All,
Thanks to all that replied. As it turns out, there was a slightly different reason for wanting to do this operation, but the answers are the same. Just to keep you from wondering why, it was to remove the board thickness tolerance from the board where the connectors mount. Like doing controlled depth drilling, the back side of the board is mounted against a boss. The top of the board where the connectors mount can be up or down based on the board thickness which is about 10% of the board thickness. By drilling the locations of the connector mounting holes to a controlled distance from the back side of the board to the connector mounting surface, it removes the board thickness tolerance. Not sure if this helps in the visualization process, but... :-)
Later...
Scott Decker – Senior Analyst, Drafting & Design Services CID+ – Electronic Systems Center
UTC AEROSPACE SYSTEMS
3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.
Tel: 602 308 5957 FAX: 602 243 2347
[log in to unmask] www.utcaerospacesystems.com
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer - EXT
Sent: Monday, August 22, 2016 11:18 AM
To: [log in to unmask]
Subject: Re: [TN] [External] Re: [TN] Spot Facing areas for mounting hole of connectors.
Hi Scott-
I agree with Dean's suggestion, not for his reasoning, but because the answer to your question is that the laminate machining will need to be done at a machine shop. And that will mean more abuse/risks you're exposing the board to, and a fixture needs to be made to do it. So why not just make a fixture for the connector and remove the bosses?
BUT, theoretically:
I'm just getting into Class 3, so forgive me if I'm missing something, but there seems to be no IPC requirement for sealing board edges, which also have laminate exposure. As long as you maintain the same distance from the machining operation to conductors as Class 3 requires from board edge to conductors/vias, you should still be OK. (I'm sure Dean will straighten me out if I'm not looking at the right spec!)
Another potential problem is that those bosses are put there for a reason. Possible reasons:
-allowance for inspection of solder joints from both sides of the board -prevent conformal coat from gluing the connector down (could lead to trouble in thermal cycling test) -allowance for cleaning contaminants (failure to pass surface ionics after cleaning)
Can't think of any other concerns at this time.
Good Luck!
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, August 22, 2016 7:57 AM
To: [log in to unmask]
Subject: Re: [TN] [External] Re: [TN] Spot Facing areas for mounting hole of connectors.
It would be better/easier to simply sand off .010" from the bosses on the bottom of the connector, rather than exposing the fiberglass weave on the PWB. Any hole in the PWB that is not sealed will allow moisture inside the entire PWB. FR-4 weave is just like a sponge.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Decker, Scott UTAS
Sent: Monday, August 22, 2016 9:37 AM
To: [log in to unmask]
Subject: Re: [TN] [External] Re: [TN] Spot Facing areas for mounting hole of connectors.
John / Wayne, <--(John Wayne? ☺ )
The connector is a through hole mount and is a custom circular aircraft type 38999 if you are familiar with that type. It has 4 mounting bosses that make contact to the board and it’s those 4 areas that we are thinking of machining down on the board. Again, the amount is only around .010” or so and as John mentioned, I was also concerned about moisture getting into the weave areas and wicking into the board. I don’t believe it would get far and the areas are free of routing and any copper features, so I’m not too overly concerned, but that’s why I’m asking the group. Maybe I’m missing something and don’t know it… ☺ The other question will be if a board shop or will it need to be a machine shop that can do the operation if we go that way. I’ll pose that to our suppliers and see what I get from them. Thanks for the replies and I look forward to more info.
Later…
Scott Decker – Senior Analyst, Drafting & Design Services CID+ – Electronic Systems Center UTC AEROSPACE SYSTEMS
3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.
Tel: 602 308 5957 FAX: 602 243 2347
[log in to unmask]<mailto:[log in to unmask]> www.utcaerospacesystems.com<http://www.utcaerospacesystems.com/>
CONFIDENTIALITY WARNING: This message may contain proprietary and/or privileged information of UTC Aerospace Systems and its affiliated companies. If you are not the intended recipient please 1) do not disclose, copy, distribute or use this message or its contents, 2) advise the sender by return e-mail, and 3) delete all copies (including all
attachments) from your computer. Your cooperation is greatly appreciated.
This Document Does Not Contain Export Controlled Technology Or Technical Data.
From: John Burke [mailto:[log in to unmask]]
Sent: Friday, August 19, 2016 8:05 PM
To: TechNet E-Mail Forum; Decker, Scott UTAS
Subject: [External] Re: [TN] Spot Facing areas for mounting hole of connectors.
If you machine into the weave you clearly have a potential for moisture ingress???
Did you consider a jig and machine the bosses?
Best regards,
John Burke
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