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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