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March 2012

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Wed, 28 Mar 2012 07:18:44 -0500
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Hi Vlad - if the surface was heavily oxidized, then a good metallurgical 
connection may have never been made. The solder joint may be more of a 
"cover up" than a connection. Without being able to look at a picture of 
what Leland is dealing with, we can't provide him more focused root cause 
possibilities. A good picture of the solder joint or the bottom of the 
component lead would be really helpful.

Dave



"vladimir Igoshev" <[log in to unmask]> 
03/27/2012 05:43 PM
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Subject
Re: [TN] Rework Concern and Question






Dave, 

If the surface was heavily oxidized then how the component was originally 
soldered???
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 17:24:01 
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 George - yes, what ever is the lowest temperature melting element in 
the "mix", it will typically sets the stage for what will be the initial 
melting point depending on how the different elements can combine/alloy. 
What Leland has been describing almost sounds like "foot in mud" where he 
is not getting a metallurgical reaction at the component foot interface. 
If it was organic driven, we would expect some type of burning or 
charring. Richard may have hit the right clue - what if the component lead 

is a lead-free, high tin content surface finish and was heavily oxidized? 
That would give a poor melting response. I think the Si SEM reading is 
just a confusing factor that my not be related to the issue.

Dave



"Wenger, George M." <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
03/27/2012 03:25 PM
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"Wenger, George M."     <[log in to unmask]>


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Re: [TN] Rework Concern and Question






Dave Hillman,

With your metallurgical background you might be a better person than I to 
make a comment.  I'm not sure I've even had or seen an occasion where 
something dissolved in the bulk solder and increased the 
melting/solidification temperature.  Yes I've seen the leading edge of 
solder as it flows and wets a surface dissolve metallization and freeze 
because the local meting temperature changed but I've never seen that 
happen to the bulk of a solder joint

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]


-----Original Message-----
From: Leland Woodall [mailto:[log in to unmask]] 
Sent: Tuesday, March 27, 2012 4:14 PM
To: TechNet E-Mail Forum; Wenger, George M.
Subject: RE: [TN] Rework Concern and Question

George,

It's been a long day, and maybe I'm not making myself too clear.

We're not being able to achieve a liquidus state with a 700 degree F 
soldering iron.  We're not trying to melt the lead, just the solder that's 

holding it to the PCB.  We're not accomplishing that with the new 
component, so I'm thinking something has mixed with the solder joint and 
has raised the resultant reflow temperature.

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Tuesday, March 27, 2012 4:10 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question

Leland,

Am I missing something?  I don't think it really matter that the lead base 

material or lead surface finish is.  What matters is the solder used to 
attach the lead to the board.  When you desolder a lead you don't melt the 

lead you melt the solder.

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer Andrew Corporation - Wireless 
Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]

-----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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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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