Contact Failure
Interface failures between a copper microvia and its corresponding lower trace pad disrupt the internal signal routing of high-density interconnect circuit boards. Microvia target pad separation arises when the deposited copper tube breaks its connection with the pad beneath it. This issue differs from barrel cracking by occurring specifically at the flat interface where the via bottom sits on the next layer.
Thermal Stress
Differences in coefficient of thermal expansion between the epoxy resin substrate and the copper cylinder generate high tensile stresses at this junction. When the board heats up during soldering, the epoxy expands vertically much faster than the copper via barrel. This expansion exerts an upward pull that breaks any weak chemical or mechanical bond at the pad interface.
Reliability Impact
Intermittent connections resulting from this separation can pass initial board-level electrical tests but fail in the field. These failures often return as intermittent noise or system crashes that occur only when the product reaches its operating temperature. Applying strict desmear and copper activation processes before plating is the primary method used to ensure a strong, reliable bond at the target pad.
Fabricators perform highly accelerated thermal cycling tests on test coupons representing the production panels to guarantee that the plated interfaces can withstand the heat of multiple reflow runs without separating.
