Well drilling is not my thing either, but doing the mechanics the idea that .0014" thick (1oz) typical, of copper can even affect the drilling is a stretch, the total glass is about .060 thick and is stacked up many boards thick at a time in drilling. Glass is harder and much more damaging to metal drills that very thin copper films. Also the gumming of the epoxies loading the bits would affect the drilling. All of this can be accounted for in the (hit count) on bits and they are change automatically. The amount of copper thickness provided by the inter layer planes is very little compared to the other materials. However it does make for stress risers at their intersection with the hole plating. Another place you can see the stress risers starting cracks is on the "knee" if the PTH, there is a pad there with plating flowing over it. The thickness of 2 sided boards is relative and can be .015 to .125 easily the same as MLBs. Maybe Susan M. @ Robisan can way in, or Werner can set us all strait. "Hinners Hans M Civ WRALC/LUGE" <[log in to unmask]> on 01/15/2002 11:43:34 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to "Hinners Hans M Civ WRALC/LUGE" <[log in to unmask]> To: [log in to unmask] cc: (bcc: Warren Crow/US/I-O INC) Subject: Re: [TN] Remove unused "dead" pads on internal layers Hey Warren, Granted, Drill isn't my specialty but I've always heard that additional pads in the drilled stack can help. I'll hazard a guess, since Coombs isn't readily available, the additional metal gives the bit something to dig into being softer than the surrounding glass fiber & epoxy resin. What would be the benefit of softer layers in a drill stack? Could that improve hole wall quality? Reduce drill wander/wobble? I'm assuming the right feed, speed and chip load have been used. Somebody steer me in the right direction here - I'm learning. Obviously, a double sided board doesn't have inner layers and they tend to be a bit thinner than the high layer count boards I'm used to processing. Hans Integrity First - Service Before Self - Excellence in All We Do ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hans M. Hinners Electronics Engineer Warner Robins - Air Logistics Center (WR-ALC/LUGE) 226 Cochran Street Robins AFB GA 31098-1622 mailto:[log in to unmask] Com: (478) 926 - 5224 Fax: (478) 926 - 4911 DSN Prefix: 468 -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Tuesday, January 15, 2002 11:50 AM To: TechNet E-Mail Forum.; Hinners Hans M Civ WRALC/LUGE Subject: Re: [TN] Remove unused "dead" pads on internal layers Actually the cracked vias I have witnessed in the inter barrell tend to start at the intersection of the copper planes. A corner or stress riser starts the crack during thermal shock tests. Don't understand how the extra non- connected pads could help barrell, if so then there is no hope for a 2 sided board. "Hinners Hans M Civ WRALC/LUGE" <[log in to unmask]> on 01/15/2002 07:40:50 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to "Hinners Hans M Civ WRALC/LUGE" <[log in to unmask]> To: [log in to unmask] cc: (bcc: Warren Crow/US/I-O INC) Subject: Re: [TN] Remove unused "dead" pads on internal layers Hi Patrick, As others have said, I don't think the class of board matters for "unused" pads. It all depends on what your procurement documentation states, are you building to drawing or is there a clause that says process improvements that do not affect functionality are permissible. "Are they really unused pads?" They may be electrically nonfunctioning but they are there for a reason - better lamination quality (avoiding low pressure areas or excessive prepreg flow), better hole wall quality, better plating quality (esp. for any isolated traces), reduced loading of your etch solution or better thermal loading during assembly. Hans Integrity First - Service Before Self - Excellence in All We Do ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Hans M. Hinners Electronics Engineer Warner Robins - Air Logistics Center (WR-ALC/LUGE) 226 Cochran Street Robins AFB GA 31098-1622 mailto:[log in to unmask] Com: (478) 926 - 5224 Fax: (478) 926 - 4911 DSN Prefix: 468 -----Original Message----- From: Patrick Lam [mailto:[log in to unmask]] Sent: Friday, January 11, 2002 5:12 PM To: [log in to unmask] Subject: [TN] Remove unused "dead" pads on internal layers Hi TechNetters, For class 3 boards, is it acceptable to have unused pads removed on interanal layers. Thanks, Pat This e-mail may contain SEL confidential information. The opinions expressed are not necessarily those of SEL. Any unauthorized disclosure, distribution or other use is prohibited. If you received this e-mail in error, please notify the sender, permanently delete it, and destroy any printout. 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