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March 2010

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Fri, 26 Mar 2010 07:35:36 -0700
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A potential problem with a negative wetting angle is that it can (but only 
can) have/form a stress concentrator.......

I'm too.   Can't prove it, but much points in that direction. I'm trying to 
find old reports on that.  Too old maybe. The 5S gang whirl like a tornado, 
and when they  have finished their patrol job, a lot is missing. I had to 
take job material to my home, in order not to let it go to  the waste bin.

Inge
>


--------------------------------------------------
From: "vladimir Igoshev" <[log in to unmask]>
Sent: den 26 March 2010 06:48
To: <[log in to unmask]>
Subject: Re: [TN] Need some opinions

> 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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