Standard Microsection Inspection Procedures for Class Two and Class Three Annular Rings
Class 3 microsections require zero inner layer breakout and 0.050 mm minimum ring width, whereas Class 2 permits 90-degree breakout if conductor spacing holds.
Solder Float 288c
Material Resistance
Thermal stress tests evaluate the ability of a printed circuit board to withstand the heat of wave soldering or rework without delamination or blister formation. The solder float 288c procedure subjects a small specimen to molten alloy at a specific temperature for a defined duration, typically ten seconds. This test mimics the extreme conditions of assembly and reveals weaknesses in the bond between the resin and the reinforcement.
Procedure Step
Preparation begins with baking the sample to remove moisture that might cause a false failure through steam expansion. The specimen then floats on the surface of a solder bath held precisely at the target temperature. After the specified time, the operator removes the board and allows it to cool before cleaning and inspecting the surface to identify any visual defects.
Microsectioning often follows to check for internal cracks or barrel separation.
Failure Mode
Evidence of outgassing or separation between layers constitutes a failure of the material or the lamination process. A board that passes the solder float 288c demonstrates that the resin system is fully cured and the surface finish is compatible with high temperature processing. These results provide confidence in the long term reliability of the product under field conditions.