RoHS vs. Lead Free Assembly
It is easy to mis-interpret the relationship between RoHS and Lead Free Assembly. Lead Free Assembly has been around for decades in limited applications. RoHS came about when the European Union passed a directive known as WEEE. WEEE or Waste of Electrical and Electronic Equipment (2002/96/EWG) regulates the end of life disposal and recycling of electrical waste. The legislation states that producers are responsible for waste and financing its collection. Users from private households should be allowed to recycle products free of charge. To reduce recycling costs the restricted or banned materials, manufacturers are striving to remove these substances from their product. This is where RoHS comes in.
RoHS or Restriction of Hazardous Substances (2002/95/EWG) prohibits the use of the following substances:
- Cadmium CAS# 7440-43-9 Set Limit: 100 ppm
- Hexa-valent Chromium CAS#: 18540-29-9 Set Limit: 1000 ppm
- Lead CAS#: 7439-92-1 Set Limit: 1000 ppm
- Mercury CAS#: 7439-97-6 Set Limit: 1000 ppm
- Polybrominated Biphenyls (PBB) CAS#: 13654-09-6 Set Limit: 1000 ppm
- Polybrominated Biphenylethers (PBBE or PBDE) CAS#: 32534-81-9 Set Limit: 1000 ppm
It is unrealistic to expect that these compounds can be completely removed from electronic equipment. Some the the substances are naturally occuring elements. Trace amounts of Lead may be found in tin ore. Reference: http://bulk.resource.org/gpo.gov/register/1996/1996_4817.pdf for more information. The dirty little secret in the printed circuit board industry is that trace amounts (very little) of Lead is commonly used as a stabelizing agent in both electroplated copper and Electroless Nickel and Immersion Gold processes. The amount is soo small that it only shows up as a few ppm on the finished printed circuit board. You shall even find trace amounts in Immersion Tin. Pure lead free samples are very expensive and may typically be found only in a laboratory. The point is that we can never have commercial grade lead free products that are 100% lead free. Hence the set limits and not a complete prohibition.
RoHS was originally implemented on July 1, 2006. DecaBDE and Octa-BDE were added to the list of restrictions in 2008. This legislation effects commercial applications of electronic equipment. Medical and military products have been granted a waiver till 2010. Medical and military components are life and death applications. With a eutectic solder joint consisting of Tin(63%)/Lead(37%) we know what happens to the solder joint. The copper tin inter-metallic bond grows and strengthens over time after soldering. We have decades of information supporting this fact. With Lead Free Solders we just don’t know what happens over time. We don’t have the data gathered over time to know what happens. The industry has been used as a giant crucible to work out the bugs in the manufacturing and assembly process. The jury is still out on the reliability of lead free solder joints over time.
NOW TO THE POINT OF THIS POST!
Lead Free Assembly has become common place as a result of RoHS. Some designers believe that if they specify RoHS compliance on a print that they shall automatically receive boards that are Lead Free Soldering compliant. This is a mistake. RoHS only sets limits on lead in a sample. Any printed circuit board can be RoHS compliant provided the final finish is changed from eutectic tin/lead solder to a lead free solderable finish such as ENIG or Immersion Silver. Changing to a lead free finish does not mean that the pcb can survive a high temperature lead free soldering process. RoHSimplies but does not require Lead Free Soldering. For example, press fit assembly techniques require no soldering.
A printed circuit manufacturer shall build the part only as specified. If laminate material that is compliant with high temperature soldering is not specified on the fabrication drawing, don’t expect the design to be built on it. In this cut throat age of low pricing for printed circuit boards, a manufacturer shall only quote, build and ship pcbs as specified. I know many designers that have lost their jobs for making this mistake. They only specified RoHS compliance on the fabrication drawing. The pcbs were build on standard FR4 that were not lead free soldering compliant. The pcbs were RoHS compliant and met all print requirements. The pcbs were assembled through a lead free soldering process. The pcbs either delaminated at assembly or failed in the field months later. The financial loss was typically in the five figure range. Can your job survive a five figure loss?
There are some designers that knowingly specify standard FR4 for lead free soldering applications. These are typically simple single and double sided designs. The designers that I am associated with work for companies that have invested the time and effort to prove out what they can and can’t do. Their design and assembly process have been tested and verified to have acceptable yields. On their more complex designs they specify lead free soldering compliant laminate. The compliant materials are much more expensive. They build so many parts that if they can save a dollar here and there it turns into more profits for their company. Their companies have made the up front investment to gain cost savings later.
For more information on how to specify lead free assembly compliant laminates please see my post located at http://www.pcbdesignschool.com/2009/01/05/sample-fabrication-drawing-notes/