NPL. Reliability testing workshop

NPL

Reliability testing workshopKeywords:NPL, Reliability testing

A new workshop "Improving Design and Process through Reliability Testing"has been announced by NPL, to be held on site at The National Physical Laboratory, Teddington on 18 October 2001.

The reliability of electronics products is of paramount importance. This is highlighted by the most common questions asked of NPL and the huge DTI support for research in this area. The wears out or failure modes of electronics products include electro-migration (surface dendrites), corrosion, or electro-mechanical (crack formation, fillet lifting). NPL has been investigating these phenomena in the context of electronics.

The Electronics Interconnect group has collated raised concerns about electronic reliability and uniquely the workshop is based directly around these issues, drawing on NPL's wide experience and knowledge in the field, as well as new relevant research.

Delegates will be:

• assessing reliability of circuit assemblies;

• identifying the causes of poor reliability;

• learning how design can increase reliability;

• discussing the use of analytical methods;

• learning how industrial techniques are implemented;

• gaining practical experience.

The aim is to transform the way delegates' organisations perform in the future.

NPL has released their Report by Deborah Lea, Fredirikus Jonck and Dr Chris Hunt, investigating lead-free soldering technologies. This study was undertaken into the solderability of combinations of three lead-free solders (SnAgCu, SnCu,SnAg), three fluxes, and five lead-free printed circuit board pad finishes(immersion Sn, immersion Ag, HASL SnPb, OSP, and NiAu). The wetting characteristics of the various combinations have been measured using a wetting balance.

It is evident that, to obtain acceptable wetting, careful choice must be made of both the pad finish and flux. In general, boards with an OSP finish gave the best wetting results at all superheats and for all the lead-free solders studied, whilst the immersion tin finish gave the poorest wetting characteristics. The results also provide valuable information for PCB designers, allowing them to predict the wetting forces as a function of pad size. The data indicated that there is a simple relationship between pad area and wetting force, irrespective of the solder type.

Moreover, there is a linear relationship between pad width and wetting force or wetting time. In both cases only immersion Ag pads and an activated flux were studied. The behaviour is similar to that of conventional SnPb, if allowance is made for the superheat.

A similar paste "dot" coalescence test has been shown to be valuable in ranking various process combinations. Its simplicity and inexpensive nature make it an attractive option for in-house process evaluation.