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July 1999

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Date:
Tue, 27 Jul 1999 07:11:03 -0400
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Ivan,
without knowing what type of No-clean you have used, few commends (may not
be valid in your case):
(1) No-clean has many types: thick coating (form a coating after solder,
like conformal coat), low residue, "No" residue, etc.  When select No-clean,
someone usually forget the test process requirement.  If probe test is
required on the solder pads, thick coating type should not be used.
(2) If conformal coating is required after the PWA, low residue or preferred
NO residue type should be used.  The compatibility of conformal coat/flux
residue/solder mask reqeuired study prior to implementation. Conformal coat
with some known cure inhibitors (related to the catalyst/activator used in
the coating) need special consideration.
(3) If rework is required, cleaning of "no-clean" should be part of study as
well.  Normally, no-clean after clean is more active and will cause low SIR
or absorped into solder mask and cause some problem at end of life test.

Spend some time on proper selection of flux is a good investment.  Based on
my observation, lacking of consideration of overall process and tasting
prior to implementation of No-clean is very common.  (normally, the chap
just did flow solder/reflow and SIR study, and get a "go"/"no go"...A rush
"go" usually is managerial "dead line and cost saving driven"
decision...Ivan, you are not the 1st one to face the consequence of lack of
detail study prior to implementation.  As we always say: "pay me less pay me
now; or pay me more and pay me later"...The chances are, pay next to nothing
and worry about later).

my 2 cents... if design allow the test pads (not on solder pads), mask the
test pads before solder (UV curable mask for example).  If solder pads are
used for probing, you may have to change flux (not something you want to do
if the product is qualified...$$$$$$). In the later case, best way is to
make sure no failure at sub assembly level, (yield 99.9% or up). No probing
is required... system/functional test only (risky and a lot of process
engineering work).  "System test only" works well for low cost large volume
product.  Just get rid of the defective PWA instead FA/rework if it is
failed system test.
                            jk
At 08:31 PM 7/26/99 -0000, you wrote:
>Hi Ivan and All,
>
>As you have discovered there really isn't a 'no clean' flux (at least with
>'special' cases, yours - Probe; mine - Conformal Coating).  Somebody correct
>me if I'm wrong but you have a couple of choices - clean the probes, clean
>the boards, or change the equipment/process (i.e.. change the way you test
>and/or solder $$$).
>
>The question I have for the group: Would soldering in an inert environment
>remove the need for flux all together?  I would swear I have seen that
>mentioned somewhere recently (where o where? - was it PC FAB or maybe
>Precision Cleaning).
>
>Hans
>
>Air Force Material Command - We keep them flying!
>~~~~~~~~
>Hans M. Hinners                                 WR-ALC/LYPME Bldg. 640
>Materials Engineer                                      380 Second Street,
>Suite 104
>Manufacturing Eng. Sec.                         Robins AFB GA 31098-1638
>912-926-1970 (Voice) 468 - 1970 (DSN)   912-926-7974 (Fax)
>[log in to unmask]
>
>
>> Hello Technetters:
>> Being new to the list, I do not know if this issue has been discussed in
>> the
>> past, so here goes. What can be done to minimize/eliminate the residue
>> left by
>> the no clean fluxes on the PCB's? We currently have a big issue with
>> residue not
>> allowing our test pin probes to make contact. We have implemented cleaning
>> the
>> probes on a regular basis, but I want to eliminate the issue altogether.
>> If this
>> has been discussed, please point me in the right direction (archived
>> responses).
>> If not, I would really appreciate your help.
>> Ivan Barrios
>> Process Engineer
>> Conexant Systems
>> El Paso, TX,
>>
>
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