Browse Prior Art Database

Improved Developer Composition for Soldermasks

IP.com Disclosure Number: IPCOM000102527D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Crocket, C: AUTHOR [+5]

Abstract

The disclosed developer solution has a lower chemical activity than the solution currently used for developing epoxy-based photoimagable soldermasks. By using a less aggressive developer solution, the defects due to voids and undercutting may be reduced.

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Improved Developer Composition for Soldermasks

       The disclosed developer solution has a lower chemical
activity than the solution currently used for developing epoxy-based
photoimagable soldermasks.  By using a less aggressive developer
solution, the defects due to voids and undercutting may be reduced.

      The image quality and integrity of a photoimagable soldermask
is highly dependent on the develop step.  Where a spray developer is
employed, this is a combination of physical/mechanical properties
(spray pressure, nozzle configuration, temperature) and the chemical
properties of the solvent system used.  Typically, a solvent system
is chosen that is a marginal solvent for the polymer system being
developed [*] so that the mechanical actions override the chemical
actions of the developer.  This minimizes the potential for swelling
and overdeveloping the resist (due to solvent penetration into the
polymerized resist) while still allowing the through holes in the
circuit board to be cleaned out.

      In the case of Probimer 52*, the solvent recommended as a
developer, gamma-butyrolactone (g-BLO), is very chemically active and
is an excellent solvent for that and other epoxy-based soldermasks.
This dictates a narrow process window for develop, where
underdeveloping leads to coating in the holes and on tabs and
overdeveloping increases undercutting of the resist and causes voids.
Typically, the develop step is controlled by residence time, spray
pressure, and temperature.

      If a less aggressive solvent were used, a wider process
latitude could be realized wherein the spray pressure and/or the
residence time could be increased to provide enough physical action
to clear the holes and tabs, yet the lower chemical activity would
reduce the tendency to undercut the resist and cause voids.

      For this study, water was evaluated as an additive to g-BLO.
Water is not flammable or toxic, is not a good solvent for epoxies
and is miscible with g-BLO in all proportions.  The solubility of
Probimer 52 in various water/g-BLO mixtures was evaluated.  In ratios
up to 11:89 water:g-BLO, Probimer 52 is soluble in excess of 200 g/L.
At higher water content, the solubility decreased rapidly, and at
water contents greater than 13:87 water:...