How Do You Clean PCB Assemblies?


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As part of this issue's cover story, p.6, we queried readers about your PCB cleaning habits. Cleaning equipment is a significant investment for an SMT line, and the cleaning materials, water treatment, and other recurring costs can also impact a facility's bottom line. We wondered if assembly houses are getting the most return for their investment in cleaning systems, and how cleaning was adopted. What assemblies do you clean? How often do you clean PCB assemblies? We discovered that, while most participants in the survey do, not surprisingly, have cleaning as part of their SMT line, this is where the trends stop.

Nearly half of the readers that participated in the survey (48.9%) perform prototype and low-volume electronics assembly. The next largest group does mid-volume manufacturing (38.1%) and the remainder (25.0%) run high-volume SMT lines. This is a fairly balanced representation of the SMT assembly market, with respondents from the flex circuit assembly sector, EMS providers, telecom OEMs, solar cell producers, aerospace electronics engineers, and more. Reader survey respondents make everything from harsh environment electronics to cell phone assemblies to microelectronics for medical instruments.

Not every electronics manufacturer cleans all assemblies equally, either. We can extrapolate that assemblers either clean very few jobs, less than a quarter of their total production, or nearly all of their jobs. Of the responses we received, 35.2% of manufacturers clean very few jobs. At the other end of the spectrum, 30.2% are cleaning 75% or more of their production boards. In the middle group, 34.5% of respondents clean around half of their jobs. We expect that this division depends on the reliability ranking of the respondents: high-reliability manufacturers might clean 100% of their assemblies, whereas a high-mix EMS provider might only clean circuit boards to meet the specs of two small customers. It may also represent a shift in the perception of cleaning as relegated to the military/medical sectors. Companies cleaning less than 50% of their jobs may have just begun using cleaning steps for some products, where before they wouldn't have cleaned any assemblies. In this case, cleaning system utilization could be improved by collaborating on process optimization with cleaning product suppliers.

We didn't expect the answers we received for the last question on the survey, "Do you clean no-clean assemblies?" Surprisingly, the majority of respondents (55.3%) do put no-clean PCB assemblies through the cleaning step. Why is this? Is no-clean solder/flux not successfully providing reliability by encapsulating contaminants? Are process specs set up without considering the effect of cleaning on no-clean, assuming that cleaning will always improve finished assembly quality?

We'd like to hear your thoughts on the subject. Email SMT at mcourtemanche@pennwell.com, and fill us in. SMT

Meredith Courtemanche, Executive Editor

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