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March 2012

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Subject:
From:
Leland Woodall <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Leland Woodall <[log in to unmask]>
Date:
Wed, 28 Mar 2012 19:14:34 +0000
Content-Type:
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Richard,

There is only a single component per board.  We've tried preheating the board and adding flux but it made no difference.  Yesterday I thought they were using tweezer attachments for removal, but found out today we use two soldering irons with tips that extend slightly beyond the span of the 3 leads.

All of our rework operators are certified to IPC 7711/7721, and their experience ranges from 3 to 10 years.  They're excellent at what they do.  They've pulled more pads on these 10 assemblies than most of them pull in a year's worth of work.

There's something here I'm not seeing.  I just haven't figured it out yet.

Leland

-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Wednesday, March 28, 2012 2:41 PM
To: TechNet E-Mail Forum; Leland Woodall
Subject: RE: [TN] Rework Concern and Question - SEM EDX Results Posted

In looking at the pictures you posted, I am assuming a single component location exists on each CCA, not multiples of the same part. In the picture, each of the pads is connected to its own trace. There is no belly pad under the part. There is no conformal coating present. Having said that, this looks like a very straightforward component/solder connection. But in your emails, you mention not being able to get the solder to go into reflow using a 700 deg. F. iron. So my next question is, are they attempting to remove these parts by unsoldering each lead using an iron? That method would definitely result in lifted pads. Or are they using some type of hot air rework? Exactly what method of removal is being performed that results in the lifted pads?
Looking at this CCA picture, I would select a controlled hot gas rework method such as an Airvac DRS24/25 or similar machine with sufficient pre-heater below. Then a process can be set up to repeat exactly the same way every time.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Wednesday, March 28, 2012 1:14 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question - SEM EDX Results Posted

Steve,

I'll have to examine the boards to determine.  I'm not really certain right now.

Leland

-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Wednesday, March 28, 2012 2:05 PM
To: 'TechNet E-Mail Forum'; Leland Woodall
Subject: RE: [TN] Rework Concern and Question - SEM EDX Results Posted

Hi Leland,

Has it been the same pad that's been lifted? Or different ones?

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leland Woodall
Sent: Wednesday, March 28, 2012 1:59 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question - SEM EDX Results Posted

Four different rework operators, each with over ten years of experience, pulled pads in an attempt to remove this particular component.

These are the same four operators who daily perform their function so well it is difficult to recognize their rework actually occurred.  Not saying it couldn't happen, but I find it very odd.

Leland

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, March 28, 2012 1:42 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question - SEM EDX Results Posted

George,

 Sure, measuring the melting point of the folder is fine. But look at what we are suggesting here:

  1. Either the solder used when the component was mounted has magically increased in melting temp.

Or

 2. Someone pulled the part off the board before the solder melted.     <---
My Choice

I have seen and done enough rework to have seen and pulled a few pads.
Rework is not easy. But pointing the finger of blame  to the board house or component? And using some high-tech erroneous SEM results as proof? Come on.


 It sounds like some rework shop trying to squirm out of screwing up a board.

Bob

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Wednesday, March 28, 2012 1:14 PM
To: [log in to unmask]
Subject: Re: [TN] Rework Concern and Question - SEM EDX Results Posted

Bob,

That would be my first guess but rather than guessing I think it would be prudent to measure the melting temperature.  That could be done crudely on a hot plate with thermocouples or you could take samples of the solder from the good and part parts and do DSC analysis which I don't think is necessary.

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: Robert Kondner [mailto:[log in to unmask]]
Sent: Wednesday, March 28, 2012 12:42 PM
To: 'TechNet E-Mail Forum'; Wenger, George M.
Subject: RE: [TN] Rework Concern and Question - SEM EDX Results Posted

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 <[log in to unmask]>


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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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