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Same Process Defined LGA Pad and Socket Locating Features Disclosure Number: IPCOM000240426D
Publication Date: 2015-Jan-29
Document File: 1 page(s) / 24K

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Disclosed is a process to accurately align substrate pads with socket contacts in a Land Grid Array (LGA).

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Same Process Defined LGA Pad and Socket Locating Features

Locating features for Land Grid Array (LGA) socketing includes the use of pins in sockets and holes in substrates, as well as cutouts in substrates used for corner alignment. In all cases, the substrate alignment features are formed by a process independent of the features to be aligned, that is the LGA pads. Tolerances for these additional processes must be considered in design.

To enable fine pitch LGA interconnect, it is necessary to reduce positional tolerances between the socket and substrate contacts. The elimination of independent processes in forming substrate-locating features improves positional tolerance.

Positioning of substrate contacts to substrate locating features is formed by the same process, typically a photo imaging process. A copper (Cu) pad is formed for solder attachment of an alignment feature, typically a copper ball, using the same process and process step as that which forms the copper pads for the electrical interconnect features. The copper ball self-aligns on solder reflow due to surface tension, minimizing the tolerance accumulation between the electrical contacts and locating features on the substrate.

A copper pad for a substrate-locating feature is formed on the substrate bottom at the same time as pads for electrical contacts are formed. A copper ball or other shape is soldered to this copper pad in such a manner as to permit self-centering due to surface tension. An app...