Hi TechNet pals , I just joined this mail forum today - Thanks to Joe Fjelstad for letting me know about this forum at the recent PCB ASIA lectures in Penang - Hi Joe ! ; Based on the understanding I have of the flexible circuits manufacturing processes , I have the following comments/queries : I hope these have not been discussed in this forum before ! Pad registration accuracy on flex circuits has always been an issue. Pads are often defined by the coverlay opening (COVERLAY DEFINED PADS ) rather than by the pad itself (RESIST/METAL DEFINED PADS).Coverlay defined pads are necessary to hold down the pads to avoid the peeling-off effect. For a pad which is defined by the coverlay opening , accuracy of the EXPOSED pad location with respect to the fiducials is lost due to the running out of the coverlay opening. Coverlay hole punching errors , as I understand , are due to a) punching tool accuracy b) stack up tolerance errors as the punch moves along punching the various pad locations . The resultant effect is that the paste is printed as per the gerber file (ACTUAL METAL LOCATION WITH RESPECT TO FIDUCIALS) while the actual EXPOSED pad location is off due to the shifted coverlay opening.This will cause errors in the relative location of the EXPOSED pad,the part and the paste - resulting in tombstone / solder defects. The above effect magnifies as we go to small parts such as 0603 (or 30x60) and 0402 (or 20x40) parts . Based on the above experience,following are my queries : 1) Any comments on the above problem ? 2) As a flex manufacturer, what is the BEST pad location accuracy with respect to the fiducial can one offer for COVERLAY DEFINED PADS ? How ? What are the current capabilites in the market ? Where are these capabilites available ? 3) Have any of you had good/bad experience of assembling 0603 & 0402 size components on flexible circuits ? If yes, would you share the following details ; - Pad dimensions & geometry for such parts - Flex pad design rules/requirements for such pads for a satisfactory soldering of such parts. 4) Are there any IPC standards for the above ? 5) As a flex assembler , would process engineers like to share their experience of assembling such parts ? Thanks in advance , _______________________________________________________ VISWANATHAN A/L NARAYANA IYER aka Vishy Staff Engineer - AMT/SMT Department, Energy Systems Group,ACCES Motorola Technology Sdn.Bhd., Penang , Malaysia Phone / Voice Mail : (604) 8503566 Fax : (604) 6442277 Paging center : (604) 8504223 - Pager: 381 > mailto:[log in to unmask] _______________________________________________________ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################