Lead Free Manufacturing and Assembly
Historically, Lead Free initiatives were driven by technology and design requirements. Presently, new green board legislation is driving the elimination of lead in circuit board manufacturing and assembly. Manufacturers and assemblers of printed circuit boards must now take into account: technology, design, environmental, legislative, and final destination when selecting materials for Lead Free products.
Environmental legislation is no longer a dictated by individual countries. The awareness of the need to eliminate lead from the environment is driving countries to enact legislation to enforce this on a global scale. While many countries have drawn up their own set of initiatives, many are adopting additional initiatives from other countries as well. Following are some of these initiatives:
In 1998, Europe introduced legislation called WEEE (Waste Electrical & Electronic Equipment Directive). This is to ban lead use on all electronics by Jan 1, 2006.
WEEE Directive (Waste Electrical and Electronic Equipment)
Multicircuits can build PCB boards for you that are halogen free and meet WEEE requirements. Let us know your requirements when you request a quote.
RoHS Compliant (Restriction of Hazardous Substances)
- ROHS member states shall ensure that electrical and electronic products marketed after July 1, 2006 contain no lead, mercury, cadmium, hexavalent, chrome, polybrominated biphenyls or polybrominated diphenyl ether.
- Multicircuits can build PC boards for you using non-leaded surface finishes that are RoHS compliant. Let us know your requirements when you request a quote.
- 1998 Japanese Industry associations developed a lead free roadmap.
- Voluntary efforts made by many large Japanese OEMs
United States of America (USA)
While the United States does not have firm plans to ban lead in electronics, other parts of the world are rapidly moving to enact legislation.
- Lead is permitted for electronics use.
- Lead is banned in paint, food cans, light bulbs, plumbing solders.
- Continued pressure from Environmental Protection Agency (EPA) to reduce lead use.
- Lead is categorized as a hazardous material.
In the discussion of lead free manufacturing, priority is often given to the replacement of Tin/Lead or Solder as the metal finish. However, there are several other elements of the printed circuit board and the assembly process to consider. Laminates can play an important role in successfully converting a process to lead free. Some considerations to keep in mind are:
- All laminates manufactured in the USA comply with RoHS by not using polybrominated biphenyls or polybrominated diphenyl ether.
- Other non-classified bromines are used as the flame retardant to meet UL's 94 V-O requirement.
- With "Green Board" gaining popularity for its Halogen Free characteristics, other chemicals such as Phosphorus may be used which can cause additional warpage issues because it is very hydroscopic.
Higher Tg Material
- As reflow and wave temperatures increase by 15-25 degrees Celcius, standard 140 Tg laminates may not be sufficient.
- As the layer counts increase, particularily over 8 layers, materials with higher Tg and Td values will help reduce the chances of delamination, intermittent opens, and warpage.
Bow and Twist (warpage concerns)
Higher assembly temperatures will cause more bow and twist on the PCB causing possible assembly issues.
If your application requires controlled impedance or high speed frequencies, you need to work with your pcb manufacturer to carefully select a laminate to satisfy both your electrical and lead free requirements.
Three major types of flux are compatible with lead free technology: OA, RMA, No clean.
- Flux must be compatible with the alloy you select.
- Balance the temperature of activation with the lead free alloy melt temperature.
- Application can be sprayed, foamed, dipped, or brushed on.
- Flux must be easily cleaned.
- Cleanliness issues will become critical as more assembly uses no clean fluxing.
Reflow temperature concerns:
- Current equipment will probably work (multizoned convection oven)
- A 235-260C peak temperature is needed which can cause added stress on both the oven and circuit board.
- Some situations may require a Nitrogen blanket to ensure good solderability.
- A ramp-to-spike profile seems to work best. However, every shop is different and you will have to experiment with the options that work best.
- Voiding becomes more of a concern
- The time above 217C is approximately 60-75 seconds.
- The soak time at 150-200C is 60 to 90 second or about 1.5C/sec
- Other application issues include: stencil life, aperture release and print definition.
- Lead Free Paste does not wet out as far as tin/lead solder.
- Operators need to take this into account when running a lead free line.
- Shelf life on lead free pastes is typically shorter than tin/lead.
- Paste is typically thicker and the printable tack force is generally greater. The speed may also need modifications.
- Cleaning is critical in any process, but even more so with lead free.
- Pot temperatures of 260-275C are needed, but if you choose a tin rich alloy, it could eat away the inside of the solder pot.
- A dedicated line is the best choice, because any leaded components or HASL circuit boards will contaminate the alloy which will have to be dumped.
- Care must be taken to make sure the flux is compatible with the wave
- A Nitrogen Blanket may be needed to ensure a reliable solder joint.