Ask the Experts
August 22, 2011 - Updated
August 22, 2011 - Originally Posted

Unusual Component Lead Contamination

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

Can you offer any comments?

E. W.

Expert Panel Responses

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: liquidus, 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 liquidus 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 been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.

This is an interesting picture and to determine the exact cause of it would be difficult by just looking at the picture. However it appears the pad has pulled off the front of the component, in this case the resistor. It is also evident that the ink on the top of the component is peeling off. The termination on these ceramic components is typically a silver or gold palladium coating onto the ceramic, then a nickel coating then a tin coating. The nickel coating is there to prevent the leaching of the initial metallization during the soldering operation. In this picture the entire metallization appears to have peeled off. For this to happen the component would have had to have major thermal shock to peel it off in this fashion, otherwise is would have dissolve into the solder and leached off the front surface of the component. With the information presented in this picture I would strongly suspect a counterfeit component and faulty construction, not a defective solder joint.

Leo Lambert
Vice President, Technical Director
EPTAC Corporation
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.

There are two strong influences for this type of defects

1. Incoming material quality: Check the component terminal in flurosence X-Ray for Contamination, type of contamination, IMC (Intermetallic Corrosion) or any Air medium presence in between lead and the body, also check for Sn/Pb composition of the terminal if it is leaded component, Check for Sn content if the component is Leadfree component.

2. Soldering Process: if you get only to this type of component or type of packages?

Please do the thermal profile at that particular point and do the correction if necessary, I suspect that the:

* Terminal is damaged because of more heat, it may be because of the oven or may be because of the terminal contamination so that the terminal is not withstanding to the required temperature.

* Also strong suspect on the solder paste volume at that particular pad, if there is a more variation in the volume of the solder paste then because of surface tension this will cause the terminal damage by pulling the terminal at the higher volume side.

Keshava Murthy
Process Engineer
Bosch Automotive Electronics India Ltd.
Keshava Murthy is a Process Engineer in the PCB assembly industry working in Bangalore, India.
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