Technical Data Package Verification for Component Process Change Notices
Verifying component process changes requires validating raw S-parameters, mechanical coplanarity, and firmware regression logs against baseline specs.
Substrate Tg Mismatch
Meaning
Discrepancy in the glass transition temperatures of different materials used in a multilayer printed circuit board can cause internal damage when the board is heated. This issue, referred to as substrate tg mismatch, occurs when layers expand at different speeds as they pass their transition points during the soldering process. The resulting stress can pull the layers apart or break the internal copper connections.
Managing this behavior is necessary when designing boards that must survive high assembly temperatures.
Material Behavior
Passing the transition temperature causes the resin in the board to change from a hard state to a soft state, increasing its expansion rate. If one layer reaches this soft state before the adjacent layers, the difference in expansion creates high stress at the boundaries. This behavior can lead to delamination and hidden failures that are hard to detect during final testing.
Reliability Testing
Temperature cycles are run to check how well the multilayer board can withstand these thermal stresses without failing. Technicians use microsection analysis to look for internal cracks or layer separation after the boards have been through the test oven. These reviews help verify that the chosen material combination is stable.
Design Adjustment
Designers reduce the risk of failure by selecting materials with similar transition temperatures for all layers of the board. They also place copper vias and power planes evenly to help distribute heat and reduce localized stress. This work is essential for ensuring the board remains flat and reliable during assembly.