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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:
Wed, 28 Mar 2012 10:49:10 -0500
Content-Type:
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Hi Leland - do you have any photos of the "bad" parts after removal from 
the pwa? Looking at the SEM EDX, I agree with Stewart, that Si peak could 
be a misidentification issue.

Dave



Leland Woodall <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
03/28/2012 10:26 AM
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Subject
Re: [TN] Rework Concern and Question - SEM EDX Results Posted






I've also added the SEM photos and EDX results to the folder at 
http://ipc-technet.groupsite.com/file_cabinet.

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Wednesday, March 28, 2012 11:18 AM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question

Everyone,

Thanks for all your responses.  To answer a few of the items brought up 
between yesterday afternoon and this morning:

The solder did indeed reflow and formed what visually appear to be good 
joints.  There is no evidence of dewetting or nonwets.  I see no 
difference between the joints on the old versus the new components.

The EDX analysis was performed on two leads of the old component and two 
leads of the new component.  Both of the samples were taken directly out 
of the tape and reel packaging with tweezers, placed near each other on 
kapton tape upside down, and analyzed within minutes of each other.  The 
old component returned two readings of 100% tin, the new component 
returned two readings of 98% tin and 2% silicon.

When examined beneath a microscope at high magnification, the original 
part leads are somewhat dull and grainy in appearance on the bottom.  The 
leads on the new component are very shiny and smooth.

I've taken a few photos and posted them to 
http://ipc-technet.groupsite.com/gallery/22905.

I'll look through the SEM results from yesterday and see if there's 
anything worth posting as well.

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of vladimir Igoshev
Sent: Wednesday, March 28, 2012 9:18 AM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question

I'm getting more and more anxious to see how much  that "guessing game" 
might contribute to finding the root cause. There are simply not enough 
data to solve the puzzle.

Leland,

If you don't have capabilities to do proper analysis, you can send samples 
to us.

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: "Amol Kane (Asteelflash,US)" <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Wed, 28 Mar 2012 05:36:43
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
        "Amol Kane (Asteelflash,US)"
        <[log in to unmask]>
Subject: Re: [TN] Rework Concern and Question

Leland,
Have you tried preheating the assembly while doing the rework? If it?s a 
RoHS compliant laminate, you can preheat it to 120-130C and try the rework 
then.

Amol Kane
Process Engineer
AsteelFlash US East Corp
Tel:   (607) 687.7669 x349 (O)
www.asteelflash.com


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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, March 27, 2012 5:03 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question

Bob,

At this point, we don't know what has happened nor how high we'll have to 
go to achieve release from the board.  Thus far we've stayed within our 
set standards of 700 degrees F.  We'll experiment tomorrow and should know 
something then.

Gee, I'll never make a reference to 200C again.  Learned my lesson on that 
one.

Leland

-----Original Message-----
From: Robert Kondner [mailto:[log in to unmask]]
Sent: Tuesday, March 27, 2012 4:24 PM
To: 'TechNet E-Mail Forum'; Leland Woodall
Subject: RE: [TN] Rework Concern and Question

Leland,

 So you are suggesting Si defused into the solder and raised its melting 
point by 200C ?

 Did I get that right?

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Tuesday, March 27, 2012 4:14 PM
To: [log in to unmask]
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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<[log in to unmask]>


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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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