Browse Prior Art Database

Dynamic Method for Enhanced Electrical Connection

IP.com Disclosure Number: IPCOM000118740D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 155K

Publishing Venue

IBM

Related People

Alcoe, DJ: AUTHOR

Abstract

Disclosed is a method for encouraging contact and wetting of a quantity of molten solder to a nearby feature, such as an electrical contact pad. At least one resonant mode of the quantity of molten solder is excited with vibrational input to create dynamic movement of the solder and, therefore, promote contact and wetting. A device floating on several molten quantities of solder may also be resonated to promote contact between the device and additional quantities of molten solder. The dynamic method allows solder reflow to successfully occur in the face of some non-flatness of a device and/or variations in the volumes/sizes of the several quantities of molten solder.

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This is the abbreviated version, containing approximately 35% of the total text.

Dynamic Method for Enhanced Electrical Connection

      Disclosed is a method for encouraging contact and wetting of a
quantity of molten solder to a nearby feature, such as an electrical
contact pad.  At least one resonant mode of the quantity of molten
solder is excited with vibrational input to create dynamic movement
of the solder and, therefore, promote contact and wetting.  A device
floating on several molten quantities of solder may also be resonated
to promote contact between the device and additional quantities of
molten solder.  The dynamic method allows solder reflow to
successfully occur in the face of some non-flatness of a device
and/or variations in the volumes/sizes of the several quantities of
molten solder.

      The disclosed method pertains to the problem of solder reflow
of ball grid array modules, controlled collapse chip connection (C4),
solder paste reflow, etc., to form a solder connection between some
electrical device and a corresponding circuitized substrate.  The
specific problem addressed is that of forming said connection despite
non-flatness of the device, substrate, or both.  The problem is
realized when "non-wets" occur, i.e., a few of the many solder balls
fail to touch and wet to connection pad resulting in electrical open
circuit defect.  Known means of correcting such a result include
increasing quantity of solder used to form connection.  However, if
too much solder is used, "bridging" can occur between nearby
connections, resulting in an electrical short circuit defect.

      As device sizes become larger, this problem becomes aggravated;
use of finer pitch connections on devices also reduces the quantity
of solder which can be used to form a connection.  Obtaining a nearly
flat device for connection is a particular challenge for plastic and
organic chip packages, due to flexibility of the package and
temperature-related processing requirements.  Therefore, a method
which can help to avoid chip or ball non-wets despite non-flatness
would be of great value to the electronics industry.

      Disclosed is an enhancement of known C4 and Ball Grid Array
(BGA) attach methods.  It is compatible with the known methods of
reflowing homogeneous solder balls (typically eutetic, "low-melt"),
reflowing enhanced-standoff BGA (combination of low-melt and
high-melt solder), or reflowing solder-coated ball structures.  Use
of solder paste  is also compatible.  The method can be used if the
device is a chip or  if the device is any kind of BGA (plastic,
organic, metal, ceramic) with  which reflowed solder is used to form
electrical connections to a circuitized substrate and the device is
made to "float" on the reflowed  solder.

      The method may be implemented by acoustically resonating the
device while the solder is molten, so that the vibrational movement
of the device encourages wetting and solder contact, despite
non-flatness of the attachment site and/or the device.  Vibr...