Browse Prior Art Database

Capillary Pin Head for "Step" Process

IP.com Disclosure Number: IPCOM000120116D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 3 page(s) / 99K

Publishing Venue

IBM

Related People

Senger, RC: AUTHOR

Abstract

Disclosed is a technique to achieve good solder joints between chip carrier package pin leads and the substrate circuit lands, by placing solder preforms on top of the pin heads which have been formed to allow capillary action to direct the reflowed solder to the interface between the pin head and substrate land (see the figure).

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This is the abbreviated version, containing approximately 52% of the total text.

Capillary Pin Head for "Step" Process

      Disclosed is a technique to achieve good solder joints
between chip carrier package pin leads and the substrate circuit
lands, by placing solder preforms on top of the pin heads which have
been formed to allow capillary action to direct the reflowed solder
to the interface between the pin head and substrate land (see the
figure).

      Standard metallized ceramic (MC) substrates are soldered (both
pin head to land, and C4 (controlled collapse chip connection)
fingers) by a dip tinning (solder) process which immerses the pinned
substrate in flux, and a molten solder bath to deposit the solder.

      Recent efforts have qualified an alternative to this process
for substrates with 100 mil pin grids.  This process which is
referred to as "STEP" (Substrate Tinning Elimination Process)
selectively solders the substrate pin heads to the circuit lands and
does not deposit solder on the pin leads or C4 lands.

      The technique used for STEP is to deposit a small quantity of
flux and a solder ball preform adjacent to the pin head and on the
circuit land, and then pass the part through a high temperature
furnace to achieve reflow of the solder ball which then flows/wets
around the pin head/land interface to form the solder joint.

      Attempts in the past to place the solder ball preform on top of
the pin head to form this joint have been unsuccessful because the
surface tension of the molten solder does not allow the solder to
flow over the edge of the pin head and then down to the land (see
the figure, Section A-A).

      Having to place the solder ball adjacent to the pin heads
results in limiting the density of pins and land circuitry on the
substrate.  Recent analysis of using the STEP process for 50 mil
grids has resulted in the conclusion that it is not achievable with
the present techniques.

      This disclosure describes a technique to overcome the problem
of placing the solder preform on top of the pin head and thereby
achieve 50 mil and smaller grids.

      I...