Being very interested in the use of nonfunctional pads in PCB designs, from a manufacturability point of view, I concur with other fabricators: Nonfunctional pads are undesirable Specifically in regards to machineability in the drilling process. However, my main concern is the increased propensity for tool breakage on small holes. I have not found the Cu to induce additional tool wear, conversely, that the glass substrate is more abrasive on the carbide. Also, I am curious as to what interconnect-reliability issues are associated with the presence of nailheading, in and of it's self. Dan Buxton _____ /____/\ _______|___ \/| /________ /_| |< Continental Circuits Corp. / ______||_ </| 3502 E.Roeser Rd. | / | /___| |/ Phoenix, AZ 85040 | | |___|_____/ Voice(602) 232-9133 Fax(602) 268-7386 | \/_____ /| E-Mail [log in to unmask] \_________|/ ______________________________ Reply Separator _________________________________ Subject: Re: Removal of non-functional pads Author: [log in to unmask] at INTERNET Date: 06/27/95 4:47 PM The issue of the need for non-functional pads has been a matter of some controversy for at least 20 years. AT&T originally asked designers to include them on all layers. Studies of PTH failures following multiple solder shocks (up to 100 or more) showed better life with non-fuctional lands. Apparently replacing epoxy with copper reduces the Z-axis TCE and associated barrel strain. However, as plating technology has improved, the issue of PTH failures during soldering has become a low level concern, and the need for reduced barrel strain has dropped. At the same time, it was recognized that drilling through copper generates significant heat. We have found that problems like nail-heading, drill wear, pink ring, and defective hole walls are much worse with non-functional lands. Consequently we have moved away from the use of non-functional lands. For at least 10 years the majority of our product has been made without non-functional lands. Bellcore accepts these designs as reliable. I know of no field problems attributed to the lack of non-functional lands. The only problems, that ever occur are on the old designs that still have non-functional lands. These designs occasionally cause process problems at drill that lead to PTH quality issues. In conclusion, I have no specific reliability studies to point to, but our experience has shown that the omission of non-functional lands causes no customer reliability problems and does lead to a more processable board with better quality holes. Bob Holmes AT&T ------------- Begin Original Message ------------- Message-Version: 2 From: smtplink.dsccc.com!jbaumgar Date: Mon Jun 26 14:03:28 CST 95 Received: from attme by attme.cnet.att.com; Mon, 26 Jun 1995 18:06 EDT Received: from att!wwa.com!ipc!ipchq.com by ig2.att.att.com id AA12931; Mon, 26 Jun 95 18:06:05 EDT Received: by gw2.att.com; Mon Jun 26 17:36:22 EST 1995 Received: from ipc by gagme.wwa.com with uucp Received: (Smail3.1.28.1 #8) id m0sQLn8-000FObC; Mon, 26 Jun 95 16:34 CDT Received: by ipchq.com (Smail3.1.28.1 #2) Received: id m0sQLD3-0000GqC; Mon, 26 Jun 95 15:56 CDT End-of-Header: Email-Version: 2 Subject: Removal of non-functional pads Resent-Date: Mon, 26 Jun 95 14:03:28 CST Old-Return-Path: <miso!smtplink.dsccc.com!jbaumgar> Message-ID: <[log in to unmask]> To: [log in to unmask] Resent-Message-Id: <"B8tYs1.0.9R9.7ynxl"@ipc> Resent-From: [log in to unmask] X-Mailing-List: <[log in to unmask]> archive/latest/618 X-Loop: [log in to unmask] Precedence: list Resent-Sender: [log in to unmask] End-of-Protocol: Content-Type: text Content-Length: 640 Bellcore TR-NWT-000078 in paragraph 6.2.1.2.4 recommends that non-functional pads exist on every conductor layer. Yet all CAM systems have a non-functional pad removal function. Some board manufacturers use this functional automatically Most board shops, I think, would like to use this function. My question: Does there exist a statistically significant study on the reliability of boards that do not have the non-functional pads? If so, is this study published? Regards, Jamie Baumgart, DSC Communications [log in to unmask]