IPC TA-724:1998
$32.50
Technology Assessment Series on Cleanrooms
| Published By | Publication Date | Number of Pages |
| IPC | 1998-04 | 197 |
The continuing trend to finer features on PCBs increased the negative effect of particles on board yields. Cleanrooms provide a logical way to reduce the effect of particles, and are more critical as finer lines are required. Cleanrooms have been used since at least the 1970s to make printed circuits, but some boards are still made today without them.
What level of cleanroom is required to make printed circuits? Unfortunately, no easy answer exists. Clearly the size of the particles that can cause problems for PCBs are larger than the concerns of the semiconductor and related industries. Therefore, the requirements are quite different.
For PCBs, particles below 15 microns typically will not cause defects, so cleanroom classification based on the concentration of 5 micron and smaller particles does not directly correlate with PCB requirements. This produced a problem for creating this Technical Assessment.
Most of the papers are for semiconductor and other industries that have finer requirements. This first section, however, does include the best articles on cleanrooms and their application to the PCB industry. The critical areas for cleanrooms are photoresist application, photoresist and soldermask exposure, phototool manufacturing, and multilayer lamination.
Articles have been published and included in this assessment for ail but multilayer lamination. Resist and phototool exposure, which require cleanrooms the most, are the areas considered most critical to particle contamination. Clearly, the particles that cause problems at exposure are large enough that they do not stay airborne for long. So, they will not be removed by the cleanroom HEPA filter system once they are deposited on a surface. Therefore, surfaces around the exposure units, as well as the actual boards and phototools, must be cleaned regularly. This is much more critical than the specific cleanroom classification. For this section and others, the papers are organized with general and basic topic articles in the beginning followed by specific and detailed topic articles.
