Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!samsung!caen!spool.mu.edu!agate!bionet!parc!minsky
From: minsky@parc.xerox.com (Henry Minsky)
Newsgroups: comp.arch
Subject: Re: Faster busses are hard; can we do wider?
Message-ID: <1991Jun21.195509.28579@parc.xerox.com>
Date: 21 Jun 91 19:55:09 GMT
References: <1940@array.UUCP>
Sender: news@parc.xerox.com
Organization: Xerox PARC
Lines: 51

In article <1940@array.UUCP> colin@array.UUCP (Colin Plumb) writes:
>
>Cinch Coinnectors make a tangled-wire-bump called the Synapse that has
>gorgeous electrical properties (.5 nH per pin) and they pack on 40 mil
>centres, about 1 mm.  100 connectors per square cm makes massively
>wide data buses feasable.
>
>Would anyone like to share experiences, opinons, or prejudices?
>-- 
>	-Colin

We are designing a multiprocessor using packaging based on the Cinch
technology; We had them injection mold custom connectors which are
square arrays about an 1.4 inches square, with an array of 372 20 mil
buttons (fuzzballs) of 1 mil gold-copper alloy wires stuffed through
holes in the connector, and sticking out each side. We package our
network chips in custom packages which we call pad-grid arrays (or
Land Grid Arrays). The chip carriers have pads on both top and bottom
of the package, and thus we can use the Cinch Connectors to connect
the chip to both the PC board below it, and the PC board above.

The Cinch connector, and our chip carrier have enough extra feed
throughs that we can use the packaging as both the chip-to-board
connections, and the board-to-board connections. This lets us dispense
with the backplane entirely; all signal flow between boards is very
short wire length, and can have good impedance matching. 

The connectors have channels molded in for liquid cooling
(fluorinert). The chip carriers also also have channels and an
integral heat-sink for running the fluid across the back of the chip.


The fuzzbutton connectors are very low resistance, unlike some of the
conductive polymer or wires-in-silicone sheets. We believe that the PC
Board traces can be impedance matched with the connectors, although we
haven't really done enough experiments with this yet. 

There is one problem with the connectors; the fuzz buttons have an
amazing affinity for human fingertips; the little wire balls tend to
grab onto the whorls on your fingertips, and get pulled out of their
holes. This means you need to be careful when handling the connectors.
Otherwise, the connectors seem quite reliable; we have encased a
sample board in plastic and then sanded it away to get a
cross-section, and the buttons make very good compression area contact
with the pads of the board and chip-carrier. And the whole system is
solderless, giving easy access for debugging our prototypes. 

The entire stack of boards and chips will be held under compression
using two cast aluminum tooling plates, with through bolts to squeeze
the stack. The cooling fluid can be pumped through manifold channels
machined into the aluminum endplates.