Should You Use Lead-Free PCB Assembly?
In February 2003, EU 1, which includes nearly 30 of the continent’s 50 countries, adopted the Restriction of Hazardous Substances Directive 2002/95/EC, or RoHS 1. The directive set July 1, 2006 as the deadline for restricting the use of six “hazardous materials” in the manufacture of electrical and electronic equipment. Compliance with the directive and its subsequent amendments (which added four additional substances) became mandatory for European manufacturers and all other countries producing electronics for the EU market.
Since PCBs are a major component in virtually all electronic systems, the RoHS directive applies directly to many PCB manufacturing steps. By far the most impacted stage of board manufacturing is PCB assembly (or PCBA), and RoHS compliance means replacing traditional lead-based solder with lead-free alternatives. But what does this mean for your PCB development? Before we tackle that question, let’s take a look at lead-free and lead-free board assembly. Then, you’ll be in a better position to decide whether you should use lead-free PCB assembly.
Leaded vs. Lead-Free PCB Assembly
When assembling a circuit board, the components, either surface mount technology (SMT) or through-hole, are connected via a soldering process. For decades, most solders used for PCBA have been tin-lead (Sn-Pb) alloys. Popular Sn-Pb ratios are 60/40 and 63/37, which have melting point temperatures of 188°C (370°F) and 183°C (361°F), respectively. During reflow, which is the preferred method for connecting surface mount device (SMD) packages, the solder can reach temperatures as high as 235°C (455°F) before cooling as it turns to liquid form.
The temperatures for lead-free PCBA are generally higher than those for Sn-Pb solder. For example, the melting point temperatures for tin-silver (Sn-Ag) are 220°C (428°F) for 96.5/3.5 and 240°C (464°F) for 95/5, respectively. Reflow temperatures may peak at 250°C (482°F). These higher temperatures have implications for board construction and component selection. If the board material chosen has too low a decomposition temperature, exposure to the high temperatures involved in lead-free PCB assembly may cause irreversible damage. Care must also be taken when selecting components to ensure that there is no damage, especially during reflow if high temperatures are present on the board for an extended period of time.
From a PCB manufacturing perspective, the main concern with lead-free PCB assembly is damage to the board caused by elevated temperatures. Rework is also more difficult. Materials are another consideration, as substrates and laminates must be selected based on their temperature properties. However, before deciding too early that choosing lead-free PCB assembly is unreasonable, let’s explore other reasons to make this change.
You should use lead-free PCB assembly if:
If any of the items in the following list describe your situation, you may benefit from using lead-free PCB components.
l Your product may be sold in a country with regulatory requirements, such as the European Union.
l Your state or local government requires lead-free manufacturing processes, such as in California.
l The OEM of the motherboard requires you to meet regulatory standards, such as IBM and Hewlett Packard.
l You are concerned about the health risks to people who use and consume lead-based products.
l You are concerned about the potential liability risks associated with lead-containing products.
l You understand the breakthroughs that lead-free PCB assembly has made in smaller PCB manufacturing and want to promote continued progress in this area.
l You recognize the drive for green manufacturing and want to attract customers who place a high premium on these issues.
Today, in order to comply with the RoHS directive, the following substances can only be present at the levels shown.
Ensuring that your boards are RoHS compliant means that you must ensure that your selected contract manufacturer (CM) has defined lead-free processes, including soldering, materials, components, solder mask, and surface finish. Lead-free PCB assembly is quickly becoming the standard for PCB manufacturing. As mentioned above, this is due to regulatory requirements, environmental concerns, and other reasons.