Daan... some residual materials left behind from some direct metallization
processes may be the culprit. After drill, holes are treated to accept
electrolytic copper plating and may even get 'flashed' with a thin
electrolytic copper plate. Non-plated holes are typically tented and
protected from additional copper/tin plating when the dry film is applied
for the pattern plate process. (tin for etch protection). During the etch
process, most if not all of the copper plating or DM that may be in the
non-plated holes gets removed. If not all is removed or if the residual DM
is left in the hole, it is now susceptible to nickel and gold plating during
the ENIG process.
This is one possibility. Most depends on the process flow of your
supplier...
Happy Hunting!
Tom

-----Original Message-----
From: d. terstegge [mailto:[log in to unmask]]
Sent: Thursday, February 05, 2004 10:13 AM
To: [log in to unmask]
Subject: [TN] Goldresidues in non-plated holes


Hi Technet,

I looked at an ENIG board today and noticed it had some gold-residues
in the nonplated holes.
I always thought that a non-plated hole should not have any plating at
all, but seeing this condition for the second time (the first time was
on a board from another manufacturer and another designer) I almost
begin to think this is a normal condition.
What do you think, is this normal, is it acceptable (I don't think so),
any idea what causes it ? For those who like to see a photograph of
this, see: http://www.smtinfo.net/forum/index.php?showtopic=40

Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net

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