Well, I'd say that the presence of a proper intermetallic layer in the region is a good indication of a proper SMT process (re-flow profile), but rather irrelevant to the negative wetting angle issue.
A potential problem with a negative wetting angle is that it can (but only can) have/form a stress concentrator.
in some cases of a "generally" (at a low optical magnification) negative wetting angle a close up view (couple of thousands magnification) shows that there is a positive meniscus right at the surface. That one I wouldn't fail.
Regards,
Vladimir
Vladimir
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: "Fox, Ian" <[log in to unmask]>
Date: Fri, 26 Mar 2010 09:20:08
To: <[log in to unmask]>
Subject: Re: [TN] Need some opinions
Bev, my feeling would be that if the other surfaces of the lead
exhibited proper wetting and the only issue was a bulbous heel fillet,
for the reasons you've outlined, and provided a cross section showed
proper intermetallic formation (I'm assuming Cu leads) in the heel
region then I don't think I would necessarily fail it on qualification.
It would though probably lead to confusion amongst operations personnel
with what is and isn't acceptable from an inspection standpoint and for
that reason I'd have to think about it.
Regards
Ian
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: 26 March 2010 01:58
To: [log in to unmask]
Subject: Re: [TN] Need some opinions
Steve,
Gull wings.
Yes, cheap, cheap cheap!
Bev
----- Original Message -----
From: TechNet <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Sent: Thu Mar 25 21:49:18 2010
Subject: Re: [TN] Need some opinions
Hi Bev,
Don't leave us hanging, what components are you seeing that with? I'd
like to have a "heads-up".
This begs the question, why do you think they are doing that? Are things
getting so tight that they're trying to pinch a penny by reducing
plating coverage? Hmmmm...
Steve
----- Original Message -----
From: "Bev Christian" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, March 25, 2010 9:08 PM
Subject: [TN] Need some opinions
> Technetters,
> It seems that more and more component suppliers are not plating their
> leads
> all the way up to the component body. In fact some are getting
downright
> skimpy and only plating to the bottom bend, never mind the upper one.
If
> you
> put down a lot of solder paste you end up with a bulbous joint, a
negative
> wetting angle and a stress concentration point. If you put down less
paste
> and have a co-planarity issue, then you have the potential for opens.
The
> other option of course is getting the supplier to plate higher up the
> leads.
>
> Question: would you consider the condition of the formation of the
> negative
> wetting angles a failure during process qualification?
>
> Bev
> RIM
>
>
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