Doug
I'll not reply on the formal part but I will reply to your paragraph 2).
As you state, conformal coating is primarily to protect against moisture
and crud. With reference to your other optimistic wish-list, it is more
usually negative than positive.
Shock and vibration: ideally, the coating, if it be truly conformal
(I'll mention Parylene as the classic example of one) will hardly make a
jot of difference in this respect. If it not be truly conformal and
underfills components, then any shock and/or vibration transmitted to
the substrate will also be transmitted to the components without
attenuation. This is especially true of silicone coatings, which will
transmit a shock wave like a hammer.
Thermal emissivity: if the coating has any significant thickness, it
will insulate, to some extent, therefore it is reasonable to assume that
there may be a ***small*** rise in temperature of dissipative components
when they are coated. This will not be of general importance. What may
be of importance is, again, with underfilled components which are
dissipating power. This will cause the underfill to expand, with a TCE
greater than that of the solder joints and leads, potentially causing
the solder joint to take the stress. The resultant strain, especially if
cyclic, may lower the joint reliability.
Moral of the story: make sure that conformal coatings are truly
conformal, with no underfilling.
Hope this helps,
Brian
[log in to unmask] wrote:
>
> Good morning all,
>
> I hope you all had a nice weekend.
>
> Last week (and a few weeks preceding) I have been part of a group that is
> examining our conformal coating process looking towards the future. Right
> now, I am in the middle of a classic engineering vs. manufacturing head
> butting exercise. For some of our engineers, manufacturability seems to be
> a completely foreign term.
>
> I have been tasked to gather information. I figure this group is a great
> place to start. I have two basic questions:
>
> 1) What specifications do you use to determine if you have a "quality"
> coating in production? Internal workmanship standards? IPC-A-610?
> MIL-STDS? I'm not talking about MIL-I-46058 or IPC-CC-830, since those are
> primarily procurement documents.
>
> 2) Can you give me references for papers on the engineering aspects of
> conformal coatings? Our engineers claim benefits like added vibration
> resistance, thermal emissivity, etc., in addition to the usual moisture and
> crud barriers.
>
> Thanks in advance.
>
> Doug Pauls
> Rockwell Collins.
>
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