Ohhhhh, I dunno that I would go that far. There are a great many people
manufacturing with low solids flux, doing it well, and not being perfect.
It all goes back to understanding your materials and processes, and
statistically controlling the processes for the proper parameters. I have
seen just as many manufacturers use OA fluxes with water cleaning and
produce scrap with amazing statistical accuracy.
I do agree that if you are not "adequate clean" (and we can argue over
what that means) prior to conformal coating, then you have a latent
failure. Whether it becomes a real failure depends on a great many
factors. As for the cracking over time, that depends on the elasticity of
the conformal coating. Silicones are very elastic, epoxies are not.
Doug Pauls
Rockwell Collins
Paul Edwards <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
11/10/2008 12:06 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Paul Edwards <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] FW: [LF] Accelerated reliability model for SAC405/305 solder
joint creep-fatigue
John,
No-clean fluxes because of there nature will always have SIR problems...
You are never removing the oxides and ionics from the solder joints and
unless you are perfect in process they don't "cure"...
Best to use a cleanable paste, clean the PCA then conformably coat...
Non-hydrophobic conformal coatings add to the SIR problem because they
absorb moisture...Also you want a coating that has a surface skin and
expansion coefficient of the PCA, otherwise overtime you get cracking...
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Goulet
Sent: Sunday, November 09, 2008 7:32 AM
To: [log in to unmask]
Subject: Re: [TN] FW: [LF] Accelerated reliability model for SAC405/305
solder joint creep-fatigue
Is there any information on products with No-Clean flux being effected by
moisture over a period longer than that tested in SIR tests with the SIR
comb test coupons? Some customers make products for vehicles and toys that
are subject to more humid conditions. The No-Clean fluxes used always pass
SIR which have high resistance values even after 196 hours. However if
the humidity levels rise and fall but never to the point of drying out the
moisture. I thinking that the humid spring and summer months could be a
problem if not sprayed with a conformal coat. The other situation I'm
testing is when a moisture sensitive part is used. Tests on three of the
boards showed that the moisture sensitive part was dragging the surface
insulation down. When I localized the heating to this part with a small
Leister heat gun, the resistance across the battery terminals with the
battery removed went back to infinity. Usually the moisture sensitivity is
a factor relative to the SMT reflow proc!
ess and
not an issue in operation. Any info on this? PS this batch was the first
ones using Pb-Free solder paste and that means I'll have to check if the
BOM changed to a different RoHs version of this special moisture sensitive
part.
-------------- Original message --------------
From: John Burke <[log in to unmask]>
> FYI Werner has developed an Accelerated reliability model for SAC405/305
> solder joint creep-fatigue. Details below
>
>
> John Burke
>
> (408) 515 4992
>
>
> -----Original Message-----
> From: Leadfree [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
/*
> Sent: Friday, November 07, 2008 2:15 PM
> To: [log in to unmask]
> Subject: [LF] Accelerated reliability model for SAC405/305 solder joint
> creep-fatigue
>
> Hi all,
> Just to let everybody know, I have developed a creep-fatigue model for
> SAC405/305 solder joints. It will be published in a presentation at the
> IPC/JEDEC
> Conference on Transitioning to Lead-Free: Strategies for Implementation
on
> December 8 to 10, 2008 in Dallas, TX.
>
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