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BGA Site Modification - Is It Possible?
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Authored By:Andy Price, Peter Vigneau Circuit Technology Center Inc. Haverhill, MA USA TranscriptBGA rework is a topic about which volumes have been written, and in most cases the focus has been on component removal and replacement. However, equally important is the topic of BGA site modification, and the need for such modification arises often. A common type of BGA site modification is the need to add a jumper wire at the BGA site. One option, of only a few, is to run a jumper wire through a hole in the circuit board. This method is used when there is a buried via, and other methods of terminating to the opposite side are not an option. This method also requires a high degree of operator skill, as well as precision milling equipment. It's fairly complex, and must be done correctly. The procedure begins with removal of the BGA component. If all goes well, the next step is to remove solder mask from the via pad terminating to the subject BGA pad. Next you mill a hole through the circuit board at predefined coordinates using a precision drill system and end mill of the appropriate size. Remember that although both power and ground planes may be cut, cutting inner layer signal traces must be avoided. Next you insert an appropriately sized Teflon sleeve into the milled hole. This sleeve will insulate the new conductor and prevent shorting to the inner layers. Now you select a flat, ribbon shaped, circuit track that will be inserted through the Teflon sleeved hole. These pure copper replacement circuit tracks are available in many sizes. A typical size for this application may be 3 thousandths of an inch thick by 15 thousandths of an inch wide. Now insert one end of the circuit track into the plated hole or via connected to the BGA pad. Then insert the opposite end through the Teflon sleeve. Apply a small amount of liquid flux and lap solder the circuit track to the plated hole connected to the BGA pad. To complete this part of the procedure you need to thoroughly clean the area and follow by coating the top and sides of the new circuit with high strength epoxy. The epoxy insulates the new circuit while bonding it to the circuit board surface. Finally turning to the other side of the board, solder a jumper wire to the exposed circuit track and then route and terminate the jumper wire as needed. This procedure is a bit elaborate, but one option to consider when no other is available. For more information visit: http://www.circuitrework.com/features/614.html |
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