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Encapsulated Dendrite Electrical Interconnect for Surface Mount Applications

IP.com Disclosure Number: IPCOM000116177D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Arrowsmith, P: AUTHOR [+2]

Abstract

A method for attaching Surface Mount Technology (SMT) components to a printed circuit card (PCB). The electrical interconnect is provided by metallic dendrites on the PCB pad surfaces which penetrate into a compliant conductive coating on the component leads when the component is placed and pushed down. The strength and reliability of the attachment is provided by an electrically insulating encapsulant that is UV and/or thermally cured. The encapsulant may be dispensed on the PCB before the components are placed and the assembly can be tested and faulty components replaced prior to cure.

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Encapsulated Dendrite Electrical Interconnect for Surface Mount Applications

      A method for attaching Surface Mount Technology (SMT)
components to a printed circuit card (PCB).  The electrical
interconnect is provided by metallic dendrites on the PCB pad
surfaces which penetrate into a compliant conductive coating on the
component leads when the component is placed and pushed down.  The
strength and reliability of the attachment is provided by an
electrically insulating encapsulant that is UV and/or thermally
cured.  The encapsulant may be dispensed on the PCB before the
components are placed and the assembly can be tested and faulty
components replaced prior to cure.

      It has been previously demonstrated (*) that reliable physical
interconnects can be made when one or both of the metal contact
surfaces are coated with small, sharp aspherities or dendrites.
Typical dendrite dimensions are 5-10 &mu.m diameter and 20-35 &mu.m
length.  The dendrite connection is formed by pushing the two
surfaces together and maintaining a force of >=30 gm.  Low electrical
resistance (~1 m&Omega.) is obtained, even in the presence of
dust and dirt, because the dendrites penetrate any oxide film or
contamination.  Dendrite connections can be made and unmade, as long
as the dendrites are not broken off.  Dendrites have been previously
used to make demountable, temporary pad-to-pad connections for chip
testing and burn-in and for flex-to-rigid connections.

      The subject of this disclosure is the application of dendrite
interconnects to general SMT assembly with most types of industry
standard component.  The Figure shows a schematic of a cross-section
through the dendrite connections for a typical SMT component.
Palladium dendrites (for example) are plated on the copper pads of
the PCB card.  The leads of SMT components are typically coated with
~25 &mu.m of lead-tin solder which is conformal and readily
deformed, allowing the dendrites to penetrate and make an
interconnect w...