Richard,
I was talking about front area of the toe, so there is no disagreement :-)
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: "Stadem, Richard D." <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Tue, 27 Mar 2012 21:11:43
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
"Stadem, Richard D."
<[log in to unmask]>
Subject: Re: [TN] Rework Concern and Question
Not sure I agree with you Vladimir. Most leadframes are stamped out of a larger sheet of copper that has been plated on both sides. The sides of the lead will be bare copper, which typically oxidizes somewhat, but the top and bottoms of the flat leads are plated. The IPC 610 solder joint standards are based somewhat around that principle, thus the emphasis on the heel joint and requirements for at least some wetting around the periphery and top of the foot. Everybody knows the sides may not solder so well, but the plated top and bottom of the leads certainly should.
With that in mind, if someone performed SEM of the top of the toe, they should see some evidence of whatever plating was used. The front or sides of the toe, I agree they may not, but even during the stamping some of the plating will be mechanically sheared, and should show up in the analysis......but NOT if the exposed copper has oxidized.
________________________________________
From: TechNet [[log in to unmask]] On Behalf Of vladimir Igoshev [[log in to unmask]]
Sent: Tuesday, March 27, 2012 5:30 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question
Hi Dave,
With all due respect I completely disagree. What you are saying is applicable in case the plating finish if thin (below 1 micron). But if someone analysts the toe of a lead, all the person should see is only the elements of the lead material, as there is no plating on the toe surface due to the way it's normally made.
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: [log in to unmask]
Date: Tue, 27 Mar 2012 17:11:05
To: <[log in to unmask]>
Cc: TechNet E-Mail Forum<[log in to unmask]>
Subject: Re: [TN] Rework Concern and Question
Hi Vlad - it depends on the selected analysis location and the kV
selection they used during the analysis.
Dave
"vladimir Igoshev" <[log in to unmask]>
03/27/2012 03:25 PM
Please respond to
[log in to unmask]
To
"TechNet E-Mail Forum" <[log in to unmask]>, [log in to unmask]
cc
Subject
Re: [TN] Rework Concern and Question
Dave, if they did that then they wouldn't have seen Sn as leads are
usually chopped off.
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: "David D. Hillman" <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Tue, 27 Mar 2012 15:05:00
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
<[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
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Leland Woodall <[log in to unmask]>
To
<[log in to unmask]>
cc
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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