnet Production Forum Archives.

Third, You didn't mention a nickel barrier between the copper pads and the gold plating. It SB GT 150 uin.

Forth, your gold plating is waaaay too thick for soldering. The IPC-4552 ENIG specification draft states: * Ni thickness at 3 - 6 microns or 120 - 240 micrinches. * Au thickness is specified as 0.075 to 0.125 microns or 3 - 5 microinches.

If you get more than 3% gold in an eutecticish solder connection, there will be serious problems with brittle connections caused by the amount of gold. From there, you can figure it out. Simple Excel spread sheet and blamo all the rocket science is cast aside.

Finally another good source of information, probably repeated 9 scatzillion times in the fine SMTnet Archive that you'll be searching, is Wassink "Soldering In Eletronics" Electrochemical Publications. Can't go wrong it's THE BOOK.

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