August, 2014
www.us-
tech.com
Clean PCBs Aid Reliability of Medical Devices
Continued from previous page
dard enough to prevent failures and can today’s cleaning methods truly clean the boards that are being pro- duced right now? There are a number of myths
circulating in the industry: l
fabrication house are clean. l
with no contamination issues. l
lems and can just be poured onto the board without worrying about heating or the absence of heat and everything will work out okay.
All bare boards coming from the All components are delivered clean Flux will never present any prob-
supporting subsystems were ordered and installed. Test and evaluation procedures were developed and im- plemented to verify the effectiveness of each process. All boards were rou- tinely run through the system both prior to and following the assembly process to ensure that the soldering process was not compromised by any contaminants from the PCB fabrica- tion process and that the PCBs were completely clean of any remaining chemicals from soldering. This cleaning process is com-
While this is not the reality in
manufacturing today, the assump- tion of these concepts presents major issues for manufacturers. A circuit board with hidden residual flux con- tamination may pass quality control (QC) and operate properly. After ar- riving in its operating environment, there may be high humidity and tem- perature swings that generate con- densation that initiates residual flux problems that grow and eventually cause leakage paths that ultimately cause failures. The high-impedance circuits of today’s micropower elec- tronics are even easier to disrupt with stray voltage sources. Washing a PCB following the
soldering process typically produces a board that appears clean. But con- tamination may still be present in areas that are not visible. A conven- tional wash cycle may not be suffi- cient to clean the board. Rather, it may require a combination of chemi- cals, temperature, wash cycles, and timing to get some boards really clean. “The cleanliness of a printed
board can directly impact the effec- tiveness or quality of an assembled printed board,” said John Perry, IPC technical project manager and staff liaison to IPC’s Bare Board Cleanli- ness Assessment Task Group. “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 ex- tremely important.” Digicom Electronics has used
significant resources to research these issues. In many instances, it was found that a combination of com- paratively minor points, when com- bined, pointed to processes that sim- ply do not work as well in an up-to- date manufacturing environment, al- though they provided acceptable re- sults in the past. Minor changes in component
packaging design, materials, CAD/ CAM software, board fabrication, and chemistry have combined to slowly change the robustness of the manufacturing process. Even the best intentions have often unwitting- ly created the potential for defects to occur in electronic circuits in ways not previously possible. It was only through a comprehensive evaluation of all materials and steps in the man- ufacturing process that root causes of potential problems were discovered. Armed with a clear picture of poten- tial problem areas, much effort was expended to find solutions to each problem. At Digicom, new equipment and
pletely “green.” De-ionized water from polishing tanks is used and recycled. Filters catch the solids while powerful blowers ensure that harsh chemicals don’t migrate past the holding tank. Clear windows on the equipment en- able the operator to monitor the entire process. A refractometer checks the stability of the mix in the tank to veri- fy that it’s not compromised. The dis- charged liquid is completely environ- mentally friend ly. Processes were then thoroughly
tested, evaluated for effectiveness, and ultimately validated as a stable process. Independent tests showed that circuit boards that went through this cleaning process tested 75 per- cent cleaner than the 10-2 µg/in.2 specified by IPC as its highest level of cleanliness. In addition, a lab analysis for ion contamination found zero levels of NaCl ion contamination on the assembled boards. This level of cleaning eliminates
failures caused by board contamina- tion. Products are less susceptible to corrosion-induced failures, thus re- ducing the need for maintenance or repair. In addition, the cost savings to companies, especially those with military, aerospace and medical de- vice applications, are considerable. Contact: Digicom Electronics,
Inc., 7799 Pardee Lane, Oakland, CA 94621 % 510-639-7003 E-Mail:
info@digicom.org Web:
www.digicom.org r
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