Browse Prior Art Database

Electronic Card Conformal Coating for use with Surface Mount Technology and Water Based Solder Paste

IP.com Disclosure Number: IPCOM000106705D
Original Publication Date: 1993-Dec-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Rose Jr, FM: AUTHOR

Abstract

Circuit boards are often adversely affected by moisture both before and after population, resulting in card delamination or metal migration between lands. A protective conformal coating can prevent absorption of water but usually results in an added step to remove the coating prior to screening of solder paste. If the card is to be protected after population, the coating must be re-applied.

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Electronic Card Conformal Coating for use with Surface Mount Technology and Water Based Solder Paste

      Circuit boards are often adversely affected by moisture both
before and after population, resulting in card delamination or metal
migration between lands.  A protective conformal coating can prevent
absorption of water but usually results in an added step to remove
the coating prior to screening of solder paste.  If the card is to be
protected after population, the coating must be re-applied.

      When water soluble flux is used in the solder paste, a unique,
permanent conformal coating can be produced from Fluorad FC-725*.
This material can be thinned with various solvents and sprayed,
dipped, or brushed on the freshly manufactured card to produce the
desired coating.  The shelf life of the raw card is increased because
the coating prevents moisture absorption.

      Solder paste with both solvent soluble and water soluble fluxes
can be screened directly onto this coating without an extra removal
step.  When a solvent based flux is used, the coating is removed in
the flux cleaning step.  With water based flux, however, the coating
remains intact throughout placement, reflow, and flux removal.  The
populated card is still protected from moisture.

      The choice of thinning solvent for Fluorad FC-725 may be
tailored to the paste to be used.  A 1:1 mixture of n-butyl acetate
and Fluorad works well for solvent based fluxes.  A more polar
solv...