>>> "Guy Ramsey" <[log in to unmask]> 09/19/01 12:00PM >>> IPC workmanship standards do not allow end overhang on this type of component. This is because the endpoint fillet gives much of the strength to the connection. A leadless component stacked on top of another leadless component will have end overhang. It will be weak. The connection to the board on the bottom component will see the mass of the component stacked on top of it. IPC-D-275 and IPC-2222 are design guidelines. It would not be a good practice to design with the intent of using this type of modification. Consider the CTE mismatch the bottom component will see. Top to bottom. Will both components heat the same? Will the board expand at the same rate as the component on top? Guy Ramsey Senior Lab Technician / Instructor E-Mail: [log in to unmask] <mailto:[log in to unmask]> Ph: (610) 362-1200 x107 Fax: (610) 362-1290 -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Jack Crawford Sent: Tuesday, September 18, 2001 1:17 PM To: [log in to unmask] Subject: Re: [TN] Piggy Backing of passives...Why one should go for addtional fab spin? >>> Ken Patel <[log in to unmask]> 09/18/01 11:06AM >>> All, What are the major reasons for not allowing piggy backing of the components? I know IPC-D-275 and it's replacement does not allow. I know there will be an additional rework cost but if the board is laid out and then engineering comes out with ECN that requires piggy backing of components -People here want to avoid costly fab spin on relatively low volume? There shall be some good quality and reliability reasons which I would like to know. re, Ken Patel. ---------------------------------------------------------------------------- ----- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 the following message: SET Technet NOMAIL 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 ---------------------------------------------------------------------------------