Collins, This is a GOOD topic for discussion. I have notice that even the PCB pad size does not match the TO252 foot print. The lead parameters are about the same size as the PCB pads. My biggest concern is the wetting of the Thermal heat sink bar with different PCB foot print layout. We conduct a lot of x-ray imaging to ensure adequate wetting. I will keep out a look for info on this topic. Victor, -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Collins Graham Sent: Friday, March 12, 2004 2:28 PM To: [log in to unmask] Subject: [TN] solder fillet requirements for a TO-252 style part, class 3 assy. Good day TechNet! We are having a debate about the solder fillet requirements on TO-252 style transistors, in a class 3 SMT application. I'm wondering where the experts on TechNet sit on this one. An example of the type of part I'm talking about can be seen at this link: http://www.onsemi.com/pub/Collateral/418B-04.PDF There are two types of attachment on this part, the ground pad and the leads. We have treated the ground pad as per IPC-A-610 section 12.2.9, "flat lug leads". This part of the attachment is not controversial. What is being debated is what rules should apply to the other leads. Physically they are gull wing formed leads, but they are very thick. So - do the requirements of 12.2.5 "flat ribbon, L, and gull wing leads" apply to these? In particular, the heel fillet must be up at least the equivalent of the lead thickness. We've been meeting this requirement, but not without pain, and I'm wondering if we need to meet this. On a lighter component (e.g. a SOIC, where the lead thickness may be say 10 thou) this height requirement is pretty trivial to meet, but on one particular part I'm looking at the lead thickness is 18 - 25 thou. So - specifically - would you agree the height requirement for this particular style of component is that the heel fillet be at least 1 lead thickness high (plus dimension G, the gap between bottom of lead and the pad) per 12.2.5.6? Am I missing something in the spec? Have a good weekend! regards, Graham Collins Process Engineer, Northrop Grumman Canada Corporation Halifax (902) 873-2000 ext 6215 --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------