Hi, Lorraine, It's obvious that your designer has no mechanical sympathy whatever! Your question connects with a previous thread concerning removal or not of 'non-functional' internal pads during board fab. If you have a 3 thou interference on the finished hole diameter, the corner contact points of your pins to the hole wall are going to cut through the barrel plating and into the hole wall material itself. I doubt that you have more than 1 oz plated copper inside the holes = 1.4 thou (mils) per side, and you may even have 1/2 oz, which will make the situation worse, as the pins will be cutting through less copper and more substrate material. Until the holes are filled with solder, pre-heating and other thermal excursions will make the hole diameter contract, causing the pin corners to dig even further into the substrate material, which will damage it, though by how much is hard to say. There will be some local delamination as the material displaces to make room for the pins, and this delamination may spread further in time. The major damage, as I see it, will be to the hole plating. Apart from cutting through it, the shear stresses imposed on the interconnection between the hole plating and the different layers, caused by forcing the pins into the holes, stands a good chance of severing the connection. This may happen straightaway, or later if your boards experience resin recession, and it will be worse if non-functional pads have been removed from the internal layers, as there will be less mechanical support to resist the shear stresses. You might even find the combination of delamination and shear stresses causes surface pads to lift. I strongly urge you to take some cross sections of boards assembled in the manner you describe. You will see then what damage has been caused and can then present your designer with the findings. Peter "Reid, Lorraine" <Lorraine.Reid@TRI To: [log in to unmask] VIRIX.COM> cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Sent by: TechNet Aero/ST Group) <[log in to unmask]> Subject: [TN] connectors and hole diameters 02/01/02 06:45 PM Please respond to "TechNet E-Mail Forum."; Please respond to "Reid, Lorraine" Can anyone point me in the direction of any investigations into the potential for long term failures caused by inserting a thru-hole mounted connector into holes which are slightly too small to fit? We have a situation where a connector, with square pins, diagonal dimension 25 thou, is being inserted into plated holes, finished size 22 thou. The connector is then soldered. The connector pins can be forced in, but I am concerned about the potential for damage that may not appear immediately obvious. The board is 4 layer, so obviously there are connections from the holes to the inner layers. The obvious solution is to enlarge the holes (not possible for this batch), but the designer is unwilling to make changes unless we can prove that there is a genuine risk of failure of the interconnects due to forcing the connector into the board. Thanks in advance Lorraine Reid --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------