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90 SMT007 MAGAZINE I JANUARY 2018 attempted with customer-approved materials and methods. Like all repairs defined by the IPC 7711/21 Rework of Electronic Assemblies/ Repair and Modification of Printed Boards and Electronic Assemblies, the repairs can only be done with customer approval. There are two different industry-accepted repair techniques for lifted pads when the objective is to replace the pad. One involves the use of dry film heat and pressure curable adhe- sive that is stuck to the replacement pad. The second involves the use of a two-part epoxy and "gluing" the replacement pad to the lami- nate. While the better method usually involves personal preferences, pull test data and better observed results of the replacement pad stay- ing in position post soldering makes the epoxy method the one of choice. The epoxy repair technique outlined in IPC-7721 Rev C Procedure 4.7.1, describes a method for the repair of pads by using a replacement plated pad (attached via a skeleton of other patterns) and a two-part epoxy adhe- sive system. Each of the steps in the process require clean- ing for best possible adher- ence of the repair materials as well as well as for inspec- tion to make sure that the procedure is done properly. To start, remove the pad with a sharp knife and care- fully cut a small piece of the connecting circuit. Using the proper solder and flux, There are a variety of reasons behind pads getting "lifted" completely or partially from the laminate of a PCB. Per the just revised IPC-A-610 Revision G, a defect for all three classes occurs when the land is lifted up one or more pad thicknesses. Lifted pads can occur when a device has been improperly removed or there is a manufacturing defect in the board construction. The propensity for this to occur when pads are very small, like in the case of an 0201 or when there is an uncon - nected BGA pad. In any case, as with any repair, the ultimate decision on the ability to repair the pad lies with the customer. In some cases, only a limited number of repairs are allowed by the customer and if allowed the same repairs can only be Knocking Down the Bone Pile Column by Bob Wettermann BEST INC. PCB Pad Repair Techniques Figure 1: Initial damaged pad requiring replacement.

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