I'm manufacturing the boards for the customer. We use his parts, his board design and the specified flux. The SIR board I referenced is that used by all flux manufacturers to qualify their solder paste and liquid fluxes and is not a coupon on the assembly. The IPC specifies a conformal coat thickness of .003 to .1xx". I'll have to research the different conformal coating specs in light of what you said. We meet with the engineers from Humiseal last week relative to product selection; acrylic, UV cure and water based products. They stated that they are designed to protect electronic circuits from harsh enviroments, out side products and that is why Humiseal is specified on all military products.
 This is why I know that if we build and test the board here and coat them the resistance won't change and discharge their lithium battery. Currently we build, ship and they test.
Then they ship them out and return those that don't have an infinite reading across the battery or 3.3 to 3.1 volts on their 3 VDC battery. Baking the board on the returns at 60C (battery spec not to exceed 85C) has fixed many that didn't have bad batteries of a bad clock chip. Form now on we are testing the batteries before we put them in since I found 5 bad ones in the shipping container. The discharged batteries measure a resistance so it wasn't our boards in those cases.
Now I need more information on "Bloc" Moisture sensitive parts. My recommendation Friday was to have us perform the testing and then conformal coat the board within 24 hours. Based on what I've seen and not knowing what happens to the board when it leaves us, I feel this will solve the problem. It will certainly remove the unknowns if we control all the handling and process steps.
  Looking forward to your reply.


-------------- Original message -------------- 
From: Brian Ellis <[log in to unmask]> 

> Firstly, are the comb patterns tested from snap-off coupons from the 
> production PCBs? If not, you may have qualified the flux, but not the 
> combination of flux, components and production quality boards. Secondly, 
> do you think a 196 hour test would be representative of real-life 
> conditions over a few thousand hours? Thirdly, if I understand you 
> correctly, you have a flux residue porridge in contact with humidity 
> sensors, without knowing the hygroscopicity of said porridge. Fourthly, 
> I would be very cautious about conformally coating a) over humidity 
> sensors b) over potentially hygroscopic flux residue porridges and c) 
> over flux residues generally unless you have carefully qualified the 
> process (and you would need more than 168 hours testing time). Never 
> forget that conformal coating may be a moisture barrier, but it is never 
> a long term humidity barrier. 
> 
> I'm sorry, but only you can answer your questions in detail, by long and 
> careful systematic qualification testing. 
> 
> Brian 
> 
> John Goulet wrote: 
> > 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 
> process 
> > 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. 
> > 
> > --------------------------------------------------- 
> > Technet Mail List provided as a service by IPC using LISTSERV 15.0 
> > To unsubscribe, send a message to [log in to unmask] with following text in 
> > the BODY (NOT the subject field): SIGNOFF Technet 
> > To temporarily halt or (re-start) delivery of Technet send e-mail to 
> [log in to unmask]: SET Technet NOMAIL or (MAIL) 
> > To receive ONE mailing per day of all the posts: send e-mail to 
> [log in to unmask]: SET Technet Digest 
> > Search the archives of previous posts at: http://listserv.ipc.org/archives 
> > Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for 
> additional information, or contact Keach Sasamori at [log in to unmask] or 
> 847-615-7100 ext.2815 
> > ----------------------------------------------------- 
> > 
> 
> --------------------------------------------------- 
> Technet Mail List provided as a service by IPC using LISTSERV 15.0 
> To unsubscribe, send a message to [log in to unmask] with following text in 
> the BODY (NOT the subject field): SIGNOFF Technet 
> To temporarily halt or (re-start) delivery of Technet send e-mail to 
> [log in to unmask]: SET Technet NOMAIL or (MAIL) 
> To receive ONE mailing per day of all the posts: send e-mail to 
> [log in to unmask]: SET Technet Digest 
> Search the archives of previous posts at: http://listserv.ipc.org/archives 
> Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for 
> additional information, or contact Keach Sasamori at [log in to unmask] or 
> 847-615-7100 ext.2815 
> ----------------------------------------------------- 

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------