Methods for Determining Thermal Transitions in Laminated Circuit Board Materials and Their Relationship to Cold Punchability

Materials used in laminated circuit boards must be dimensionally stable at elevated operating temperatures and tough at room temperature to be cold-punchable. Certain polymeric materials with two or more thermal transitions have the desired combination of properties. Two novel methods for determining these transitions were developed. The first utilizes a single cured lamination of the circuit board material in low-frequency dynamic mechanical studies in the temperature range from - 180°C to + 200°C. It is useful in predicting the role of plasticizer content in improving punchability. The second method involves determination of the crack arrest temperature of the complete laminate. It is a close analog to cold punching and can be used to predict safe punching temperatures. Both methods have been correlated with a visual examination of the cold-punched laminates. Two of the transitions observed by dynamic mechanical property studies were substantiated by differential thermal analysis measurements.