Legislative initiatives for the elimination of lead in electronic products continue to create confusion. Manufacturers are not certain to what extent they need to verify compliance. A paperwork trail from component and board suppliers will provide documentation of compliance. What amount of analytical testing will be required to validate compliance? The answer to this question is very dependant on what your budget for testing will be. The legislation as it stands today requires every solder joint to contain less than 0.1% by weight of lead. Testing the entire assembly at one time will not assure compliance, testing 100% of the components will cause your CFO to resign. What testing to perform, and how often is a crucial question that needs to be answered to complete your lead-free transition.

The number of analytical techniques to quantify a concentration of lead < 0.1% are limited. Atomic Absorption (AA) and Inductively Coupled Plasma (ICP) will quantify lead down to sub-100 ppm levels. Both methods are similar in that they require an acid digestion to put the metal into solution. The metal solution is then run on the machine, which produces characteristic radiation that traverses the media. Absorption or emission of the radiation (spectral lines) reveals the presence of the different elemental constituents. As you have probably guessed by this point, AA & ICP are not economically feasible for the enormous quantity of components that populate most electronic products. Its use will be most beneficial in validating lead-free wire, bar and paste solders.

There is a bright side to this story. If your solder alloy is confirmed to contain no lead (through ICP or AA), you need only be concerned with lead concentration on the component and board surface finish. An assumption can be made that the component & board finish will be less than 5% of the total solder joint volume. With this assumption we can now test the components down to a 2.0% detection limit and be assured of compliance in the final product. This jump from a 0.1% to 2.0% detection limit opens up a slew of other testing options. Energy Dispersive X-Ray Spectroscopy (EDS) & Wavelength Dispersive X-Ray Spectroscopy (WDS) are capable of seeing concentrations down to < 1.0%. These methods are much quicker than AA & ICP, but the equipment is nearly as costly making EDS & WDS still too expensive. X-Ray Fluorescence (XRF) on the other hand is much less costly, and calibrated with the appropriate standards will provide resolution down to 2.0%. XRF first reached fame in the electronics industry as a quick, non-destructive means of determining coating thickness for component leads and solder pads. XRF works by bombarding the metal surface with X-Rays, this energy disturbs the electrons in an element and causes them to move from one electron shell to another. When electrons move they eject a small energy packet in the form of X-Rays. The photons are detected by the instrument and counted. The energy (or wavelength) of the X-Rays are characteristic of the element detected & the number detected is proportional to the concentration.

Sounds like the answer to all you problems? Be careful, you may want to conduct some detailed research prior to submitting the PO for one of these machines. Some initial feedback from our customers has indicated that there is a significant difference in capability between models & manufacturers. You should also look at the total cost of ownership. Each metallurgical stack-up will require its own set of standards, one with lead, and one without. Changes (even slight) in the coating or base metals will require the purchase of new standards. Another consideration is that this equipment generates XRays, and is therefore subject to the same registration, procedural & radiation protection requirements of X-Ray inspection equipment. When all factors are tabulated, you may be better off partnering with a lab such as Process Sciences to conduct vendor surveys.

Stephen Schoppe
Process Sciences, Inc.
sms@process-sciences.com
512-259-7070

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