Bev,
The purpose of lead finish, either it is tinned or gold plated or silver
plated, is not only to make the leads solderable, but also to protect the
bulk material from corrosion. A Kovar leg that is not 100% covered will be
attacked and can corrode to the degree that the whole component falls off.
If the leads are bent after tinning, there is still more risk of problems.
So, of course negative wetting is something that the quality responsible
must consider as a high priority case. If you are interested, and if I can
find, I can send some schrecklich photos to you.
Inge
--------------------------------------------------
From: "Bev Christian" <[log in to unmask]>
Sent: den 25 March 2010 18:58
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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