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March 2012

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Subject:
From:
"David D. Hillman" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 27 Mar 2012 17:14:37 -0500
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Hi Leland - you must have something very goofy going on. I  don't have any 
"common" solder alloys that contain Si in my charts up thru 500C melting 
temperatures. As others have suggested, you may have a case of silicone 
contamination. Do you see any evidence of an organic material "charring" 
on that lead interface when you remove the component? 

Dave



Leland Woodall <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
03/27/2012 03:10 PM
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Subject
Re: [TN] Rework Concern and Question






Dave,

I didn't mean to say the toe.  I guess you'd call it the foot, but it's 
the flat area that makes physical contact with the board pads.

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, March 27, 2012 4:05 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question

Hi Leland - I recommend you find out the lead base metal composition. If 
you shot an SEM-EDS of the lead toe, you could be getting the Si from the 
base metal composition and not part of the solder alloy composition.

Dave Hillman
Rockwell Collins
[log in to unmask]



Leland Woodall <[log in to unmask]> Sent by: TechNet 
<[log in to unmask]>
03/27/2012 02:52 PM
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Subject
Re: [TN] Rework Concern and Question






Vladimir,

We analyzed raw components straight out of the tape and reel packaging.
The site selection was on the bottom side of the leads at the toe.

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev
Sent: Tuesday, March 27, 2012 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question

Sorry Ben, it doesn't.
Leland,

What you are saying sounds strange. What does it mean: "We've analyzed the
lead material beneath the SEM and it returns 98% tin and 2% silicone"? Did
you analyzed leads or solder? Where the analysis was taken from? Did you
analyzed leads with pads ripped off?

Regards,

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: "Gumpert, Ben" <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Tue, 27 Mar 2012 18:58:21
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
        "Gumpert, Ben"
        <[log in to unmask]>
Subject: Re: [TN] Rework Concern and Question

Leland,

I won't claim to be an expert, but this website seems to imply something
along those lines.
http://resource.npl.co.uk/mtdata/phdiagrams/sisn.htm

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, March 27, 2012 2:18 PM
To: [log in to unmask]
Subject: EXTERNAL: [TN] Rework Concern and Question

Folks,

We've ran across a strange incident and I'd like a little advice from the
group.

We recently underwent a component vendor change, and part of the first
group of boards were misbuilt due to incorrect polarity (the part marking
was misinterpreted by the vision operator).

Anyway, an attempt to remove the part by our Repair group resulted in
lifted pads on 10 of the first 12 boards.  We've analyzed the lead
material beneath the SEM and it returns 98% tin and 2% silicone.  The old
style component comes off quite easily (within 3 seconds), and an analysis
of its leads shows to be 100% tin.  It's a 6 pin diode with very little
mass.

What's going on here?  Does a 2% silicone mix raise the melting point of
solder by 200 degrees C?

Please help me understand.

Thanks,

Leland

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