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March 2012

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Subject:
From:
Robert Kondner <[log in to unmask]>
Reply To:
Date:
Wed, 28 Mar 2012 12:41:44 -0400
Content-Type:
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text/plain (513 lines)
So are we back to the point of:

  "Someone pulled off the part before the solder melted?"

  Much simpler concept than Si or SEM results?

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, March 28, 2012 12:03 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question - SEM EDX Results Posted

Hi Leland,

SEM/EDX has its purpose but whenever we have problems with component
soldering we always do XRF measurements to not only see what the surface
finish is but to also measure the thickness of the surface finish.  What
we've found is that SEM/EDX is great for surface analysis but if you want to
use it for bulk analysis you need to cross section samples and do
measurements at several locations.  I have two suggestions:  1st). I would
do XRF measurements on an old "good" part and compare the results to XRF
measurement on a new "bad" part and 2nd). I would take a board with a
soldered new "bad" part and put it on a hot plate and monitor the
temperature as the board heats and record the temperature at which the
solder melts.

If you don't have access to XRF I would be happy to make XRF measurements
for you.  Just put one old "good" and one new "bad" part in an envelope and
send it to the address in my email signature block below.  The measurements
would only take a couple of minutes.

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: Wednesday, March 28, 2012 11:49 AM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question - SEM EDX Results Posted

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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TechNet E-Mail Forum <[log in to unmask]>; Please respond to Leland Woodall
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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
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Leland Woodall
<[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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