Jim, There is a potential hidden defect related to solder mask webs between fine pitch pads. Not all suppliers and LPI combinations can successfully place mask webs between fine pitch pads. The potential defect starts with the adhesion of the webs. If they are not fully attached to the laminate, they will break off during handling and processing. The broken web pieces are so thin and light that they stay on the surface of the board but of course in various new locations. Any that come to rest on SMT pads can become a reliability issue. Just one of these pieces laying within the solder area when an SMT component is placed can lead to an open or intermittent lead connection. The web pieces are thick enough to raise the component's lead off of the pad. Since solder mask is designed to repel solder, the web fragment does just that, leaving a poor or sometimes open connection on that pad. A visual inspection of the bare boards by a skilled inspector can detect this potential. These poorly attached webs will also fail the tape test. Properly attached webs will always pass the tape test. There are suppliers who have LPI processes that can successfully provide mask webs between the fine pitch pads. Concerning the actual value of the webs, the experience here has been with a good paste screen printer, the webs are not necessary. When properly included, the webs are nice to have but they are not needed to avoid solder bridging. Norm Dill [log in to unmask] ---------- From: TechNet-request To: TechNet Cc: spendow_jim Subject: Soldermask webs Date: Wednesday, May 08, 1996 11:49AM Some designers make an effort to maintain a web of soldermask between the solder pads on SMT devices, where pad spacing permits. When the spacing of fine pitch devices preclude the web, it is omitted. I have heard that the webs are used to reduce solder bridging. Thinking through this issue, I find webs being used where pad spacing is large enough so as to make solder bridging unlikely, while webs are omitted when the pad spacing is close enough to make solder bridging most likely. I am interested in any factual data that supports the reason for, or the value of, soldermask webs. Thank you in advance for your response. Jim williams [log in to unmask]