Iso Die Package Selection for Compact Surface Mount Assembly
Matching package creepage distance to board pollution degree prevents arc flash failure while maintaining high density surface mount assembly yields.
Ionic Contamination
Chemical Purity
Analytical assessment of circuit board surfaces measures the residue of manufacturing chemicals left behind after assembly processes. High levels of ionic contamination on a printed circuit board lead to electrochemical migration and dendrite growth when exposed to voltage and moisture. This residue originates primarily from flux activators, plating chemistries, and cleaning solvents.
Eliminating these residues prevents long-term circuit failure.
Extraction Method
Sensing systems measure the resistivity of solvent extract to determine the concentration of ionic species present on the sample. The board is immersed in a mixture of isopropyl alcohol and deionized water, which dissolves the surface contaminants. Changes in the conductivity of the solvent are recorded continuously.
The tester compares these readings to a reference standard of known sodium chloride concentration.
Performance Risk
Contaminants deposited on the dielectric surface act as electrolytes, lowering the insulation resistance between adjacent conductive traces. When electricity is applied, the dissolved ions migrate toward oppositely charged conductors, forming metallic paths. These dendritic structures create low-resistance short circuits that can disrupt signal integrity.
The degradation remains hidden until high humidity triggers dendritic growth.
Standard Threshold
Industrial manufacturing specifications establish acceptable cleanliness limits, typically expressed in micrograms of sodium chloride equivalent per square centimeter. For military and high-reliability aerospace hardware, the permissible threshold is much lower than for commercial consumer electronics. Calibration using a high-precision chemical standard verifies the measurement accuracy of the extraction system.
This check is essential for certifying that boards meet quality baselines before they undergo protective conformal coating, ensuring that the coating does not trap active salts against the copper pads.