- Lead
- Mercury
- Cadmium
- Hexavalent Chromium
- Polybrominated Biphenyl
- Polybrominated Diphenyl
- FR370HR
- IS410
- Polyclad370HR
- IsolaFR415
- T-260
- Td
- T-288
- Tin
- Silver
- Copper
- Nickel
- Bismuth
- Zinc
- Antimony
- Strong joint formation
- Melts at lower temperature
- Good electrical conductivity
- Ease of use
- Fewer quality problems
- Strong wetting
- Longer shelf life
- High toxicity
- Environmentally friendly
- Non-hazardous to human health
- Good quality of soldering
- Higher melting point
RoHS compliant PCBs are common in the PCB industry. RoHS is an acronym for Restriction of Hazardous Substances, and it is a directive from the European Union, which they introduced as 2002/95/EC, in the year 2002. The directive prohibits the use of six hazardous substances, such as:
The objective of the directive is to focus on the environment-friendly production of components for the electrical and electronic industry. Therefore, for circuit board manufacturers in the USA and elsewhere, making RoHS compliant PCBs means using environment-friendly alternatives for the substances prohibited by the directive. As the demand for RoHS compliant PCB boards increases in the countries belonging to the European Union, circuit board manufacturers supplying to these countries must adhere to the directive.
With rapid replacement of electronic devices, most discarded electronics is ending up in landfills. Hazardous substances like lead, present in conventional PCBs, pose a grave threat to the environment. This is the basic cause for concern that the RoHS directive has set out to address. Most organizations are now preparing to avoid the use of hazardous substances by opting for the RoHS compliance.
Why Opt for Lead-Free PCBs?
There are several reasons that indicate opting for lead-free PCB board is advantageous:
Lead is Harmful to Humans: People manufacturing printed circuit boards must necessarily be in direct contact with solder. As solder contains lead, it enters the human body through eyes, nose, and mouth, as solder fumes. Presence of lead in the human body is hazardous to health, and as a safety precaution, safer products must replace lead.
Lead is Harmful to the Environment: As about 4% of landfill waste consists of electronics, the presence of lead therein has a very wide effect on the environment. At present, many thousands of tons of lead-based electronic products occupy landfills. The presence of acidic rainfall further aggravates the situation by leaching the lead from the electronics into the soil. This contaminates not only the soil, but also the groundwater system that irrigates our crops, and ultimately reaches us.
RoHS Compliance Leads to Lead-Free PCBs: Industries opting for RoHS compliance must use lead-free PCBs for their RoHS compliant products.
With increasing use of electronic products in our lives, it is essential that we protect ourselves from hazardous substances threatening our lives. Therefore, all electronic PCB manufacturers must comply with the RoHS directives to save the environment.
Essential Resources for Manufacturing RoHS Compliant 1-20 Layer PCBs
PCB manufacturers consider manufacturing boards up to 4 layers as convenient. However, with the progress of technology, 20-layer boards are now common, but their design and manufacturing is more complicated. As PCB manufacturers prefer a process with a layer-focus for fabricating boards, making 6+ layer boards falls under a category that the manufacturers call complex multilayer PCBs. The design of these complex multilayer boards can encompass various criteria.
In complying with the RoHS directive, the PCB board designer must consider multiple factors when designing boards. This is apart from the basic requirement that the PCB material must not absorb moisture, and the absence of lead must not lead to a loss of soldering strength. Essentially, the resources necessary for manufacturing RoHS compliant 1-20 layer printed circuit boards includes:
RoHS Compliant PCB Material: Manufacturers must use RoHS compliant PCB materials when fabricating printed circuit boards.
Some popular substrate/laminate materials include:
Some important characteristics of lead-free materials used in the preparation of laminates and prepreg include:
RoHS Compliant Solder Paste: Also known as lead-free solder material, it typically consists of lead-free solder and flux. Commercial lead-free solder can have various compositions or % weight of metals like Tin (the main element), and Silver, Copper, Antimony, Cobalt, Bismuth, Nickel, Zinc, Indium, Germanium, and other rare-earth elements. The actual composition decides the properties of the solder paste.
For instance, solder paste SAC305 with 96.5% Tin, 3% Silver, 0.5% Copper, offers high strength and thermal fatigue. Although it has a low melting point, it is not eutectic, and rapidly attacks stainless steel in stencils.
Solder paste SN100C with 99.3% Tin, 0.7% Copper, 0.06% Nickel, and 0.005% Germanium, is eutectic with a well-defined melting point.
RoHS Compliant Stencils: It is important that manufacturers use stencils made of material that does not contain any of the six hazardous substances that the RoHS directive prohibits.
RoHS Compliant Surface Finish: Board manufacturers add surface finish to their PCBs for improving their aesthetic value and enhance their shelf-life and soldering capabilities.
Many board manufacturers prefer using SN100CL as lead-free HASL surface finish. SN100CL consists of 99.3% Sn, 0.6% Cu, and a small amount of Ni. The major advantage of using SN100CL is it provides a highly uniform and flat surface, and superior wetting that enables very fine-pitch soldering.
RoHS Compliant Soldermask and Legend Inks: Board manufacturers must use RoHS compliant solder mask and legend inks for solder mask and legend printing on their boards.
Experienced PCB manufacturers typically use the above resources for making RoHS compliant complex multilayer printed circuit boards.
Differences between Leaded Solder and Lead-Free Solder
Leaded solder essentially consists of lead and tin as the major ingredients. That is why it is also known as SnPb solder. However, increasingly, the occupational risk of lead is coming to the fore. Dust and fumes associated with lead soldering have been proven to be toxic when inhaled. All this has made lead solder a documented health hazard.
Solder without lead, or lead-free solder, has now come to replace conventional leaded solder. Lead-free solder comprises many substances, in varying proportions, like:
Major components of some common lead-free solders are:
Tin-Silver: The silver increases the electrical conductivity, while also acting as a catalyst. The presence of tin improves the mechanical strength of the solder, while also acting as a protective agent and reducing corrosion possibilities.
Tin-Copper: Presence of copper increases the mechanical strength and the electrical conductivity
Tin-Zinc: Presence of zinc helps lower the melting point of the solder.
Advantages and Disadvantages of Leaded Solder
Leaded solder offers several advantages:
Disadvantages of lead solder:
Advantages and Disadvantages of Lead-Free Solder
Advantages of lead-free solder:
Disadvantages of lead-free solder:
Although leaded solder joints look more shiny and clean, and lead-free solder looks rather gray and dull, this is more due to slower wetting in lead-free solder on PCB boards. However, manufacturers using lead-free solder find it to offer better PCB soldering. As lead-free solder does not spread during reflow, it results in better soldering joints. Moreover, lead-free soldering does not lead to the rapid stencil wear that comes from leaded solder use. Use of lead-free solder results in more reliable solder joints as compared to those from leaded solder joints.
Conclusion
In electronic products, reliability is a major issue. Solder joints must be reliable, and they must not act as heat intermediaries. To ensure reliability of solder joints it is necessary to consider the type of solder that works best with the application on hand, while considering factors such as ease of use, wiring requirements, cost, and safety. A reliable circuit board manufacturer can provide RoHS compliant printed circuit boards without sacrificing quality or the time to market.
