All four of these factors impact the success/failure of the screen printing process
Written by HC AUTOMATOIN / Read 44 times
The short answer to this question is: All four of these factors impact the success/failure of the screen printing process. Both paste volume and print alignment are important. The paste volume determines the success or failure of the solder joint after reflow.
Excess volume may result in bridging, solder balling, and tomb stoning of components. Not enough volumes create insufficient solder joints. Both excess and insufficient volumes will require costly rework. Print alignment is a key factor, especially for smaller component technology (fine pitch, micro BGA, 0201, 01005). Registration issues on these small packages will cause solder bridges and solder balls.
These issues are intensified with the use of Lead Free solders. When printed off pad, lead free solder will often create solder balls, rather than pulling back to the pad. The stencil apertures are an excellent way to control the volume of paste deposited on the board.|
The correct combination of aperture design and stencil thickness compensate for lead to pad compatibility issues, and result in robust solder joints when all processes are correct.
The machine setup drastically effects the performance of the stencil. The correct combination of print speed, pressure, and snap off ensure proper paste release from the stencil.
If any of these are out of adjustment, the paste may not separate properly from the stencil, affecting the volume deposited on the board. The paste deposition is critical. There is still part placement and reflow ahead.