Phil,
From a prior life...
We baked boards prior to conformal coat at 100C to 125C for a minimum of 1
hour.
This is one subject we did much work at and did not write a paper. Speaking
from memory, we exposed various board materials to moisture and weighed
them. Then, we baked the boards for a given period of time and weighed them
again at a specific temperature. Discovered that the weight difference after
baking the boards out for more than 1 hour at 100C to 125C was minimum. For
moisture sensitive material, like polyimide, suggest baking the hardware for
2 hours minimum.
Of course, at higher temperatures, you can remove the moisture faster, but
the price you might pay is thermally shocking the hardware and the boards.
At lower temperatures, you may be safe if you bake them overnight.
Concerning reliability, don't have an answer for you. We did not have a
problem with component or board reliability after baking the hardware at
100C to 125C for 1 hour. It depends on your components and board materials.
Hope this helps.
Good Luck.
Lee Whiteman
Senior Manufacturing Engineer
E-Mail: [log in to unmask] <mailto:[log in to unmask]>
Ph: (610) 362-1200 x208
Fax: (610) 362-1290
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Phil Nutting
> Sent: Monday, April 08, 2002 12:13 PM
> To: [log in to unmask]
> Subject: [TN] Bake before Conformal Coat
>
>
> Good day, Technet
>
> After reviewing past threads regarding baking boards before
> conformal coating I come up with quite a varied selection of ideas.
> I found 1 hour @100°C, 4 hours at 150°C, and 4-5 hours at 125°C.
> My design engineer is concerned about the boards being exposed to
> this temperature for an extended time. Yes, in the wave solder it
> sees much higher temperatures... for a short period of time. Our
> aqueous wash system dries at about 65°C for 20 minutes.
> Our product normally is tested to 40 - 50°C depending on the
> customer needs.
> The past threads suggested raising the temperature above 100°C to
> "boil off" any remaining water.
>
> Can this time/temperature be narrowed down any?
>
> And if we use a lower temperature are we possibly trapping moisture?
>
> How will the reliability be affected by these elevated temperatures.
>
> Thanks in advance,
>
> Phil Nutting
>
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