A quick determination of a stencil wiping roll’s ability to withstand fiber detachment and consequent contamination of circuit boards during the printing process
The goal of this test is to select an SMT stencil cleaning roll that is free of weak linty paper fibers that can break ways. Using a lint-free roll such as the GREEN MONSTER can help prevent damage to equipment, defects, bridges, blocked apertures, low transfer efficiency, and solder contamination.
Contaminated PC boards are a common problem. While the contamination itself is often thought of as a mystery, the cause may actually come from the stencil wiping roll itself. This is largely due to the sticky solder paste and sharp edges of the stencil’s apertures.
The stencil wiping roll is supposed to clean the stencil in an attempt to prevent contamination. However, some stencil wiping rolls often leave behind pieces of its material on the stencil, subsequently contaminating the PC board. When these contaminants pass through the oven, voids will occur.
One can determine the probability of contamination with an easy test of the stencil wiping roll. The test is called the “Tape Test”. It is a quick and simple experiment that will save any company money by not having to repair contaminated boards. It will also help any company in determining which stencil wiping rolls are acceptable.
Stencil Cleaning Roll Tape Test Procedure
- First, cut off a piece of scotch tape or black electrical tape about 2 inches in length.
- Place the strip of tape along the surface of the stencil wiping fabric.
- Once the tape has adhered to the surface, pressure must be applied. The pressure should
- be applied in an even fashion. To ensure that the pressure is equally applied roll a 1,000gm calibration weight over the taped surface. If a weight of this size is not available, a seam pro (used for wallpaper seam attachment), a full can of soda or any tool that will provide equal weight distribution can be used. In some cases, simply using a finger will be acceptable.
- If Scotch tape is used, place it on a black surface and observe the mount of fibers pulled off with the naked eye or better yet a magnifier. This test can easily be quantified by counting fibers and particles under magnification.
- For the best determination, repeat this step for front and back sides of the wiping roll’s
Important! This test is only valid when comparing fabrics.