I kinda like these thoughts from Lamar.
1) When I think of potting, I assume that the electronics is put into
some sort of mould or box, which is filled with a material or potting
compound. The potting box can be left as part of the assembly or removed
later; it either case you end with an assembly which is totally immersed
in a block of polymer.
2) Coating is a (relatively thin) layer which covers all or part of the
assembly. I would agree with Lamar's distinction of using the bounds of
IPC-CC-830 to define this.
3) Ask the man on the Clapham omnibus whether the example described in
the first paragraph is totally encapsulated, and he would say yes. But
our use of the word encapsulant is for things like glob-tops - a dome of
material (thicker than conformal coating) which is used for protecting
COB, wire bonds, flip chips, LEDs and other sensitive components. I
would say encapsulants are characterised by being thicker than conformal
coatings, and often applied more selectively. Not the same as potting
There is a book by Martin Bartholomew called Encapsulation and Underfill
Technology (http://www.amazon.co.uk/exec/obidos/ASIN/090115038X/1774),
but I'm not sure how easy it is to get hold of these days.
If you think about components as opposed to pcb assemblies, then
meanings can diversify - thinking about coils which have been vacuum
impregnated (potted) or dipped capacitors (encapsulated).
An interesting exercise - hope you can achieve a consensus. Otherwise, I
suggest we all revert to calling everything "goop".
Peter
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Lamar Young
Sent: 04 June 2009 21:20
To: [log in to unmask]
Subject: Re: [TN] Coating, Encapsulation, and Potting
I was going to comment only on #3, but curiosity won and I had to pick
up some books.
1. When I think of potting, I think of electrical ballasts (like
mentioned a couple days ago, trying to remove the tar/pitch). Potting
materials encapsulate, but I don't consider encapsulants as potting
materials. Potting is more a 'gross' application, such as dispensing
grams of material to fill up a housing. Encapsulants are finer
controlled dispensing material in only specific isolated areas.
2. I'm not aware of any IPC definition. But, in Plastics Materials and
Processes by Charles Harper and Edward Petrie the section on
Encapsulation starts with "Encapsulation (also called potting) ...".
In another book by Charles Harper, Electronic Packaging and
Interconnection Handbook, encapsulation is defined as "Completely
enclosing a component in a coating of a viscous resin system by dipping,
spraying, or embedding with or without a mold. The coated component is
usually irregular in shape." Potting is defined "Similar to embedding,
except the mold (can or case) remains a part of the system." Embedding
is defined as "Surrounding a part or component positioned in a mold with
a liquid resin system, curing the resin, and removing it for use."
3. If the thickness is greater than that specified in IPC-CC-830 (or
MIL-I-46058C), then I'd move from the conformal coating group to the
encapsulant group. For example, 8 mil of a silicone could still be
considered a conformal coating, 10 mil would be an encapsulant.
4. Underfills are outside my area of expertise. But, I don't see how
they could be classified as any of the mentioned. I saw underfills
referenced in Plastics Materials and Processes as an electronic plastic.
Lamar
Douglas Pauls <[log in to unmask]> Sent by: TechNet
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06/04/2009 02:33 PM
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Subject
[TN] Coating, Encapsulation, and Potting
Good afternoon all,
All this talk of underfill sparked a reminder of an IPC action item of
mine. Unknownst to most of you , I signed you all up on some of my
committees. There will be a new task group addressing potting and
encapsulation, which will meet at the Fall IPC. We already have
conformal
coat task groups.
So, I wish to initiate a series of questions and illuminating debate.
Pardon me if I fall short on the illumination part (leave it alone
Dewey).
1. What would you consider to be a definition of "potting" and a
definition of "encapsulation"?
2. Are there standard definitions for these somewhere? They don't
exist
in IPC as far as I know.
3. What would you consider to be the boundary between conformal coating
and "potting or encapsulation"? I have my own opinions but want to hear
yours.
4. In what class would you consider an underfill to be in?
That's enough homework for now.
Doug Pauls
Rockwell Collins
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