Brian,
Thanks. Yep it helps some.
Hmmm I wonder if this would explain some solderability results we had a while back. We wanted to test the solderability of metal RF cans using a globule block. They were obviously too big as is because of just being big and also because of the thermal heat sinking over the small globule. So we decided to cut them into thin strips - sort of like wide leads. We cut some with tin snips and some with a low speed cross-sectioning saw followed by cleaning in an ultrasonic bath, more DI water as a rinse and then IPA, all at room temperature. The ones cut with the snips soldered. The ones cut with the saw were very poor, compared to the snips.
I going to go back and have more cut out and examine the edges with our SEM. I am wondering if the part of the edge right next to the kerf have particles from the cooling water tray "embedded" in the edges of the edge, if you can imagine what I am trying to say.
Bev
--------------------------
Sent from my BlackBerry Wireless Handheld (www.BlackBerry.net)
-----Original Message-----
From: Brian Ellis <[log in to unmask]>
To: TechNet E-Mail Forum. <[log in to unmask]>; Bev Christian <[log in to unmask]>
Sent: Sat Oct 25 02:40:03 2003
Subject: Re: [TN] Gross surface roughness and solderability
A clean, solderable, rough surface wets much better than a smooth one
and the resultant solder joint is better, because there are more IMs
formed during the short wetting period. There are also surface tension
factors, best illustrated by a ground glass surface being more wettable
by water than a smooth one. However, as David points out, if oxidised,
the rough surface will place a greater chemical load on the flux.
More important is to know HOW the surface is roughened. If it is a
result of chemical or electrochemical (with reservations) means, well
and good. If produced by abrasion, then there is every chance that
abrasive particles will be physically implanted in the metal. If this
happens, dewetting will certainlt occur, maybe even non-wetting in
severe cases. My reservations re electrochemical deposits are that there
are frequently organic additives co-deposited with the metal that may
inhibit good wetting.
Hope this helps
Brian
Bev Christian wrote:
> TechNetters,
> Can gross (and I mean gross) surface roughness of a component
> termination be enough to almost completely retard solderability compared
> to one with a smooth finish? No, this is NOT a case of the roughness
> being a result of a thin coating being completely oxidized or having the
> intermetallic "come through". That is not to say that the coating isn't
> oxidized on the surface, though.
> regards,
> Bev Christian
> Research in Motion
>
>
>
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