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DYE INDICATORS FOR VISUAL DETECTION OF ORGANIC PROTECTIVE COATINGS ON PRINTED CIRCUIT BOARDS

IP.com Disclosure Number: IPCOM000007309D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2002-Mar-13
Document File: 4 page(s) / 211K

Publishing Venue

Motorola

Related People

Melanie Williams: AUTHOR [+3]

Abstract

A method of detecting organic inhibitor coat- ings (Entek, Protecto, Schercoat) on printed circuit boards was developed to allow visual inspection and identification of defects on incoming boards. Visual detection is accomplished by incorporating select organ& dyes into the organic inhibitor solution prior to coating deposition such that a colored coating is produced. The criteria for dye selection was estab- lished by evaluating various classes of dyes. Solubil- ity in the inhibitor solution and non-reactivity with the metal ions present in the inhibitor solution were found to be critical requirements for dye selection.

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MOTOROLA Technical Developments Volume 23 October 1994

DYE INDICATORS FOR VISUAL DETECTION OF ORGANIC PROTECTIVE COATINGS ON PRINTED CIRCUIT BOARDS

by Melanie Williams, Faye Nounou and Tom Swirbel

rating an organic dye into the protective coating prior to the application procedure. This process allowed a set of criteria to be established for evaluating dyes as additives to organic protective coatings solutions. This report describes the results of coating detec- tion after dye incorporation and the criteria estab- lished for dye selection.

ABSTRACT

  A method of detecting organic inhibitor coat- ings (Entek, Protecto, Schercoat) on printed circuit boards was developed to allow visual inspection and identification of defects on incoming boards. Visual detection is accomplished by incorporating select organ& dyes into the organic inhibitor solution prior to coating deposition such that a colored coating is produced. The criteria for dye selection was estab- lished by evaluating various classes of dyes. Solubil- ity in the inhibitor solution and non-reactivity with the metal ions present in the inhibitor solution were found to be critical requirements for dye selection.

EXPERIMENTAL:

  A variety of colored dyes were evaluated for incor- poration into a typical commercial organic protec- tive coating formulation. The dyes evaluated included fluorescein; water soluble fluorescein; 2:7"-dichloro- fluorescein; 4,5-dihydroxynaphthalene-2,7-disulfonic acid, disodium salt dihydrate; Alizarin Red S mono- hydrate; Bromocresol Purple; Crystal Violet; Methy- lene Blue; Basic Blue 3; and Basic Red #29. The structure ofthese dyes are shown in Figure 1.

  The dye-containing formulations were prepared by adding a dye directly to a commercial inhibitor coating solution (Entek Cul06A") at 40 C, stirring for one minute and allowing the solution to stand for 15 minutes. The solutions were then evaluated for dye dispersion, solubility, and the absence of com- plex formation. Formulations which met the requi- site criteria were coated on printed circuit board lam- inates to evaluate coating adhesion, coverage, and surface selectivity (coverage on copper versus non- metallized regions and coverage on clean versus oxi- dized copper). Varying concentrations of the dye, ranging from O.Ol%-5.0%, were tested to select the optimum concentration for visual detection. Test boards were prepared by immersing printed circuit boards in stirred inhibitor solutions containing the dye for one to two minutes after processing boards through the manufacturers recommended cleaning and etching steps.

INTRODUCTION:

  Organic inhibitor coatings (for example, Entek Cul06A," ProtectoF and Schercoat") are becoming widely used as protective coatings to prevent oxi- dation and corrosion of the bare copper surfaces on printed circuit board assemblies. These coatings have become accepted as viable Hot Air Solder Leveling (HASL) replacements for PCB assembly technologies requiring surface pla...