Compressible Connectors For 3D Stacked Modules

I have had the privileged to work on some very interesting technology related to solderless, compressible connectors[1]. I know, compressible connectors don’t sound very exciting. While that may be true now, at the time they were exciting to be working on since they were critical for achieving low cost, very compact transmit/receive (T/R) modules for phased array radar.

One of the goals of my investigation, besides being compressible, was for the connector to be compatible with very high volume production. I settled on the investigation of elastomeric and fuzz button connectors because they were being used in applications such as hard disk drives and microwave ovens. However, they had never been applied to applications above a few MHz. The innovation, for which I was awarded 2 patents (patent numbers 5,675,302 and 5,552,752), was that I developed a method to use those connectors at X-Band frequencies (7-11GHz) which was about a 1000 times increase in the electrical bandwidth.

A key to developing these connectors was the use of commercially available 3D finite element modeling software. At that time, this type of software was new and it was not clear that it would be useful in practical circuit/system designs. It seems funny to say that now, as this type of software is ubiquitous and a critical part of many design processes. I quickly became one of the mega power users (top 1%) of this type of software.

I developed compressible connectors using elastomerics and fuzz buttons. The former turned out to be of minor practical use due to the fact that elastomeric connectors could loose contact due to recession of the metal contacts into the elastomer. However, the fuzz button was very useful and I designed it into 3D modules for phased array radar. Figure 1 shows a graphic from one of the patents I was awarded for the compressible connectors.

Basically, the connectors allow two substrates (containing electronics) to make electrical contact to transfer electrical signals vertically from one layer to the next. This allows multiple substrates to be stacked to form a 3D module. The result is a module that is extremely compact.

Figure 1. Illustration from one of my patents showing how the compressible connectors are used.

[1] R. Sturdivant, et. al., “Using the Matrix Metal-On-Elastomer Connector at Microwave Frequencies,” ISHM 94 Proceedings. pp340-344.

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