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TECHNET  April 2008

TECHNET April 2008

Subject:

Re: Ionic Contamination Question (& added info).

From:

Hernefjord Ingemar <[log in to unmask]>

Reply-To:

TechNet E-Mail Forum <[log in to unmask]>, Hernefjord Ingemar <[log in to unmask]>

Date:

Mon, 21 Apr 2008 09:35:22 +0200

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (204 lines)

Well written, Terry! General areas of a board is seldom a contamination
problem, but ENTRAPMENTS, yes! And one can not be sure the ionic
contamination test tells you about them.
/Inge 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Terry L. Munson
Sent: den 18 april 2008 22:35
To: [log in to unmask]
Subject: Re: [TN] Ionic Contamination Question (& added info).

Bill
As one of the active task group participants during the 90s when we were
asked to update the equivalence factors table and using low  solids
cleanable and no clean formulations,  we found it difficult to  assess
these new types of low solids residues and if you look at the large
detailed report from the task group (IPC TR 583) we found it difficult
to  correlate between static and dynamic systems.  The use of higher
pass fail  criteria were in place for automotive users (one in
particular used  28 ug/in2 instead of the 14 ug/in2 from
1978 to 1991 with no field  performance problems related to flux
residues with mean levels at 21 ug/in2  while using an 18-24% solids RMA
flux) that did not see problems.  
 
My concern with cleanliness is not the generalized cleanliness of a
total board but the amount of contamination present between pads, in
via's or thru-hole devices.  The pocket of contamination below an 0805
capacitor has  created drained batteries when the entire assembly tests
clean by ROSE and by  bag extraction Ion Chromatography. It is only when
we look at the localized  pocket of contamination do we see the direct
correlation to field and  reliability performance.  Many of the
localized areas we look at with the  C3 tester are clean and show low
levels of contamination, but when we see the  combined processing
effects of selective wave soldering using a pallet to  isolate the area
we find that the residues that can be trapped between the  pallet and
circuit board (low solids no clean VOC free) are also protected from
the heat but are very corrosive due to the water carrier and acidic pH
2.35.  Dendrites are growing in these nearby areas, as well as stray
voltage problems  and intermittent performance issues and No Trouble
Found (NTF) returns.  
 
It is important to understand the cleanliness of an assembly but it is
more important to understand the cleanliness of the processing steps
such as 1st reflow, 2nd reflow, wave soldering bottom and top side, bare
board unsoldered areas, micro via's that have fabrication residues
trapped inside causing performance problems and the hand solder / touch
up residues.  This type of cleanliness understanding comes from being
able to do localized non-destructive residue assessment and ion
chromatography analysis. 
 
 
Cleanliness testing must predict field performance.  Using localized
testing is the only way I am aware of understanding how much
contamination is present in the areas of critical circuitry that tends
to fail earliest. 
 
Terry Munson
Foresite
765-457-8095
_www.Residues.com_ (http://www.Residues.com) 
 
 
 
 
In a message dated 4/18/2008 1:54:54 P.M. Eastern Daylight Time,
[log in to unmask] writes:

As  perhaps the only person still around that attended the meetings    
resulting
in the equivalence factors and IPC Cleaning &  Contamination  Chair  at
that time, perhaps a few points would  facilitate the  discussion:

1. The Navy set up the ionic testing  development program to  solve a
serious 
 
failure problem in S.E.  Asia. 
It worked.

2.  In the timeframe when the test was  developed and put in place by
the   
military, most of the rest  of the electronics industry in the US used
the mil specs  since they were free.

3. As the IPC set up and  adopted Classes  1-3 (basically toys up to
military/high rel), I asked  the  committee if we used the mil test
result for Class 3, could we  use  1.5x that limit for Class 2 and 2-3x
for Class 1? 
The response  was that with  proper cleaning, the mil limit could
readily be  
 
achieved while serving  to monitor daily production. So the industry
continued to  use the  (free) mil spec test  standard.

4. The ionic contamination test was a  valuable  monitoring tool, since
the SIR tests were done on coupons,  not  on actual assemblies, and took
1-2 weeks to complete. Needless  to  say, a high volume electronics
producer could turn out 

a  significant  volume of PWAs during that time, often shipping them
into the field as  soon as assembly was completed.

5. As  noted in my SMT column (offered  yesterday) T. O.  Duyck of
Northern  
Telecom was charged with  implementing water soluble flux for   NT 
electronics
production. During  that time he observed and reported  the  differences
in flux residue  release rates, pointing  out that rosin ca 90% of
rosin flux residues  
release from  the PWA surface during the 10-15 test time for  ionic test

equipment, while water soluble flux residues may take up to 2 hrs.  to

achieve the same
level of release. Thus the release  rate should be checked  to  ensure
the flux used, time test  time and the instrument employed  provide
reliable results and  guidance to the production engineer. 
(See T. O. Duyck and M. Boulos,  "Water Washes  Reliability into
Telephone Circuit Packs", IPC-TR-206,  April, 1978)
Based on this work, I investigated the release rate of   SA flux
residues, 
finding it even faster than rosin fluxes. (See W. G.  Kenyon,
"Synthetic Activated (SA) Flux Technology: Development,
Commercialization,  Benefits and Future Applications", Internepcon
Japan, 24 Jan.  1986)

6. In the late 1980's, the materials and  acceptance of the  no clean or
low residue or acceptable dirt  concept became widely  accepted and
implemented on the  designs  of the time. Outsourcing to  contract
assemblers (both in the US and
overseas) became widely practiced,  so much of the former 'in-house'  
cleaning
expertise disappeared. 

7.  This was seen at IPC as  the number of company sponsored volunteers

dwindled. Could we  take on projects today to develop an updated ionic
test  
for   pr
ocess monitoring? Find enough participants to conduct   statistically
sound  
round 
robin testing?   

Bill   Kenyon
Global Centre Consulting
3336 Birmingham  Drive
Fort Collins,  CO  80526
Tel: 970.207.9586    Cell:   970.980.6373




**************Need a new  ride? Check out the largest site for U.S. used
car 
listings at AOL  Autos.       
(http://autos.aol.com/used?NCID=aolcmp00300000002851)

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**************Need a new ride? Check out the largest site for U.S. used
car 
listings at AOL Autos.      
(http://autos.aol.com/used?NCID=aolcmp00300000002851)

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