Copper Deposit
Galvanic metal buildup inside plated through holes represents knee copper plating during multilayer circuit board fabrication. Excess thickness along barrel entry regions creates mechanical stress gradients that cause barrel cracking during thermal shock exposure. Etching rates vary across board cross sections and thin barrel centers demand higher throw power chemistry to prevent microvoiding failures.
Microsection metallography reveals copper thickness measurements along barrel walls and verifies plating uniformity between external surfaces and internal interconnects.
Barrel Reliability
Current density distribution dictates metal accumulation rates inside drilled channels during acid copper electrodeposition. High aspect ratio designs restrict electrolyte mass transport and starve central barrel regions of cupric ions unless pulse periodic reversal rectification is applied. Subsequent thermal stress testing through solder float simulation induces mechanical strain on fragile transition zones.
Brittle deposits fracture prematurely under cyclic thermal expansion loads when organic brighteners contaminate the bath chemistry.
Process Verification
Cross sectional analysis verifies plating integrity by measuring deposit thickness at barrel centers versus surface foils. Metallographic preparation requires precise grinding through hole axes to expose the internal copper wall without smearing ductile metal across dielectric layers. Acceptance criteria demand minimum copper thickness values inside the barrel to satisfy IPC standards for high reliability electronics manufacturing.
