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Photolithography Definition of Solder Paste

IP.com Disclosure Number: IPCOM000103259D
Original Publication Date: 1990-Sep-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 65K

Publishing Venue

IBM

Related People

Munroe, RA: AUTHOR

Abstract

Disclosed is a method of applying solder paste in readily controlled dimensions and further defining the applied pattern with photolithography. A similar method of applying metal powder in precise patterns using photolithography is the Dupont Corporation's FODEL process. The FODEL process uses solvents.

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Photolithography Definition of Solder Paste

      Disclosed is a method of applying solder paste in readily
controlled dimensions and further defining the applied pattern with
photolithography.  A similar method of applying metal powder in
precise patterns using photolithography is the Dupont Corporation's
FODEL process.  The FODEL process uses solvents.

      A fine solder powder such as 63/37 tin/lead would be mixed with
a water soluble photosensitive binder and polymers to make a solder
paste.  Polymers are used to enhance the screening of the solder
paste.  A flux material is suggested that is either of the no-clean
type, removed by reactive gas reflow, or is water soluble.  One water
soluble photosensitive material is unpolymerized polyvinyl alcohol.

      The solder paste is screened onto a fine pitch pattern on a
substrate in the next step.  One example would be a TAB (Tape
Automated Bonding) device that has many leads (in excess of 100) that
are on 0.5mm pitch or less.  The screener used would be the same as
is used today to apply solder paste.  The deposited pattern would be
applied approximately in the area and it is suggested that the
pattern be a solid pattern that covers all circuit pads on the
substrate.

      The next step is to expose the solder paste deposit to a light
source through a mask or film that is registered to the exact pattern
desired.  One method is a non-contact mask with a collimated UV
(UltraViolet) light source. ...