Despite the fundamental advantages of high density packaging, the introduction of advanced technology has been very slow. One of the difficulties has been the unreliability of low-force pressure contacts which has hampered exhaustive testing of chips prior to mounting and has restricted our choice of high-density, reversible mounting technologies (such as the original active substrate configuration).
To attack this problem, we designed, built, and carried out preliminary experiments with a novel instrument that is essentially a combined scanning tunneling microscope and atomic force microscope (STAFM). This allowed us to measure the electrical properties of contacts with controllable forces down to a few , many orders of magnitude below those normally employed. In this way, we can not only study low-force contacts per se, but can build up a model of macroscopic contacts as arrays of STM's in parallel.
In the preliminary experiments carried out under this contract, we were able to demonstrate electrical conduction between gold surfaces quite close to the value predicted by the deformation of a gold surface under the action of the tip. This apparatus was the subject of a paper presented at the Holm conference on contacts in 1992. Because this work was judged to have medium-to-short term applicability, the project was picked up by the SRC in 1991.