Lead Free Assembly and ROHS Compliant PCB Materials

Qualities to consider when choosing a lead-free circuit board material:

Glass transition temperature (Tg), coefficient of thermal expansion (CTE) and decomposition temperature (Td) are key data points to consider when choosing a substrate material for a lead free assembly compatible design.

  • The Tg of a resin system is the temperature at which the material transitions from a rigid state into a softened state. Tg is the material property typically used by the industry to compare the thermal robustness of a laminate. Though a contributor to lead-free compatibility, Tg alone is not sufficient to indicate if a material is suitable for lead free applications.
  • CTE is a measure of the material expansion below and above the Tg and generally expressed as parts per million (ppm). A lower CTE generally indicates increased plated through hole (PTH) reliability. A low CTE is a strong indicator of lead free compatibility and high temperature solder reliability.
  • Td is derived by measuring the weight loss of the sample versus temperature. Td is important when assessing thermal survivability, particularly during high temperature lead-free processes. A material’s decomposition temperature is the temperature at which the material weight changes by 5%.

Lead-Free Technical Papers: