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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