Did you ever wonder why you have specific oil to run in your car?
As most people know, your car or truck's engine takes a specific "weight" oil (example: 15w-30), but using the wrong weight oil for the wrong application can cause serious issues, such as oil pump failure, cavitation, and a decrease in engine performance due to it working harder.
This can be related to having the right viscosity solder paste for the certain aperture size, to decrease the amount of slump, when printing on a circuit board.
What is slump? Theoretically, a solder paste's sidewalls are completely straight after the paste has been deposited. But, after time, those sidewalls will begin to round out, increasing the surface area of paste deposited on the circuit board, and compromising the print integrity.
- Solder paste that is too thin (low viscosity) can cause slump which will lead to bridging after through the re-flow oven. The area ratio plays a factor on this because this allows the correct thickness to choose for a stencil.
- Having too thick of a stencil with the wrong paste viscosity will cause slump depending on the aperture size.
Calculating area ratio and staying within typical guidelines will give the best first-pass yields.
-John