One of the first things that I learned with my boat was that the engine pumped lake or river water in for cooling, and then back out again. This would normally have been fine, but since I planned on also boating in the saltwater of Puget Sound, I was advised to install a fresh-water cooling system. This new system still pumped in the seawater, but only to cool the internal coolant which was then circulated through the engine. Although it was an added expense, it protected the engine from exposure to the corrosive effects of saltwater.
Protection from substances that can cause harmful effects has now become a goal for the PCB manufacturing industry as well. For years, electronic components have been soldered onto printed circuit boards using solder with a lead base. To protect the environment from exposure to lead and other harmful substances, regulations are now in place for certain areas to restrict their use. Here’s more information on what lead free PCB manufacturing is, and why it is important.
The Importance of Lead Free PCB Manufacturing
For the last 17 years, over half of the countries comprising the European Union have adopted the “Restriction of Hazardous Substances Directive,” more commonly known as RoHS. By July 2006, this directive put restrictions on certain hazardous materials used in the manufacturing of electrical and electronic devices produced for the EU market. Since printed circuit boards are used in virtually all electronic systems, this directive applies directly to the assembly of PCBs.
Although there are many areas of the PCB manufacturing process that are affected by the RoHS restrictions, the most obvious change is in the type of solder that can be used. Traditionally lead-based solders are used in the assembly of a circuit board. To be RoHS compliant, however, this solder must be replaced with lead free variations. In addition, other substances such as mercury and cadmium must also be restricted in order to achieve RoHS compliance.
To manufacture RoHS compliant products requires that the PCB contract manufacturer must be fully versed and practiced in all of the regulations of the RoHS directive. This becomes even more important when the manufacturer is doing both RoHS and traditional non-RoHS assembly. In that case, chemicals and processes must be kept separate in order to ensure that there isn’t any cross-contamination between the two processes. There’s more to manufacturing lead free PCBs than just switching solder types though, and PCB CMs must be careful to follow all of the necessary requirements and procedures.
RoHS Compliant PCB Manufacturing Details that You Need to Know
There are three main areas of manufacturing that are affected by the lead free process; solder melting temperatures, moisture in the manufacturing process, and PCBA cleaning. Let’s look at these in further detail:
- Temperature:Where traditional lead-based solders melt between 180℃ to 190℃, lead free solders melt at higher temperatures, 220℃ to 240℃. This difference puts a greater amount of stress on the bare boards as well as the components that will be assembled to them. The coefficient of thermal expansion (CTE) of lead free manufactured board is accentuated due to the higher temperatures, and can result in more PCB failures than in boards manufactured in a regular lead process:
- Circuit board materials must be chosen based on their temperature attributes. The laminates that are used in the regular leaded process are not necessarily all compatible with the lead free process.
- Component specifications for solder reflow can be very specific, and they must be compatible with lead free solder pastes. They must also be verified for the higher processing temperatures, especially the peaks & dwells above the temperature limits recommended by the component manufacturer.
- Temperature-sensitive devices must also be verified to be compatible with the higher temperatures of the lead free process. These parts include film capacitors, molded tantalum capacitors, fuses, inductors and transformers with wire coils, non-solid state relays, and LEDs.
- Moisture: With the higher temperatures, moisture that can get trapped or absorbed during assembly can cause real problems for the boards and moisture-sensitive components. In some cases, the boards can delaminate, and to prevent this the bare boards should be baked prior to assembly to excise any moisture within them.
- Cleaning: Lead free solder flux chemistries are different from regular leaded solder flux. To clean these fluxes effectively, cleaning agents specifically for the lead free process are required, which may involve different cleaning temperatures than the standard cleaning process.
To put it simply, all of the different materials and processes of PCB manufacturing will be affected to some degree by the RoHS regulations. This will require aligning the fabrication of the board, along with the components, assembly processes, and support materials in order to get the highest level of quality, performance, and reliability while maintaining RoHS compatibility.
Part of the lead free production line at VSE
RoHS Questions to Ask Your Potential PCB Contract Manufacturer
When it is time to choose a PCB CM that will build a lead free circuit board for you, you need to do your homework first. Here are some areas that you need to explore with a potential CM about their ability to deliver a high-quality RoHS compliant circuit board:
- RoHS specific assembly processes: To be compliant, a circuit board must not be processed with lead-based solder materials and chemistry. It is important therefore that the CM you use has a designated procedure to keep leaded and lead free processes separated to guarantee their purity. What kind of processes and procedures does this CM have in place for lead free manufacturing?
- Lead free materials: To be RoHS compliant, your board must be manufactured with lead free materials and chemistry. This includes solder, solder paste, and everything else needed for the process to the final cleaning agents of the circuit board. Your CM should have a fully documented system in place so that you know that RoHS compliant materials will be used.
- Documentation: In order to meet the specific RoHS requirements, you need to be able to show that your board has been built accordingly. To do this you need to make sure that your CM has a documentation system in place that will prove that the materials, chemistry, and processes used in the manufacturing of your PCBA is compliant. Does this CM have the capability?
At VSE, we have a fully set up process for manufacturing lead free circuit boards. Our lead free process is clearly separated from our standard process, and we will supply you with all of the documentation that you need to demonstrate your product’s RoHS compliance.