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February 2014

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From:
Mike Fenner <[log in to unmask]>
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Date:
Wed, 26 Feb 2014 16:33:05 +0000
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Water sol paste is definitely a minority sport, but is used in Class 3 MIL
and avionics. It can be simpler to clean than many no cleans and makes sense
in that regard if you would be cleaning anyway. I am a little out of touch
now with US, but it used to be that West Coast people did more water
cleaning proportionately than anywhere else. Probably a company cultural
thing dating from the days of large mainframe computer people, probably the
most complex assemblies then being made. Not forgetting that solderability
was a novel concept in early days, so a bit of acid flux in the wave machine
was handy when confronted with wooden boards. (Modern OA pastes are often
little different in activity than no cleans however). Basically "If
IBM/NCR/Burroughs etc do it then it must be OK"
.
NO benefit is without a cost and in the case of water sol fluxes, the costs
of simplified cleaning are typically in reduced paste out times compared to
regular pastes and in possible difficulties associated with cleaning delays.
The biggest down side is your product's short working life if assemblies
miss cleaning or are poorly cleaned. Like from years to weeks.
So far as "recommending a good one" is concerned, you need to be aware that
water sol pastes are much more varied in performance than RO and RE types.
The formulation routes can be quite different according to supplier. This
means you need to do a more robust evaluation of materials and process
compared to no cleans. Some pastes will tolerate delayed cleaning (for
example when you are batching up boards for off line cleaning); others might
foam in inline cleaning. This can be affected by machine type as well as
paste type. You will also need to keep in mind that Sod's Law (AKA Murphy's)
is at a higher potential than usual. So you need to do a more FMEA type
approach when establishing your SOP. Eg what happens if boards are not
cleaned, which when it occurs, definitely will be over a long holiday
weekend.
Don't forget also to evaluate complementary products like cored solder wire
and gel fluxes for repair and off line oddball components etc.

Regards 
 
Mike 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Wednesday, February 26, 2014 3:53 PM
To: [log in to unmask]
Subject: Re: [TN] Class III Solder paste, Sn63, Water Soluble

Bob,
You have to read the whole section to understand the requirement.  You 
can't use a type IN (inorganic) flux to solder assemblies.  Way too 
dangerous unless you REALLY know what you are doing, and even then....

So, you can use water soluble fluxes, which fit in the OR designation in 
most cases, but if it is a halide-bearing (which is the L1 designation) 
flux, it is too active to be used as a low solids / no-clean flux.  If 
your water soluble flux is ORL1 or higher (e.g. ORM0, ORM1, ORH0, ORH1) 
you can still use it, but it has to be cleaned and you as the manufacturer 
have to have objective evidence that you clean sufficiently well to 
prevent electrochemical failures. That's what the "data demonstrating 
compatibility" means.

If anyone is interested, I wrote a white paper for the IPC, which will be 
included as an appendix in IPC-J-STD-001 Rev F (sometime later this year), 
which discusses what "objective evidence" and "compatibility testing" 
means.  The upcoming J-STD-001, Rev F, as it stands now in draft, would 
point you to IPC-9202 as one possible way to show compatibility.

Did I answer your question or neatly rhumba around it?

Doug Pauls



From:   Bob Wettermann <[log in to unmask]>
To:     <[log in to unmask]>
Date:   02/26/2014 09:24 AM
Subject:        [TN] Class III Solder paste, Sn63, Water Soluble
Sent by:        TechNet <[log in to unmask]>



Technetters:

According to the JSTD

"Flux shall not (N1N2,Defect Class 3) conform to flux activity levels L0
and L1 of flux materials rosin (RO), resin (RE) or organic"

That being said who is doing class III work, complying with JSTD Class III
requirements and using a water soluble Sn63 paste? (Our std does not
comply) Can someone recommend a good paste?

Bob Wettermann
BEST Inc


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