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September 2004

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Subject:
From:
Mike McMonagle <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Mike McMonagle <[log in to unmask]>
Date:
Thu, 16 Sep 2004 06:17:25 -0500
Content-Type:
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Mike and David,

Any ideas of the possible mechanisms that can cause fractures in hand
soldered through-hole parts using Sn5/Pb93.5/Ag1.5 HMP alloy? Pretty
much the opposite of Bryan's Sn96/Ag4, we're lead-rich and tin-poor....

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner
Sent: Thursday, September 16, 2004 2:51 AM
To: [log in to unmask]
Subject: Re: [TN] HMP Solder Joint Cracking


Good thought. The slow cool down associated with larger parts will give
what are effectively shrink holes (like in a solder pot) especially with
Sn96.
[On hand soldering parts with poor solderability operators tend to put
more solder on as well which exacerbates the problem.] The solutions
offer themselves, but you could also consider using a SAC alloy. The
different structure of the solder on solidification should help. If
nothing else the "cracks" will be more rounded. A final thought to
double dot and cross the Ts and Is. In the unlikely event the turrets
are brass they should have a NI or Cu barrier plate to prevent the
solder sucking out Zn. This would certainly lead to a cracked appearance
if not cracks. Regards

Mike Fenner
Indium Corporation of Europe

T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
W: www.indium.com
Pb-free: www.Pb-Free.com




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, September 15, 2004 11:50 PM
To: [log in to unmask]
Subject: Re: [TN] HMP Solder Joint Cracking


Hi Bryan! One possible root cause to explore is that the "cracks" you
have observed are actually shrinkage voids/cavities that intercept the
solder joint surface. There have been several studies (NIST, NCMS) that
have show that the high tin content solder alloys can form small
shrinkage cavities that terminate at the solder joint surface. These
shrinkage cavities could easily be mistaken for cracks. I recommend you
microsection one of the suspect solder joints to see if you have a crack
or a shrinkage cavity. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




                      "Kerr, Bryan"
                      <bryan.kerr@AMSJV        To:       [log in to unmask]
                      .COM>                    cc:
                      Sent by: TechNet         Subject:  Re: [TN] HMP
Solder
Joint Cracking
                      <[log in to unmask]>


                      09/15/2004 10:27
                      AM
                      Please respond to
                      TechNet E-Mail
                      Forum; Please
                      respond to "Kerr,
                      Bryan"






The cracks occur immediately on alloy solidification - I've watched it
happen under a scope. Can't be sure that some don't occur later but that
is a worrying thought which could affect reliability.

Cheers

Bryan

-----Original Message-----
From: Marsico, James [mailto:[log in to unmask]]
Sent: 15 September 2004 16:21
To: 'Kerr, Bryan'
Subject: RE: [TN] HMP Solder Joint Cracking


When are the cracks occurring?  Ate the assemblies thermally stressed
after the terminals are soldered?  Do the cracks occur after a wire is
soldered to the turrets?

Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]> 631-595-5879



        -----Original Message-----
        From:   Kerr, Bryan [SMTP:[log in to unmask]]
        Sent:   Wednesday, September 15, 2004 11:07 AM
        To:     'Marsico, James'; IPC Mailing List (E-mail)
        Subject:        RE: [TN] HMP Solder Joint Cracking


        Thanks Jim

        We are seeing some of the edge solderability issues that you
mention however
        there is definite cracking as shown in microsections done by
ourselves.
        Another batch of pins has better solderability at the edge
however we still
        get cracks occurring.

        Cheers

        Bryan

        -----Original Message-----
        From: Marsico, James [mailto:[log in to unmask]]
        Sent: 15 September 2004 16:04
        To: 'TechNet E-Mail Forum'; 'Kerr, Bryan'
        Subject: RE: [TN] HMP Solder Joint Cracking


                       *** WARNING ***

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             Keep this in mind if you answer this message.

        We've seen this problem in the past.  The main culprit, in our
case, was the
        solderability of the terminal on the corner of the swaged area.
What looks
        like a crack may be an unsolderable line around the periphery of
the swaged
        area.  Try dipping the swaged end of a terminal into a solder
pot and see if
        the corner edge wets.

        Jim Marsico
        Senior Engineer
        Production Engineering
        EDO Electronics Systems Group
        [log in to unmask] <mailto:[log in to unmask]>
        631-595-5879



                -----Original Message-----
                From:   Kerr, Bryan [SMTP:[log in to unmask]]
                Sent:   Wednesday, September 15, 2004 10:35 AM
                To:     [log in to unmask]
                Subject:        [TN] HMP Solder Joint Cracking

                Hi

                We are fitting a swaged turret terminal and soldering
using 96% Tin
        4%
                Silver alloy and have experienced cracks running around
the edge of
        the
                swage solder joint - between the pin and the solder.
Re-soldering
        gets rid
                of it in most but not all cases. I have thought that
perhaps some
        stress
                relaxation is occurring in the swage area (brass base
material)
        during
                soldering resulting in these cracks.
                Can anyone shed any light on this problem ?

                Cheers

                Bryan Kerr
                Principal Quality Engineer
                Process and Materials Laboratory
                AMS Hillend


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