June, 2019

Page 53

Drying: A Critical Step in PCB Cleaning S

By Sheri Pear, Marketing Communications Specialist, MicroCare Corporation

uccessful benchtop cleaning of PCBs should not be underestimated. Clean ing is critical for PCB manufacturers

as smaller, more densely populated circuit boards, like 3D stacked PCBs and complex ball grid arrays (BGAs), become standard features in the electronics industry. Each new generation of a product must outper- form its predecessors, and as the size of devices continues to shrink, the need for increasingly better cleaning choices and the way in which they are achieved becomes more important. There are four steps to successfully

cleaning PCBs. Wet, scrub, rinse, and dry. The wet, scrub and rinse operations are obvious. First, wet the board with a pure cleaning fluid. Next, scrub it using a good quality scrubbing brush. Then, rinse it off with more clean fluid. However, the final step of dry- ing the PCB is often overlooked or in some instances, completely left out of the cleaning plan. For reliable performance, circuit

boards must not only be clean, they must also be dry in order to operate correctly. If moisture remains on a PCB surface it can result in a variety of problems. These can include corro- sion, electrochemical migration, delamination, and dendrite growth. There is also the issue of blow holes occurring by the PCB outgassing dur- ing soldering, as well as adhesion problems with conformal coatings later in production. Modern PCBs often have bottom

termination components, such as land grid arrays (LGAs) and quad flat no- leads (QFNs) with very tight standoff heights. Moisture can get trapped under these components, making dry- ing even more complicated. Depending on the cleaning

process used, there are a number of different methods to dry PCBs. Some manufacturers may use inline aqueous cleaning or benchtop scrubbing, while others use vapor degreasing. Whether using heat, vapor, wipes, or com- pressed gas, there is a successful dry- ing method available to ensure PCBs are not only clean but also dry for opti- mum reliability and performance.

Dry at the Benchtop

Wipes. During benchtop cleaning, one of the most common methods to dry a PCB is to use a simple lint-free wipe. This can be used to wipe away the excess spray of cleaning fluid on a circuit board or as a method of cap- turing fluid under low-surface mounted components by gently push- ing the wipe underneath. Wipes are a quick and effective

way to dry the PCB without leaving lint behind. But is the correct wipe being used for maximum drying effi- ciency? There are many factors to con- sider when selecting a lint-free drying wipe, from absorbency and material to the packaging it is housed in. The most important feature to

look for when choosing a drying wipe is its ability to absorb the type of moisture encountered. For example, some wipes will absorb cleaning flu- ids, but will not absorb water. It is essential to match the type of wipe absorbency to the contamination to be removed. Another factor to consider is

what the wipe is made from, as this can affect just how clean and dry the PCB will be. Non-woven wipes are

See at ATX/MD&M East, Booth 1248

made without glues or binders, therefore, do not leave residue on the surface being cleaned. This results in a cleaner PCB. Another way to limit fiber contamination is to choose pre-washed wipes or wipes with finished or heat-sealed edges. These work well to eliminate contamination. Although not an obvious consideration

Drying a PCB correctly after cleaning can contribute to its dependability and performance.

when choosing a wipe, the packaging is one that is important when choosing a drying wipe. Some manufacturers require wipes to have static-dissipative properties and to be packaged in electrostatic discharge (ESD) safe wrappers.

Continued on next page

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