Richard,
I would call into question the thickness of the gold plating on
those boards. Gold that is too thin will allow oxygen to reach the nickel,
oxidizing it. (If the gold is the proper thickness, the mystery will
deepen.) I would speculate that the baking causing the non-wetting is just
a fluke. More likely, oxidation of the non-soldered side of the board
occurred during reflow. If the gold was indeed too thin, you would have had
problems with solderability on the second pass even if the boards were not
baked but processed immediately after the first reflow.
Thanks
Ryan Grant
Advanced Technology Engineer
MCMS
(208) 898-1145
[log in to unmask]
> -----Original Message-----
> From: Richard Tilbrook [SMTP:[log in to unmask]]
> Sent: Wednesday, June 21, 2000 1:30 AM
> To: [log in to unmask]
> Subject: Re: [TN] Ag on Ni - effect of baking
>
> NEW MESSAGE:
>
> Hi folks,
> Sorry, I wasn't feeling well yesterday and did not explan myself at all -
> the
> reason I asked about baking is that we reflowed one side of a surface
> mount board
> (gold on nickel); we then stored it in a 45'C oven as we were expecting
> the
> remaining parts to arrive for this very urgent job. They unexpectedly took
> a week.
> They even more unexpectedly didn't want to reflow properly when we tried
> reflowing.
> I suggested "passivation" as something for the person who brought me the
> problem to
> think about, though I must confess that being an industrial placement
> student, I am
> not best equiped to make that kind of judgement. As I try to follow many
> of your TN
> discussions, and occasionally add when I feel able, I was sure you'd be
> able to
> give better reasons as to the cause and suggestions for either prevention
> or cure.
>
> Thanks and Regards,
>
> Richard Tilbrook
>
>
>
> PREVIOUS MESSAGE:
>
> Hi technetters,
> I'm hoping to find out a bit more about the effect of baking (at 45 deg.
> C) on
> boards with gold on nickel.
> I would be grateful for any info on the sibject, including times,
> temperatures and
> effects, such as passivation.
>
> Thanks,
>
> Richard TIlbrook
>
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