Techies
I thought I would share some info that, I feel, is relevant to this
question.
Albeit some time ago, my company supplied a dip coating system to a
major automotive electronics manufacturer who were using a silicone
conformal coating.
So what, you might say?
Well, we found that, despite an 8 hour bake at around 80DegC, the
residual/accumulated moisture "entrapped" into the assembly, was
sufficient to kick-over the moisture sensitive coating.
So what? Well, this meant that the coating remaining in the dip tank -
some 60 litres (15.85 gallons = US Term) - had to be disposed of every
2 weeks (Fortnight = British term!)
3 issues:
1 = Environmental impact in the disposal of 60 litres of product every
2 weeks.
2 = Cost impact of same
3 = How come the bake was not able to eliminate this problem?
So - I hope the new document might yield some recommendation as to the
minimum baking time to avoid this phenomenon.
Thinks - maybe I need to spell that Fenomenon rather than
phenomenon....? [thinks - I am somewhere framed on the walls of Mr
Pauls....] (Dewey - that rhymes, sorry, rimes? Excuse me, Rymes?) Ah!
What the heck.
Graham Naisbitt
On 28 Aug 2008, at 17:45, Joe Macko wrote:
> Denny,
>
> We have always treated FR4 PCBs as moistures sensitive and baked them
> out before reflow to be safe. Everyone has there own idea about bake
> out
> time and temperature and most CMs do consider the PCB moisture
> sensitive. We bake for 5-6 hrs at 110 C. Boards are generally used
> within 2-weeks of bake out.
>
> Best Regards,
> -joe
>
>
>
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> From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
> Sent: Wednesday, August 27, 2008 7:10 AM
> To: [log in to unmask]
> Subject: Re: [TN] Moisture in PCB Assemblies
>
> Bill,
>
> There has been some speculation that with the higher assembly
> temperatures of lead-free, that PCBs should have a Moisture
> Sensitivity
> Level - just like the components being mounted on them.? However, I
> don't think JEDEC will step up to the plate to adopt anything to do
> with
> PCBs.? So, it would be the job of the IPC to do that.?
>
> With the upcoming IPC meeting in late September, Schaumburg,
> Illionois,
> now would be a good time to debate the need for circuit board MSL
> levels. As pointed out, the group working on Storage and Handling will
> go a long way, but moisture absorbsion propensity is also a property
> of
> the resin/glass composition of the board.?
>
> How about it TechNetters?
>
> Denny Fritz
> MacDermid, Inc.
>
>
> -----Original Message-----
> From: [log in to unmask]
> To: [log in to unmask]
> Sent: Tue, 26 Aug 2008 7:19 pm
> Subject: [TN] Moisture in PCB Assemblies
>
>
>
> Fellow TechNetters:? I was asked a question by a valued customer if
> there is any
> other references made to moisture in raw PCBs and populated assemblies
> other
> than the J-STD-033 and also the IPC rework standards.? I've looked in
> IPC
> Standards I have on file however I could not find any
> references/guidlelines at
> all.? Can anyone out there shed some light on this???
>
> I thank you folks in advance for your efforts on my behalf.
>
> Bill Black
> Medco
> Q.A. Manager
> Tel:? 631-667-9699
>
> E-Mail:? [log in to unmask]
>
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