Process, component or full product re-qualification: leaded to unleaded solder

[Vince]

I was wondering whether you have any experience with moving a Printed Circuit Board Assembly (PCA) from a lead based soldering standard to a lead free soldering standard. Is it possible to do a process based re-qualification of the soldering process only or would you recommend to focus on the PCA as one part of the product? The third option we see is to re-qualify the product as a whole. Each of these appear to demand different types of tests.

At the moment I am looking at it from a form, fit and function consideration (reliability element). As form and fit appear not to be impacted we consider that potentially reliability considerations come into play here. Do you have any experience or are aware of any case studies, standards or suggestions on how to approach this in a concise way?

 

[Miner]

I cannot speak to the FDA regulatory aspects of your questions, but have gone through a conversion to lead free in order to comply with RoHS.

This conversion is a MAJOR issue. It is not easy, and a lot of unexpected problems WILL arise. The temperatures required to process lead free are higher, and some components (LEDs) are borderline in the ability to handle these temperatures. Lead free components and processing are less forgiving than leaded. This results in higher levels of defects and reliability problems until you get your process and product design dialed in.

In summary, do not try to minimize your re-qualification testing.

 

[Vince]

Thank you very much. This is really helpful. The RoHS route is what we are looking into.
We have done a review of the components that are used on the PCA. The max. temperature of the components appear to work well with the higher temperatures of the lead free soldering. It appears on paper that we should be fine.
The main thing we are trying to get our head around is the reliability issue that appears to be always associated with the change. How do we qualify this as we couldn't do a multi year test to see whether certain chemical formations occur, which impact on reliability. Next to the higher soldering temperature is this the second most important thing to look into or are we missing anything here?

 

[outdoorsNW]

In addition to the components, you need to check the max temperature and number of thermal cycles the PCB material can withstand. There still are a few materials available that are not suitable for typical lead free temperatures.

 

[Miner]

I am going from memory because I am not as close to that process as I once was. You may have to redesign your board layout to prevent tin whiskers. Some of the board finishes have a shorter shelf life due to oxidation in which to process them through the soldering operations. Be very careful in the selection and use of fluxes. Lead free does not wet as easily as lead solder and may cause components to shift or tombstone.

 

[Jim Wynne]

In addition to the issue of tin whiskers, when you're experimenting with different fluxes, be on the lookout for solder balls.

 

[outdoorsNW]

Since you are switching solder, you will switching fluxes. For a high reliability application, no clean fluxes are higher risk because certain types can be reactivated if the device is ever exposed to condensation or other some other conditions. I read an article about this but can't find it right now. There are low activity water soluble fluxes (often low activity is why no clean is used in high reliability applications), but they are less common.

 

[Miner]

I remember having reliability issues caused by flux.

 

[msbettyhunt]

I remember having reliability issues caused by flux.

I usually face electronics failure due to soldering flux residue.