Today’s blog post originally appeared in Circuitnet on August 22, 2011

http://www.circuitnet.com/articles/article_83073.shtml as a response to an Ask the Expert Question. We think it’s worth repeating here as well.

Subj: Unusual Component Lead Contamination

We suspect the issue visible on the attached image is due to contamination on this component lead. We only see this issue on one component type, and only on one side of the component.

Can you offer any comments? E.W.

REPLY FROM PAUL AUSTEN, OF ECD:

Here is one possible cause to check on before you apply the failure to the component.

As with most solder quality problems, it is best to make sure the solder thermal profile, as required for good soldering for you specific solder paste, is being met. Do not assume that a general thermal profile for this board is the same everywhere on the board.

Make sure the thermal profile on or very near each end of this component is as needed. I have heard of components as small as this stand up on one end and then lay back down again during the solder transition into the liquid state (AKA: liquidous, or liquidus) because one end of the part heated faster than the other by a few fractions of a second. By the time the component lays down again, it is too late for best wetting.

To look for this possible time delay in the heating of the component’s ends with your thermal profiling software, make sure the profile peak alignment tool in the profiling software is turned off so you can see instant by instant the temperatures measured at each end of the part through the liquidous point of the solder. If one end is hotter than the other during this time, this may be part of the problem.

The cause of the temperature difference may be because one end of the part was on a pad that had no (or poor) thermal relief compared to the other. Typically, you need both pads of a component to be thermally equivalent. It may be that the board design needs to changed, or it may be as simple as running the board through the oven process turned 90 or 180 degrees to the current orientation.

However, turning the board 90 to 180 degrees may introduce other production or thermal issues on other components. None the less it may be worth trying.

Paul Austen, Senior Project Engineer

Electronic Controls Design Inc

paul.austen@ecd.com

Paul Austen is a 30 year veteran Senior Project Engineer with ECD in Milwaukie, Oregon. Paul has seen and worked with the electronic manufacturing industry from many points of view, including: technician, designer, manufacture, and customer.