Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
1999-05-12
2001-09-11
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S730000, C361S748000
Reexamination Certificate
active
06288909
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to double-sided modules for electronic applications, and more particularly to feed through interconnects for such applications.
BACKGROUND ART
In the past, for electronic packaging, it was common to form a housing having internal integral panels with electronic substrates attached to both sides of the panels. In order to route connections between the two substrates, it was necessary to fire-in glass feed throughs. The glass feed throughs required that glass beads having through openings therein would have metal pins inserted in the glass beads. Openings for the route connections would be machined into the panels, the glass beads with the pins would be placed and held in the panel openings, and the entire housing fired in an oven to melt the glass to hold the pins in their proper positions. The housing is then gold plated (including the pins). The substrates would then be secured to both sides of the panel and wires, generally of gold, would be bonded to the substrates and then to the ends of the pins to complete the double-sided module. Another option is a soldered-in feed through.
The above technique had many problems. Sometimes, during the oven firing and cooling process, the glass would develop cracks, chips, holes, or bubbles, which would mean the entire housing would have to be rejected. Even one such flaw would be the basis for rejecting the entire housing. Other times, the glass would climb or melt out of the opening in the panel and solidify on the panel surface. This would prevent the substrate from sitting flat on the panel. By not sitting flat on the panel, the substrate could potentially fail electronically or be destroyed from the mechanical stress of acceleration testing, so housings would be rejected for this reason.
Further, the pin could float from one side to the other during the firing process and move so far off center or be angled such that the substrates could be short-circuited together. Even further, since each feed through had four connection points, two to the substrates and two to the pin, these added additional areas of potential failure.
Also, the pins could be improperly plated, which would be another basis for rejecting the housing. The firing temperature for the glass is above the melting point of the gold. This means the pins must be individually wire-wrapped and electro-chemically gold plated after assembly and firing in an extremely labor intensive process.
In addition, on the design side, the fired-in glass feed through created a limitation on the packing density of the number of feed throughs possible within a given panel space. This is because a certain minimum diameter opening is required to fit in the pin and glass bead combination.
Finally, manufacturing was very costly because special graphite fixtures were required due to the high temperatures of firing and because a great deal of manual assembly was required.
Although rejecting a housing was expensive, no defects could be tolerated because of the critical applications in which the double-sided modules were used. While other alternatives were sought, as the use of metal pins for feed throughs has been an industry standard for over twenty years because no better approach has previously been discovered.
DISCLOSURE OF THE INVENTION
The present invention provides a double-sided module having electrical substrates on either side of a housing panel which are interconnected by a wire connection from one substrate to a conductor-filled through-channel, or via, in the other substrate. The distances from the bonding point on one substrate to the bond vias have to have predetermined ratios of heights to center-to-center distances based on manufacturing techniques and tolerances, and to avoid failure during acceleration testing. A ratio of under 20 to 1 is required to avoid failure under 5,000 gravities of acceleration for a 0.0008 inch diameter wire and under 8.3 to 1 for a 0.002 inch diameter wire. The 5,000 gravities constant acceleration test is an industry standard screen method for electronic modules. The purpose of the test is to identify workmanship defects.
The present invention further provides a feed through which does not require the use of glass, which is subject to cracks, chip-outs, holes, or bubbles.
The present invention further provides a double-sided module which is not subject to glass climb or flow or for potential shorting of the backsides of the substrates.
The present invention further provides for a reduced number of wire bonds to reduce the number of failure modes.
The present invention further provides increased packing density of feed throughs through the housing panel.
The present invention further provides for the elimination of gold-plated pins which may be subject to plating problems.
The present invention further provides an easily automated feed through.
The present invention further provides simple conductive via feed throughs which do not require glass beads, pins, plating of the pins, and double wire bonds.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5728248 (1998-03-01), Weber
patent: 6110823 (2000-08-01), Eldridge et al.
Kelley Brett Armstrong
Richardson Eric Franklyn
Verdon David Andrew
Gaffin Jeffrey
Ishimaru Mikio
Stellex Microwave Systems, Inc.
Tran Thanh Y.
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