Provisions for clean PCBs
The cleanliness level of a completed Printed Circuit Board is vital to the life cycle of your end product.
Contaminated PCBs can deteriorate insulation resistance as well as lower dielectric strength.
IPC-5704 provides industry guidance on cleanliness testing for both product acceptance and process control, ensuring reliable equipment and chemistries.
“The cleanliness of a printed board can directly impact the effectiveness or quality of an assembled printed board,” explains John Perry, IPC technical project manager. “Residues increase the risk of field failures or can electrically impede a printed board’s function, so having acceptance criteria for various levels of testing as well as direction on how many samples should be tested is extremely important.”
C-7000 Cleanliness Requirements for Unpopulated Boards
The cleanliness provisions for IPC-5704 have been adapted from Delphi’s C-7000. A bare board specification based on ion chromatography, C-7000 has been successfully used for 10-15 years and is consistent with recommended cleanliness levels from CSL/Foresite, PAL, and Rockwell Collins.
Like the industry standard Ionograph, Ion Chromatography measures total ionic contamination. However, and unlike an Ionograph, Ion Chromatography provides a breakdown of the levels of each individual component of ionic contamination.
Providing solutions for Printed Circuit Boards with High-Reliability Applications means accommodating the enhanced specification required. As a result, we employed a multi-step process adjustment to ensure bare board cleanliness. A primary contributor to high ionic contamination levels is the flux used in the HASL process, which can become entrapped in soldermask pores.
To close these pores, SEC installed a UV oven in line with our soldermask developing and baking line. The UV “bumping” completes the soldermask cross-linking process to close the pores–ensuring the flux remains free on the PCB surface and no longer entrapped within the soldermask.
Custom Post-HASL Line
Saturn designed and built a custom post-HASL cleaning line for the sole purpose of removing the flux from the board’s surface.