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April 2008

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Subject:
From:
"Thayer, Wayne" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Thayer, Wayne
Date:
Wed, 16 Apr 2008 10:00:40 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (158 lines)
I believe the intent of the specification is to make sure that there is
enough flexibility in the attachment structure to make up for planar TCE
issues between the part and the board it is mounted on.  As the pictured
fillet does not interfere with that, it should be a pass.

That is just my opinion, using logic.  Perhaps someone responsible for
the standard could address this.

Wayne Thayer 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, April 16, 2008 9:51 AM
To: [log in to unmask]
Subject: Re: [TN] Inward formed L-shaped ribbon lead - solder

Well, I asked the instructor here, and he said that according to the
-610 it is a defect. But then he added that you'll more than likely have
that if you are coming anywhere close to the maximum fillet height and
that defect is something that you'll probably never be able to see
unless you do a cross section like you did.

Just from my perspective; I've never worried about it and don't think
that I've ever built a board that ever had a problem that was
attributable to excess solder on the inside bend. I'm sure I've built
boards that had solder there. I've waved boards that had bottomside SMT
L-shaped ribbon leaded components and again, I don't see how you would
be able to keep the solder from wicking there.

Jack, do you have your ears up?

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Wednesday, April 16, 2008 7:48 AM
To: [log in to unmask]
Subject: Re: [TN] Inward formed L-shaped ribbon lead - solder

Good Morning Jan!

I have your photos posted. They're at:

http://stevezeva.homestead.com/files/tantal01.jpg

and:

http://stevezeva.homestead.com/files/tantal02.jpg 

In my opinion it's not a defect. I don't know how you would prevent the
solder from wicking there during reflow...but that's just my opinion.

In fact what I'll do is ask an IPC Master Instructor that we have here
certifying some people here for -610 instructors and see what he says.

Kind regards,

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lamote, Jan
Sent: Tuesday, April 15, 2008 11:16 AM
To: [log in to unmask]
Subject: [TN] Inward formed L-shaped ribbon lead - solder

Technet,
During cross section analysis we came across the section of a tantalum
capacitor.
The soldering was flagged as non conform IPC-A 610D. 
In section 8.2.11 Inward Formed L-Shaped Ribbon Leads, table 8-11
indicates for class 1, 2 and 3 states for the maximum fillet height
:"Solder does not contact the component body on the inside of the lead
bend."

If you now have a contact between the bottom corner of the component
body and the solder, is this a defect ? 
(have some pictures if needed, don't know if there still is a "technet
image upload service")

After asking different people I got answers ranging from "reliability
hazard" to "common with these types of components and acceptable"
(including independent lab, EMS, IPC training organisation...)

If something is a defect in all classes, seems to me that there must be
good reason why it is unwanted.
If it is common and acceptable, then I would expect to see it listed as
such in the standard.

Can anyone explain how this rule needs to be interpreted and what the
real dangers are ?

thanks,
Jan.



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