Companies that do business in Europe have been complying with the Removal of Hazardous Substance (RoHS) directive mandated by the European Union since 2006. Companies that sell only within the United States may still be making printed circuit boards that do not comply. These companies may be required to meet the RoHS mandates or other similar mandates that have been adopted by some states. Many entities, such as the government, that were originally exempt from RoHS requirements are now finding it in their own interest to convert because most new technology components are released only in RoHS form.

The RoHS requirements have implications for the printed circuit board, components, and solder. All three of these items must comply or the assembly will fail to meet the standard and the printed circuit board assembly (PCBA) cannot be sold into these markets. The single item that has the largest impact to the manufacturer is the lead free solder. The printed wiring board and component leads must have plating that matches the lead free chemistry. There isn’t a “drop in” replacement for the PbSn solder and the change to lead free impacts many things including reliability of the assembly, longevity, and resilience of the assembly where temperature and vibration are considered. The lead fee assembly may also be more susceptible to damage during rework due to the higher temperatures required for reflow.

The conversion to RoHS typically starts with the bill of materials (BOM). Each line item on the BOM must be researched and where necessary, changed to RoHS compliant components. Most parts will need to be changed. In some cases the component manufacturer will make both compliant and non-compliant components in the same package which will make the conversion less painful. Care should be taken to make certain that both parts have exactly the same characteristics. It is more common to find that a component is made in only one form and that another manufacturer must be found for the RoHS component. Many times an exact replacement isn’t available and the PCB must be changed to match the new components.

The printed circuit board changes include both the substrate and the plating used for the pads. There are many options for plating including organic surface protectant (OSP), immersion silver (IAg), immersion cold (ENIG), and lead free HASL. Each has strengths and weaknesses and the choice must be made carefully. OSP is an excellent choice for most lead free assemblies but any areas where plating must remain after reflow will have to be coated with a second plating (typically ENIG) to protect the pads. This can add considerable cost to low volume circuit boards. IAg has good properties where solderability is concerned but it has a very limited shelf life, almost no ability to be reworked and special care must be given during handling. ENIG is prone to a condition called “black pad” and in some cases the meager amount of gold used in the plating can migrate to the solder, polluting it and making the solder brittle. It’s important to understand all of characteristics of the plating choices before making a decision.

Substrates that are designed for RoHS assembly processes are typically more brittle then those used for PbSn. This has implications for the resilience of the printed wiring board (PWB). It also adds complexity to some aspects of the circuit board fabrication process such as scoring.

The assembly process is significantly different where reflow is concerned. Much higher temperatures are required for the proper reflow of most lead free solders. A balance must be struck between using temperatures that are high enough for proper reflow of the lead free solder and the damage high temperatures can cause to the assembly.

The change to RoHS compliant PCBA’s impacts every aspect of designing and building printed circuit boards. It is deceptively complex with few if any drop-in solutions. Most companies experienced problems when they were first required to meet these standards but today they create RoHS compliant boards with much the same confidence as they had when designing and building legacy PbSn boards. The learning curve has been steep but the knowledge base on this subject is constantly growing. Companies that are just now deciding to make this change should avoid experiencing the same difficulties as the pioneers of this technology by acquiring experienced professional help with their conversion efforts.