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January 2004

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Subject:
From:
David Hoover <[log in to unmask]>
Reply To:
David Hoover <[log in to unmask]>
Date:
Fri, 9 Jan 2004 19:44:40 -0800
Content-Type:
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text/plain (185 lines)
Doug,

Also consider the effects of assembling (lead-free temps) a lower layer
count PCB as opposed
to a higher layer count PCB. The higher layer count has a sees a higher
surface temp and longer
dwell to have the full PWA see the proper soldering temperature. (Because of
all the additional
innerlayers acting as heatsinks) There also are considerable differences in
survivability
depending on material types (dicy vs. non-dicy). Hopefully, much of this
will be in discussion
at the upcoming IPC meetings.

Another thing to note. Since the future PCB's destined for lead-free
assembly will be seeing higher
solder temperatures, all the materials targeted for those PWAs will need
complete UL submittal and
recognizition for the new temperature ratings. I know lot's of efforts have
been put into play on
getting a successful soldered lead-free assembly, but we can't forget about
good ol' UL and their
role in the product listing(s).   : /

David Hoover
----- Original Message -----
From: "Doug Pauls" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, January 09, 2004 2:17 PM
Subject: Re: [TN] Qualification of a lead-free process


> What da heck, its only a few minutes left in the day.
>
> Ioan,
> As usual for me, short question, long response.
>
> First, the best thing you can do is attend the IPC meetings upcoming in
> February.  All the best minds to pick on this topic will be there.
>
> 1.    Your questions of qualify the process, begs the return question of
> qualify the process to what standard or specification?  MIL-STD-2000?
> J-STD-001?  An internal standard?  A customer levied standard?  Such
> standards may tell you what tests to run and in what sample amounts.
> 2.    If you are not qualifying to an external standard, and are doing an
> engineering evaluation, how much data do YOU or your internal decision
> makers need to see to feel confident that the change is reliable?  Are
your
> internal decision makers well grounded in the area of materials and
> processes (that would be a first)?
> 3.    Can you choose the Saber board?  Sure.  But, ask your self if the
> technologies represented on that board are representative of your process.
> Will you be doing thermal cycling or vibration testing?  Only two patterns
> (one BGA and one QFP) are wired for continuity testing.  Other boards have
> more patterns.  Debbie Goodwin at Practical Components can talk you
through
> some other options.  If you do choose the Saber, or any other board, are
> the materials representative of what you plan on using.  If they are using
> a difunctional FR4 solder mask, will it withstand the higher reflow
> temperatures.  Whatever board you get, get the Gerbers and have your board
> house make up the board with your intended material set.
> 4.    Ask yourself if the following materials can take the 20-30C higher
> reflow temperatures of the lead free alternatives (bismuth is for
sissies):
> laminate, solder mask, component adhesives, thermal greases, marking inks.
> Does your flux work at 20-30C higher than current?  If so, and you use
> cleaning, will your cleaning chemicals handle a possibly tougher cleaning
> chore?  If conformal coating, will the surface of your mask change causing
> more problems with adhesion?
> 5.    The number of test vehicles depends on the number of tests you plan
> on running.  How is reliability defined in your company?  Jim Maguire, now
> with Intel, once pointed out that a sample size of 3 boards equated to an
> error rate of 60%.  Consider 10 a minimum for a reasonable error rate.
> 6.    OK, if it were me in your shoes (hopefully size 10 or my feet would
> hurt), I would use the Sabre board or a near equivalent as the test
> vehicle, made by one of my approved board shops, for the material
screening
> tests.  Vibration and thermal cycle would give indications of the
> reliability of the solder joint.  Ion chromatography should be used to
> benchmark the cleanliness of the board.  Dielectric strength or some other
> accelerated electrical test should be used to determine if the dielectric
> properties have been degraded by the higher temperatures.
> 7.    After your materials screening work is done, and you have a
candidate
> material and process, select one or more pieces of your hardware, build
> them and then life test them.  Probably 3 sets:  accelerated humidity with
> bias, thermal cycling to failure, and vibration to failure.
>
> Expensive.  Oh yes. Time consuming.  Start now, we only have 4-5 years.
> But, no one can do this work for you for your product.
>
> My 2 cents worth.
>
> Doug Pauls
> Rockwell Collins
>
>
>
>                       "Tempea, Ioan"
>                       <itempea@POSITRON        To:       [log in to unmask]
>                       .QC.CA>                  cc:
>                       Sent by: TechNet         Subject:  [TN]
Qualification of a lead-free process
>                       <[log in to unmask]>
>
>
>                       01/09/2004 02:45
>                       PM
>                       Please respond to
>                       "TechNet E-Mail
>                       Forum."; Please
>                       respond to
>                       "Tempea, Ioan"
>
>
>
>
>
>
> Hi Netters and Free folks,
>
> I have a good one about lead-fee. It is common knowledge that lead-free
> materials and a process have to be qualified. But what would this mean?
>
> OK, I chose the SMTA Saber board as a test vehicle. I approached a few
> paste
> suppliers and I will probably use the products of 2 or 3 of them to stuff
a
> certain number of boards. I will get support and tweak the reflow and wave
> recipes, let's consider this done. But, what next?
>
> First of all, what quantity of boards would be a good test batch for each
> different paste?
>
> Then, I must confess that I am not a reliability guy, so what tests should
> I
> perform? Cleanliness (is it really necessary?), pull tests, vibration?
What
> accelerated joint reliability tests to do? Simply go through IPC 9701 and
> pick something that matches the application?
>
> Any clue would be largely appreciated.
>
> Thanks,
> Ioan
>
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