My thanks to all of you for your responses. That is exactly the kind of mix I hoped to receive. And, yes Richard, I did read your post before I asked for more definition - if there is one. What I gather by the varied responses I received is that there is no consensus. It definitely appears to be a customer decision that needs to be in the SOW, based on the supposition that they know their product better than any of us do (except for those of you who are lucky enough to work with the same design groups internally). It's a little tougher for those of us who work with a myriad of customers that have varying knowledge of these issues.
I'm going to take another tack by suggesting that this really doesn't appear to be much of a problem as the automated coating machines for sale typically do not include options for doing the edges of the boards. If there was a major outcry for this function, I would think some would offer it. I assume that this is a rather rare problem that may become more of a problem as more coating machines are used instead of the old dip coating or spray rig which just covered the edges as a part of the process. Now they don't automatically get covered. Will customers notice, or will they not? Will it become necessary to get a reading on this before you accept a new product for build? Definitely. If it's not a part of the new product introduction process for all of us, it may well become a necessity soon.
Thanks again for all of your feedback. I always know I can trust getting good advice from the experts here on TechNet.
Dale
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Tuesday, March 03, 2015 9:43 AM
To: [log in to unmask]
Subject: Re: [TN] Required Conformal Coating of Edges of PCB's
Hi Dale-
IMO what you've seen here is a great picture of what the situation is:
1. There is no regulation or standard requiring conformal coating of board
edges, and there shouldn't be. If the customer wants it anyway, they need to
mark up their documentation accordingly.
2. Any concerns related to the board edges should be handled as a laminate
damage problem, which conformal coating is not intended to fix. I believe
IPC has some reasonable standards for the repair of laminate damage, so
follow those if it's applicable.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dale Ritzen
Sent: Tuesday, March 03, 2015 10:07 AM
To: [log in to unmask]
Subject: Re: [TN] Required Conformal Coating of Edges of PCB's
Seriously folks... is this a real or imaginary problem? We have seen both
"yes" and "no" opinions over the last several days. Is anyone basing their
opinions on a specific standard that states what conditions require the PCB
edges to be coated, or is it simply a matter of the customer specifying that
requirement on their S.O.W. for the product? Are manufacturers to second
guess the customer about the places the product will be used and the
environmental conditions it will be placed in that might warrant coating of
the PCB edges, or does that really matter anymore with the state of the art
PCB manufacturing processes - regardless of the condition of the material
left on the edges (with the possible exception of PCBs made of Polyimide
materials)?
So far we have seen opinions - not quotes from any standard that covers
this. Does that exist, or is it something that the IPC technical committees
need to look into for further definition? Sounds to me like it needs some
definition in a standard so we all have something to march to...
IMHO,
Dale Ritzen, ASQ CQA
Quality Manager / ISO Management Representative ___________________________
Austin Manufacturing Services
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Yuan-chia Joyce Koo
Sent: Monday, March 02, 2015 5:20 PM
To: [log in to unmask]
Subject: Re: [TN] Required Confromal Coating of Edges of PCB's
also there are cut off edges of the PWB like using shear... really bad with
all the fiber glass stick out.... there is not enough coating can fix
that... (don't laugh, those are real surprise you get from far)...
jk
On Mar 2, 2015, at 10:04 AM, Stadem, Richard D. wrote:
> You lost me on that post, Wayne.
> Not sure what you are trying to describe when you talk about drilling
> thousands of overlapping holes as a method of routing out a PWB?
> The edge-coating being discussed was conformal coating, not plating of
> the edges?
> Sorry if I am slow on the uptick today.
> dean
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
> Sent: Monday, March 02, 2015 8:44 AM
> To: [log in to unmask]
> Subject: Re: [TN] Required Confromal Coating of Edges of PCB's
>
> I feel the need to point out the obvious:
>
> -Suppose we singulated a board by using a pcb drill, drilling
> thousands of overlapping holes. It's hard to keep drills sharp, so
> let's assume we just swap out bits after the same number of "hits"
> that we deem the bit good for via hole drilling. Now how 'bout we coat
> the exposed edge with plated metal, just to make sure that if there's
> a problem with the drilling/routing process, we have a real good
> chance of making a short.
>
> Any reason that should be dis-allowed? Try calculating the exposed
> area on the edge vs. all of the via circumferences you've got!
>
> Therefore, it's ridiculous to specify coating of routed board edges,
> which if anything, have less potential to damage fiber bundles than a
> drill. Snapped areas are a different category because drilling/milling
> has a limited capability to damage the laminate.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Monday, March 02, 2015 9:26 AM
> To: [log in to unmask]
> Subject: Re: [TN] Required Confromal Coating of Edges of PCB's
>
> Rich,
> In addition to what Dr. Pauls has detailed below, I also want to point
> out that whether or not any specification "recommends" or "does not
> recommend"
> coverage on certain areas of components and PWBs, it is the assembly
> drawing which has historically taken precedence over all standards
> when it comes to defining conformal coating coverage.
> This is because every assembly and PWB has different design
> requirements and it would be too difficult to document all of the
> exceptions to the different rules for each type.
> Many circuit boards are simply blanked out on a press, leaving exposed
> fiberglass edges, but these are also typically high-volume,
> low-reliability PWBs used only for consumer electronics. All other
> PWBs are typically routed or laser cut, and as Doug stated those are
> typically sealed by the singulation process. Depending on the type of
> PWB material, the method of singulation, and the application, there
> may be no need to coat the edges.
> Or there might be, but then one would expect this to be detailed as
> part of the assembly requirements on the drawing.
>
> dean
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
> Sent: Sunday, March 01, 2015 8:07 PM
> To: [log in to unmask]
> Subject: Re: [TN] Required Confromal Coating of Edges of PCB's
>
> Rich,
> MIL-I-46058 is simply a materials qualification document. It does not
> address the coating of board edges. I would disagree with Graham and
> I do not believe that conformal coating edges of boards is a value
> added process. Most boards in high performance electronics have
> routed edges.
> The routing process tends to smear the resin over the glass
> reinforcement, sealing the edges. And since most design standards do
> not allow internal circuitry closer than 25 mils from the edge of the
> boards, water or external contaminants would have to penetrate 25 mils
> of epoxy resin to get to circuitry. If the edges of the boards were
> sheared or snapped, where the resin did not seal the ends, then
> perhaps the sealing would be justified. I can say that Rockwell has
> coated some board edges and left other edges free.
> We have no field failure, ever, that can be traced to lack of coating
> the board edges.
>
>
> Doug Pauls
> Principal Materials and Process Engineer Rockwell Collins
>
> On Fri, Feb 27, 2015 at 10:51 AM, Richard Kraszewski <
> [log in to unmask]> wrote:
>
>> Does anyone recall which MIL document calls out the requirement to
>> cover the PCB edges of assemblies?
>> I have been led to believe that one exists but that more than likely
>> it is not MIL-I-46058C.
>>
>> Any thoughts??
>>
>> Rich Kraszewski
>> Plexus
>>
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