Lead Free – What Changes Do I Make To My Raw PCB?
Joe Herz, Senior Manufacturing Engineer

With the European Union RoHS and WEEE directives looming, many companies are faced with questions such as; “Is our product designed to allow easy conversion to a Lead-Free process?” And “What changes will we need to make to meet the requirements?” From a manufacturing process standpoint, there are several key areas that require a knowledge base to make decisions from. This article is intended to provide some insight into what facts need to be considered in designing or converting to a lead-free compatible raw PCB.

PCB Laminates Are Not Created Equal

Soldering with lead free alloys requires higher process temperatures. Reflow soldering with standard 63/37 SnPb (melting point of 183C) can be accomplished with peak temperatures of 215C. Lead free alloys will require peak temperatures of 230-245C. Standard FR4 laminates with glass transition temperatures (Tg) of 140C are not suited for lead free processing. Even FR4s with Tg of >160C are not necessarily the answer. The decomposition temperature and Coefficient of Thermal Expansion (CTE) are parameters that need to be considered when selecting a laminate system for lead free processing. Several phenolically cured resin systems are now available as a suitable match for many lead free applications. Isola IS410 and MEM 1755 are two materials that have been qualified for use in lead-free processing.

PCB Surface Finishes

By far, the most popular PCB finish today, is tin/lead HASL (Hot Air Solder Level). As with any finish, the goal is to protect underlying copper from oxidizing and provide a solderable surface. Obviously, a tin/lead HASL finish is not compatible with a lead free process. The alternatives to tin/lead HASL are numerous but not all are suitable for a given application. Some of the choices include: Electrolytic tin, electroless tin, immersion silver, electroless nickel/immersion gold (ENIG), and organic solderability preservatives (OSPs). Many have chosen an ENIG finish as it is a proven process, provides good solderability and very flat pad/land surfaces for high density packaging such as BGAs and fine pitch leaded devices.

The good news for designers is that a change to a compliant laminate and surface finish is fairly seamless. In most cases, only a change to a fabrication drawing with updated laminate and finish callouts is needed. Rarely will a redesign be necessary.

For additional information on the material above, please contact Controltek’s Manufacturing Engineering department.