Question 1

What is the Dimensional Inflation of Thermal Expansion?

Accepted Answer

Volumetric and linear expansion of electronic packaging materials under thermal load describes the physical behavior of a substrate during solder assembly. This dimensional change, termed thermal expansion, is quantified by the coefficient of thermal expansion, which measures parts-per-million movement per degree Celsius. It behaves anisotropically in woven fiberglass laminates because the stiff glass fibers constrain movement along the horizontal plane while allowing greater expansion in the vertical direction.

Question 2

What is the Material Mismatch of Thermal Expansion?

Accepted Answer

The mismatch in thermal expansion between different materials in a circuit assembly generates significant mechanical stress during thermal cycles. Epoxy resins typically expand at a much higher rate than the copper plated within via holes, creating tensile stress along the barrel of the via. If the temperature exceeds the glass transition temperature of the polymer, the expansion rate accelerates rapidly, increasing the risk of via cracking. Designers select high-reliability resins with low z-axis expansion rates to protect delicate internal connections from these stresses.

Question 3

What is the Reliability Assessment of Thermal Expansion?

Accepted Answer

Solder joint reliability also depends on matching the expansion behavior of the board to that of the component package. Large silicon dies mounted directly to a printed circuit board can experience solder joint fatigue if the expansion rates do not align. Specifying low-expansion laminates resolves this risk in demanding applications.

Thermal Expansion

Dimensional Inflation

Material Mismatch

Reliability Assessment

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