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MO-LA INC. Technical Developments Volume 18 March 1993
SOLID DYE PENETRANT FOR CRACK Dl3ECTION
by Shailesh Mulgaonker
DYE PENElRAllON IN PLASTIC SEMICONDUCTOR
PACKAGES
The current technique of ascertaining microcracks in packages comprises of penetrating dye into the pack- age. The dye is typically fluorescent under UV light. The package is decapped, typically by grinding, mechanic- ally removing or milling off the top or bottom half of the package. The dye traces identify the extent and location of the cracks.
DISADVANTAGES IN THE TECHNIQUE
The decapping operation itself introduces artifacts, such as crack propagation and creates new cracks. The operation of grinding often leads to smearing of the dye in areas originally devoid of cracks prior to decapping. The use of a dye penetrant that solidifies at room tem- perature, or at slight elevations of temperature after pen- etration into the cracks, would eliminate errors in inter- pretation, since the solid&d dye would not ingress further during the mechanically stress-intensive decapping operation.
THE FORMULATION FOR THE SOLID DYE
The fluorescent dye (sold commemially by MagoatIux Carp, USA-tradename Zyglo, or Eishin Chemical Com- pany, Japan- tradename F-4A-E) typically comprises of ParatXnic and Aromatic Hydrocarbons (e.g. white min- eral oil, kerosene), non-ionic surface active agents, plas- ticizer and fluorescent salt (e.g. fluorescein). The salt serves to track the defect, the non-ionic surface active agents serve as wetting agents, the plasticizer serves to modify fluid flow properties, and the hydrocarbons serve as solvents. This formulation needs to be mixed with a polymeric material which allows the solution of the dye, as well as polymerizes after penetration, thus entrapping the dye in the matrix formed. Considering the dye chem- istry, acrylates serve as good emulsifiers and solvents, creating a homogeneous phase with the dye while simultaneously maintaining the penetrant ability. The acrylate resin chosen comprises of polyhydroxy substi-
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tuted bisphenol A dimethacrylate resin, benzoyl perox- ide (commercially sold by Polysciences, USA as LR White) with the accelerat$r comprised of polyethylene glycol and N,N-diiethyl-p-toluidine. In the above, the methacrylate is the monomer, the peroxide is the redox initiator of the polymeri&+, while the accelerator serves to accelerate the polymerization kinetics. Also, acrylates are used extensively as specimen mounts, with this spe- cific resin chosen due to its penetrant abiity based on inliltration into living t&u+ while preserving tissue mor- phology. Moreover, the resin is hydrophilic in nature, thereby readily emulsifying the dye, rendering the sys- tems compatible. Besides, the resin polymerizes anaerobically.
METHODOLOGY FOR THE SOLID DYE
PENETRANT INSPECTlON
The method described herein involves penetrating the part with the formulation comprised of well-mixed Resin (65 parts by wt.), Hardner (3 parts by wt.), and the...
