Connector Cleanliness and Flux Entrapment

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Plated through hole connectors can present special challenges when it comes to assembly cleanliness and reliability. Cleanliness of the raw part, processing parameters and chemistry selection can all negatively affect the reliability and robustness of the interconnect system. This article will discuss some common issues and how to resolve them.

Raw part cleanliness

One commonly overlooked source of contamination is the incoming components themselves. The molding process can leave behind mold release agents, mold cleaning compounds or other undesirable chemicals that could affect the reliability of your assembly. Outside of the molding process, handling and packaging have also been identified as possible sources of contamination. This is especially problematic in a no clean application because there is no opportunity in the process to remove those contaminants.

Chemistry selection

If a no clean flux is used in a wave solder process, flux and/or flux vapors can migrate to the solder destination side of the board where capillary energy may draw the material up into the connector body if the pins are not hermetically sealed. This flux will not see adequate heat and can leave behind corrosive and conductive residues. If excessive flux is applied, the residue can interfere with mating pin contact.

Even if water soluble flux is used, problems may arise as well. As with other components, low standoff heights can interfere with the ability of the wash solution to penetrate and effectively clean under the connector, or wash solution may be entrapped and contribute its own set of contaminants.

Processing parameters

In applications where the product is washed, special consideration should be given to the pressure and orientation of the wash spray. Right angle connectors can be challenging to properly clean due to the large surface area masked by the connector body. Additionally, if flux has wicked up into the connector body, spray from above and below will not effectively clean inside the body of the connector.

Plated through hole connectors can present unique processing and cleaning challenges, but with a focus on incoming component cleanliness, careful processing, and wash process optimization, robust and reliable interconnections can be ensured.

Tony Musall is a Project Engineer for Foresite Inc. He is responsible for documenting and preparing samples for the laboratory and performing analytical testing as required.