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Method for glued BGA or LGA socket and backplate

IP.com Disclosure Number: IPCOM000020157D
Publication Date: 2003-Oct-29
Document File: 5 page(s) / 291K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for glued ball grid array (BGA) or land grid array (LGA) socket and backplate. Benefits include improved functionality, improved performance, and improved cost effectiveness.

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Method for glued BGA or LGA socket and backplate

Disclosed is a method for glued ball grid array (BGA) or land grid array (LGA) socket and backplate. Benefits include improved functionality, improved performance, and improved cost effectiveness.

Background

         Sockets for BGAs and LGAs are typically used in reference design vehicles and silicon design, debug and validation. Sockets are used so that one circuit board can be used with two or more different silicon devices intermittently. This approach enables one board and two silicon devices to be used where two boards with different silicon devices would be required.

         Sockets enable new revisions of silicon devices to be swapped with older versions in existing board designs. Sockets designed for larger BGA and LGA package sizes require strong mechanical mounting mechanisms. They hold the socket to the board and compress the BGA or LGA package against the socket interface material onto the board. These compression mechanisms usually include screws, clips, or cam devices, which require large holes in the board immediately surrounding the BGA or LGA footprint. These holes take area away from the PCB areas typically used for trace routing. A socket body attached to the PCB using an adhesive enables more of the board area around the socket/BGA/LGA footprint to be used for trace routing.

         There are three major commercially available socket types that are used in these applications. The first socket type is the SMT Socket/Adapter combination. This system requires the BGA or LGA to be soldered to an interposer. The interposer with pins is then inserted into the socket which is soldered to the PCB using an SMT process. The major disadvantage of this socket type is that the inductance of its construction is relatively high (1.0 - 2.5 nH at 1 GHz) due to the long physical length of the connection between the BGA ball and its corresponding land. The adhesive mounted socket design would not have this problem because we could include a lower inductance interface material in its design (see Figure 1).

         The second socket type is the elastomer with screw or clip fasteners. These sockets typically have much shorter BGA ball to land distances. This can lead to much lower inductance (0.02 – 0.4 nH). Unfortunately, to electrically engage these commercially available elastomer sockets, high compressive forces are needed (20-40 gram/ball). Commercially available elastomer sockets use holes in the board and screws to compress the BGA between a compression plate on the BGA side of the board and a backing plate on the opposite side of the board. Backing plates are required particularly if the BGA or LGA package is larger than 35 mm x 35 mm (see Figure 2).

         The third socket type is an SMT socket plus compression engagement mechanism. These sockets mount to a PCB using an SMT reflow process. The internals of these sockets vary from elastomers to pogo pins, to springs. Again, compression is required to engage the BGA. This is...