This practice may be blasphemous, but it really is done frequently. Some
coatings do not play well with some flux residues, other combinations
behave better.
If one coats over flux residue, it is very, very important to test for
comparability, adhesion, SIR and ECM, corrosion, etc. I do this on B-24
coupons on a materials, i.e. coating and flux, basis. but this would be
better done using coupons with the metal finish and solder mask used in
the finished product on a coupon with dummy components like the B-52
coupon.
Karen Tellefsen - Electrical Testing
Alpha / 109 Corporate Blvd./ S. Plainfield, NJ 07080
[log in to unmask]
908-791-3069
From: Mike Fenner <[log in to unmask]>
To: <[log in to unmask]>,
Date: 11/06/2012 11:48 AM
Subject: Re: [TN] Limits on flux residue
Sent by: TechNet <[log in to unmask]>
I think Joyce was responding to the sulphur etc question and not the
original one, which was a little different.
Having said that, coating without cleaning is actually somewhat of a
mainstream activity. For example: if you drive a modern car you are,
perhaps
inadvertently, a user of this blasphemous technology.
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Tuesday, November 06, 2012 4:32 PM
To: [log in to unmask]
Subject: Re: [TN] Limits on flux residue
On top of flux residue? NEVER, ever!!!!
On 06/11/2012 17:11, Joyce Koo wrote:
> Conformal coat.
>
> Joyce Koo
> Materials Researcher - Materials Interconnect Lab
> Research In Motion Limited
> Office: (519) 888-7465 79945
> Mobile: (226) 220-4760
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Woolley, M. D. (M.)
> Sent: Tuesday, November 06, 2012 10:07 AM
> To: [log in to unmask]
> Subject: Re: [TN] Limits on flux residue
>
>>From my company's experience a humid condition and sulfur (H@S, SO4-) in
> the atmosphere can accelerate the process. Sulfurous gasses can be found
> in the far east (China, India, and others) from coal fired power
> generating plants, oil refineries, oil pumps stations and from
> vulcanization of rubber). We have found that in the far east the air
> conditioning of the building is turned off at nights and weekends. We
> have found evidence of condensation on vias from the humid atmosphere
> being taken in by the cooling fans while the metal is still cold enough
> to produce local saturation and condensation. We are working with our
> customers to have the air conditioning on all the time, or at least
> dehumidify the incoming air to the point that water will not condense on
> the PWBs' vias at their "cool" temperature.
> mark
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
> Sent: Tuesday, November 06, 2012 7:56 AM
> To: [log in to unmask]
> Subject: Re: [TN] Limits on flux residue
>
> Folks,
>
> A ticking time bomb for leakage and/or perhaps corrosion! How can
> you determine/predict when the two events will occur? What the worst
> case environment that will active either attribute?
>
> Victor,
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Tuesday, November 06, 2012 8:15 AM
> To: [log in to unmask]
> Subject: Re: [TN] Limits on flux residue
>
> Dave, I could not agree with you more. Excellent posting, and excellent
> philosophy.
>
> Too many times I hear someone say "who cares, its no-clean, perfectly
> safe" only to find the hard way that is not true.
> Not only that, but most no-clean fluxes are very effective when applied
> as a very, very thin sheen or veneer (less than 1 mil thick) over the
> BGA pads. You DON'T need gobs, more flux does not mean better wetting.
> Too much also means a better chance that not all of it will be
> heat-activated.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
> Sent: Tuesday, November 06, 2012 7:27 AM
> To: [log in to unmask]
> Subject: Re: [TN] Limits on flux residue
>
> Hi Wayne - no, the JSTD-001 committee has not addressed that aspect of
> No Clean processing because there are a number of product use
> environment influences and process parameters that come into play on
> what is acceptable and unacceptable. Your description would lead me to
> believe that someone has taken extreme liberty in calling something a
> "no clean"
> process. One of the things that we have found most interesting in the
> implementation of a no clean process for a couple of our products is
> that many folks believe "no clean" is a sloppy process and you can leave
> flux residue anywhere on the assembly in uncontrolled quantities. But
> the reality is that "no clean" solder processing requires very careful
> control of what/how much/where you allow flux residues to exist. In my
> view, a "no clean" process actually is a much tighter controlled process
> than a process that utilizes cleaning to insure that product
> functionality is not impacted.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
> From: "Thayer, Wayne - IS" <[log in to unmask]>
> To: <[log in to unmask]>
> Date: 11/05/2012 05:52 PM
> Subject: [TN] Limits on flux residue
> Sent by: TechNet <[log in to unmask]>
>
>
>
> Is there a spec somewhere which limits the amount of residue allowed for
> no clean processing? I just saw a board where a BGA was about 70%
> "underfilled" by flux residue. No, this was not a flux/underfill
> product!
> A quick look at JSTD-001 Section 8 didn't seem to have specific
> guidance on this condition.
>
> Wayne Thayer
>
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