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Printed Circuit Board Wire and Device Add Process

IP.com Disclosure Number: IPCOM000114937D
Original Publication Date: 1995-Feb-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 104K

Publishing Venue

IBM

Related People

Boyko, CM: AUTHOR [+6]

Abstract

Existing thermal carriers have limited wireability, require tradeoffs between thermal resistance and dielectric strength performance, and they may also require costly machining operations to optimize the thermal performance. These carriers generally consist of a thick copper (2 oz. or greater) signal layer on one side of a dielectric layer, and a heatsink layer on the opposite side of the dielectric. The dielectric layer may be thermally enhanced to assist in heat transfer from the signal layer to the heatsink. Limited wireability is a function of the single, heavy copper signal layer. As system dielectric breakdown requirements increase to higher levels (i.e., greater than 2000 Volts), the solution is to increase the dielectric thickness. This in turn ends up degrading the thermal performance of the carrier.

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Printed Circuit Board Wire and Device Add Process

      Existing thermal carriers have limited wireability, require
tradeoffs between thermal resistance and dielectric strength
performance, and they may also require costly machining operations to
optimize the thermal performance.  These carriers generally consist
of a thick copper (2 oz.  or greater) signal layer on one side of a
dielectric layer, and a heatsink layer on the opposite side of the
dielectric.  The dielectric layer may be thermally enhanced to assist
in heat transfer from the signal layer to the heatsink.  Limited
wireability is a function of the single, heavy copper signal layer.
As system dielectric breakdown requirements increase to higher levels
(i.e., greater than 2000 Volts), the solution is to increase the
dielectric thickness.  This in turn ends up degrading the thermal
performance of the carrier.  Finally, a partial solution to the poor
thermal performance of the thicker dielectrics is to grind, laser
ablate, or otherwise mechanically remove selected areas of the
dielectric material such that high power dissipating components may
be bonded directly to the heatsink.  Since the heatsink layer also
serves as a ground plane, direct bonding of components is only
applicable to those components whose bonding area is at ground
potential.

      It would be desirable to have a low cost, yet high wireability
thermal carrier that is capable of withstanding voltage biases
greater than 2000 volts while also providing thermal resistances less
than 1ºC per watt.  The ideal carrier would contain multiple
signal wiring layers, and also provide for direct bonding of high
power dissipating components to a heatsink.

      The thermal carrier design and process described below and
shown in the Figure provides a method to achieve the desired
properties described above.  The basis of the enhanced thermal
carrier is the use of a thin, thermally enhanced Polymer Thick Film
(PTF) dielectric material (i.e., EMCA P-7134-A1203 filled) or a
photoimageable solder mask material (i.e., IBM ASMS) as a dielectric
layer between signal layers and between signal and power or ground
layers.
  1.  A thick (0.020"-0.080") metal plate serves as the substrate/
       carrier, as well as a heatsink and ground plane.  This metal
       plate may be copper, copper plated aluminum,
copper-invar-copper,
       aluminum, molybdenum-copper, etc.
  2.  The dielectric material described above is screen printed or
       coated by other conventional means on the top side of the
metal
       plate.  Either pattern screen printing for P...