A prerequisite for a sound solder process is that the components involved are solderable. An important aspect for solderability is the wetting ability or wettability of the components by the liquid solder. The wetting balance test method is the most universal test for the measurement of the wettability of the component surfaces to be soldered, both, leaded and surface-mount.
The test can be performed under process conditions, using the same flux and solderbath temperature as used in the real process. This will give a direct indication for the solderability of the product in the solder process.
In most cases however the test is done at a 10 - 15°C lower solderbath temperature, with the use of a special low activated test flux. If the solderability requirements during this test are met, one has a certain guarantee that also after a reasonable storage time the products can be used in production without solderability problems.
The wetting balance test can also be used to determine the thermal solderability or the specific soldering distance for leaded components. The wetting balance test is not developed for testing PCB's. For testing the solderability of PCB's Rotary Dip test is still the most adequate test method.