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Method for a surface-mounted LGA socket contact

IP.com Disclosure Number: IPCOM000012931D
Publication Date: 2003-Jun-11
Document File: 3 page(s) / 102K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a surface-mounted land grid array (LGA) socket contact. Benefits include improved performance and improved ease of manufacturing.

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Method for a surface-mounted LGA socket contact

Disclosed is a method for a surface-mounted land grid array (LGA) socket contact. Benefits include improved performance and improved ease of manufacturing.

Background

              One way to surface mount the LGA contacts is to use a solder-ball type of connection. Conventional LGA contacts utilize a type of design termed double compression. Both interfaces of the contact are put in compression to make an electrical connection from the contact to the package and circuit board interfaces.

              Contact resistance of double-compression LGA contacts can be large due to the small contact area on both interfaces. Eliminating the small surface area of one of the interfaces by using a surface-mount feature, such as a solder ball, lowers the overall contact resistance for the contact, improving the electrical performance of the contact. Alignment pins for double compression sockets are required to align the pads to the contacts (see Figure 1).

              Large contact forces to compress an LGA package is typically accomplished by physically sandwiching the package and circuit board together using a bolted or screwed assembly. Large stiffening plates keep the devices flat.

              Motherboards are conventionally masked for special Au placement for the double compression pads. They require some type of alignment to the motherboard, which impacts routing because it must circumvent the extra holes.

              Interface resistance has limited the amount of current a contact can carry. Typically, more contacts are added to deliver the required current to the package.

General description

              The disclosed method is a surface mounted, single compression contact for connecting an LGA electronic package and a circuit board with a reflow-style attachment. It lowers the cost of the circuit board by eliminating the expensive plating on the circuit board pads and the masking process that is required only to plate the socket pads.

              By surface mounting the contact to one of the interfaces (circuit board or package), the force required to make a consistent electrical connection is reduced by half. Another benefit is that the interface electrical resistance is reduced due to the larger surface area of contact. The contact also helps with the alignment of the socket to the circuit board by not requiring alignment pins for the socket due to being attached to the board.

              The key elements of the method include:

•             Surface mounted, single compression conta...