1. Field of the Invention
This invention relates generally to using a wave spring to clamp an IC component to a substrate, and more specifically relates to using a wave spring to clamp a land grid array (LGA) IC component to a printed circuit board.
2. Description of the Prior Art
In many data processing systems (e.g., computer systems, programmable electronic systems, telecommunication switching systems, control systems, and so forth) very large pin count electrical components (e.g., application specific integrated circuits and processor chips) are assembled on substrates (e.g., printed circuit boards, other flexible substrates, multi-chip modules, and equivalents). One type of packaging that is frequently used for a very large pin count electrical component is what is commonly known as a land grid array (LGA) component. Electrical connections between the LGA component pins and the corresponding conductive pads on the substrate are typically achieved by compressing an interposer (e.g., an elastomeric conductive material) containing several perpendicular conductive channels (e.g., buttons or columns filled with conductive balls or conductive threads).
In order to achieve reliable electrical connection between the LGA pins and the conductive pads of the substrate, such LGA components are clamped by screws and springs to the substrate with high perpendicular clamping forces (exceeding several hundred pounds or several hundred newtons of force). However, achieving such large perpendicular forces with conventional springs requires either the use of long springs (and screws) that vertically project above the substrate, or the use of shorter springs with very large spring constants.
One problem with using long springs (and screws) is that the vertical projection above the plane of the substrate seriously limits the packaging density of adjacent parallel substrates in order to avoid contact to an adjacent substrate by the springs and screws of another substrate. A problem with using shorter springs with very large spring constants is that the clamping force is determined by the mechanical tolerances in compressing the springs, but there is a significant manufacturing deviation (e.g., +/xe2x88x9210% in the spring constant from one spring to another spring in the same manufactured lot. Therefore, if two springs with very large spring constants are mechanically compressed by an equal distance, the resulting forces applied by the two springs can be greatly unequal, causing uneven clamping and uneven electrical contacts to the interposer and the conductive pads of the substrate under the LGA component. Uneven electrical contacts in turn can cause poor electrical contacts that produce a permanent or an intermittent failure in system operation. Another problem with short, conventional springs is that the springs are compressed near or to a coil-bound or solid height condition outside of their usable range.
Since the pin counts for IC components are continually increasing, the necessary clamping forces for LGA components and the necessary spring forces will increase. Without improved springs to apply the clamping force, very long springs will be needed, or short springs with high spring constants and large force variations will produce an increasing number of poor electrical contacts between LGA components, interposers, and substrates, resulting in increasing operational and reliability failures.
It would be desirable to use a relatively shorter spring with a smaller spring constant that can supply the necessary spring force to clamp a component to a substrate.
The present invention uses a relatively shorter spring with a smaller spring constant that can supply the necessary spring force to clamp a component to a substrate.
A first aspect of the invention is directed to a method to use a wave spring to lamp a component to a substrate having a first side and a second side. The method includes placing the component on the first side of the substrate; placing a structure on the component, wherein the structure has a plurality of holes; placing a plurality of wave springs on a plurality of bolts; inserting the plurality of bolts into the plurality of holes of the structure; and attaching the plurality of bolts to the substrate.
A second aspect of the invention is directed to an assembled substrate. The assembled substrate includes a substrate having a first and a second side, and an electrical contact area on the first side; an interposer placed on the electrical contact area; a component placed on the interposer; a block having a plurality of holes placed on the component; a plurality of bolts and a plurality of wave springs inserted in the plurality of holes, wherein the plurality of bolts and wave springs clamp the component, the interposer and the substrate together on the electrical contact area of the substrate.
These and other objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.