Over the years, safety of people and the environment has emerged as a priority for original electronic manufacturers across the world. Several restriction directives have been enacted by the governments across the world. The Restriction of Hazardous Substances or RoHS is a prominent directive enacted by the European Union countries to restrict the use of dangerous materials in the printed circuit boards, which may be harmful to users and the environment in many ways. Some of these restricted materials include lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenylether, Bis (2-Ethylhexyl) Phthalate (DEHP), Butyl Benzyl Phthalate (BBP), Dibutyl phthalate (DBP), and Di-isobutyl phthalate (DIBP). Except for Cadmium, most other materials mentioned are allowed at 0.1% of the total materials value in the circuit boards. However, the value of Cadmium is restricted to 0.01%, owing to its side effects.
What are the typical features of RoHS compliant circuit boards? This is the most obvious question after knowing the initial requirement of RoHS compliance, isn’t it?
Important Things You Must Know About RoHS-Compliant Circuit Boards
RoHS-compliant circuit boards differ from the lead versions in many ways. The following points will help you understand it better:
- They Are Coated with Lead-Free Surface Finishes: These circuit boards use lead-free solder finishes. The following are a few common ones among them:
- Lead-free HASL: This surface finish assures excellent solderability, and multiple thermal excursions. Lead-free HASL also provides a large scope for processing.
- Electroless-Nickel Immersion Gold (ENIG): This is an RoHS-compliant finish that produces a plane surface and a reliable solder joint. ENIG can easily resist various environmental storage conditions.
- Immersion Silver: It offers a planar surface than several HASL finishes, and is more affordable than ENIG. If you wish to use this surface finish for the next batch of RoHS-compliant PCBs ensure the boards are handled and stored with utmost care. This is because if they are left in open, immersion silver has a tendency to react with sulfur to produce silver sulfide.
- Lead-free Immersion White Tin: It is one of the least expensive surface coatings listed here. Lead-free immersion white tin assures excellent flatness of the coating on small components such as BGAs, fine pitch components, and so on. They provide excellent solderability after various thermal excursions.
- Organic Solderability Preservative (OSP): It is a water-based surface finish, which is well suited for copper pads. This environmentally-friendly surface finish is used to bond copper, and it is proven to produce a coplanar surface. The circuit boards using this finish assure better reparability.
- They Require High Melting Temperatures: All the lead-free surface finishes mentioned above demand high melting temperatures than their non-leaded counterparts. For instance, the tin soldering melts at 356°F, whereas a lead-free solder melts at 441°F. Components that use these surface finishes are designed to withstand high melting temperatures.
- They Have a Short Shelf Life: Although these lead-free, RoHS-compliant circuit boards may assure the safety of people and environment, they have a shorter shelf life when compared to their leaded counterparts. This is solely due to their high moisture sensitivity.
- They Are Provided in Moisture-Sensitive Packing: As mentioned before, all the lead-free surface finishes are moisture sensitive, so the components coated with them are provided in a moisture-protective package. A package may also have an expiry date printed on it. If you continue using the component past its expiration date, there are all chances of it being damaged due to the water vapor.
- They Have High Lamination Process Time: RoHS-compliant circuit boards require high lamination process times than their leaded components. However, most experienced and well-known printed circuit board fabricators have invested in advanced technology equipment that helps improve the speed of lamination, without affecting the quality and turnaround times.