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Solving Soldering Hierarchy Problems by Metallurgy And Design

IP.com Disclosure Number: IPCOM000119324D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Gall, TP: AUTHOR [+3]

Abstract

Packaging of semiconductor devices into a module which was soldered to a card, which then had connectors attached, used a hierarchy of solders with the highest melting point solder used for the first operation. Lower melting point solders were used for each subsequent operation so that the joints previously formed would not remelt in the later soldering processes (*). For a complex product involving multichip interposers, surface mount devices pin grid array and edge connectors, and possibly optical cable connectors, the soldering hierarchy approach becomes extremely awkward. There may not be enough different solders with distinct melting points to make a reliable joint for each of the components.

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Solving Soldering Hierarchy Problems by Metallurgy And Design

      Packaging of semiconductor devices into a module which
was soldered to a card, which then had connectors attached, used a
hierarchy of solders with the highest melting point solder used for
the first operation.  Lower melting point solders were used for each
subsequent operation so that the joints previously formed would not
remelt in the later soldering processes (*).  For a complex product
involving multichip interposers, surface mount devices pin grid array
and edge connectors, and possibly optical cable connectors, the
soldering hierarchy approach becomes extremely awkward. There may not
be enough different solders with distinct melting points to make a
reliable joint for each of the components.

      The disclosed method utilizes a layered Pb/Sn structure and the
metallurgical reaction occurring in the joining to accomplish a
number of joining steps with a same peak process temperature.  The
metallurgical reaction raises the melting point of the solder after
the initial low temperature joining so that the solder does not
remelt during the following processes.

      The advantages of the layered Pb/Sn solder are:
1.   The same process is used for all levels of joining, so that a
single process and set of equipment can be used for all levels of
joints instead of several solder processes with different process
temperatures.
2.   The need for very high melting point solder for the first step
is eliminated, so the stress on the product due to cooling from a
high temperature solder process is eliminated, and lower temperature
compatible materials...