All About Sustained Manufacturing of PCBs

Earlier, the PCB industry did not seem much concerned with the effects its processes had on the environment. According to eminent manufacturers like Rush PCB Inc., the industry used complicated multistep manufacturing processes relying on solvents like glycol ethers and toxic chemicals including dimethylformamide, formaldehyde, and lead.

Impact on the Environment

Traditional PCB manufacturing processes rely on high-emission and energy-intensive processes involving epoxy resin, glass fiber, copper, and water. Once the product lifecycle ends, most PCBs are a waste product.

Improper handling of these waste circuit boards further exacerbates the environmental problems while threatening human health. Incinerating to separate metals from PCBs releases toxic gases. Using acids to separate the metals creates acidified wastewater in large expanses.

During manufacturing, for instance, the PCB etching processes produce rinse waters containing high concentrations of nickel, lead, copper, tin, and chromium. These and other processes not only polluted the environment with chemical-loaded wastewater, but also poured hazardous waste into landfills. In addition, the PCB manufacturing processes exposed workers to chemicals and carcinogens, which often caused them reproductive harm.

However, over the years, manufacturers have changed these PCB manufacturing processes. Although yet to achieve truly sustainable PCB manufacturing processes, their processes are now compliant with the RoHS or Restriction of Hazardous Substances directive, and REACH or Registration, Evaluation, Authorization, and Restriction of Chemicals initiative. Therefore, most PCB manufacturers have now:

l? Abandoned the use of toxic chemicals

l? Checked their supply chains for ethical practices

l? Discovered environment-friendly alternatives for PCB components

Manufacturers now display their compliance with RoHS and REACH regulations. Compliance with these regulations has enabled them to move forward toward a more sustainable future.

The RoHS Directive

The European Union adopted the RoHS directive in 2003, and they expanded it in 2011. The directive bans the use of toxic substances in circuit boards. Most importers, distributors, and manufacturers are now globally compliant to the RoHS directive, which bans toxic materials including:

l? Cadmium

l? Mercury

l? Lead

l? Polybrominated biphenyl’s

l? Hexavalent chromium

l? Four classes of phthalates

l? Polybrominated diphenyl ethers

While eliminating the above chemicals from the PCB manufacturing processes, the RoHS directive also forbids any type of plating or finishes on electronic products using them. It also involves maintaining relevant documentation about compliance and non-compliance.

The original RoHS applies to electronic components, sub-assemblies, and the wiring connected with PCBs. Then there is RoHS 2 covering all electrical and electronic equipment, cables, and components. Furthermore, the RoHS 3 list includes additional hazardous phthalates. Manufacturers complying with the RoHS directives can apply the CE mark to their products.

The REACH Initiative

The European Union also started the REACH initiative, just like they did with RoHS. The United States also has several jurisdictions with similar restrictions on the use of hazardous chemicals.

For instance, the US EPA or the United States Environmental Protection Agency specifies complementary screening methods like the TRACI or Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts. They also specify RSEI or Risk-Screening Environmental Indicators for quantifying environmental impacts.

Compliance to RoHS regulations enables the manufacturer to restrict the use of hazardous chemicals in their final products. Compliance with the REACH initiative holds the manufacturer responsible for controlling the chemicals they use during the manufacturing processes for printed circuit boards and electrical and electronic components. Chemicals on the list of SHVC or Substances of Very High Concern include:

l? Di (2-ethylhexyl) phthalate

l? Dibutyl phthalate

l? Hexabromocyclododecane

l? Tributyltin oxide

l? Butyl benzyl phthalate

Unlike the RoHS, the REACH initiative also applies to the supply chain and manufacturers. For instance, a supplier must notify the PCB manufacturer that their bare and assembled circuit boards, components, housings, sub-assemblies, and other finished products comply with the REACH initiative.

Latest PCB Manufacturing Processes

While complying with the RoHS directives has brought them several advantages, PCB manufacturers have gone ahead and found alternatives to provide similar or even better performance and reliability.

For instance, rather than use the banned tin-lead solder, most manufacturing processes for circuit boards now use the tin-silver-copper solder. Although silver is among the hazardous materials, the tiny amount they use in the tin-silver-copper solder has negligible harmful impact on the environment.

Similar to their use of tin-silver-copper solder, board manufacturers also use polyamide polymer and silicone adhesives. These often contain tiny amounts of embedded silver flakes, offering high conductivity and tight bonding to circuit boards.

PCB manufacturers also use alternative lead-free solder technologies like solder dipping, solder ball formation, and electroplating.

Another advantage of switching to lead-free soldering is simplified layouts. Designers and manufacturers can now collaborate in achieving the miniaturization of components and tightly packed boards. They can now fabricate smaller boards that cost less.

Use of Alternative Materials

Along with complying with the RoHS directives and not using banned hazardous chemicals, PCB manufacturers are also moving away from using chemicals like dimethylformamides, formaldehydes, and glycol ethers in their production processes.

As such, many manufacturers are now migrating to P-PCBs or Paper PCBs. Using renewable materials, these environmentally friendly PCBs are made of flexible paper substrates and provide reliable functionality. They use lead-free ECAs or Electrically Conductive Adhesives to bond SMCs or Surface Mount Components to zinc or tin conductors acting as traces on the paper substrate. Fabricators transfer these traces to the paper PCB through technologies like ink jet printing, 3-D printing, or screen printing.

Paper PCBs demonstrate the same functionality as traditional circuit boards do. Their reliability, electrical conductivity, resistance loss, and multilayer capabilities are at par with the traditional boards.

Fabricating paper PCBs involves additive technologies like printing the ECA onto each substrate layer. The fabricator then cures the adhesive, aligns the circuits layer-wise, and uses pressure-sensitive adhesives to adhere one layer to the next. After punching vias through each layer, the assembler can mount SMCs on the conductors.

Although paper PCBs are still in the prototype stage, manufacturers have developed advanced paper materials that allow high-density and high-speed applications. Although not using RoHS-banned substances often results in loss of properties in regular materials, advanced paper materials improve the thermal and electrical conductivity, enhance the fire and moisture resistance, and improve the dielectric properties.

Use of Additive Processes

Rather than continue using the multistep subtractive process that dominates PCB manufacturing at present, manufacturers are turning to additive printing processes for making PCBs. They use inkjet, aerosol, and laser jet printing, conformal electronics, 3-D printing, and direct wire production processes. In contrast to subtractive processes for removing and wasting unneeded materials, additive manufacturing processes only add the needed material.

Using the additive processes, the design team can build schematics and layouts in conventional PCB design software. After ensuring their work adheres to the necessary design rules and error checking, they can manipulate their design in MCAD and ECAD environments and export the finished design to a printer to add the conducting traces on the substrate.

The advantage of additive processes is they do not require photomasks or etchants. Additionally, these processes are eminently suitable for designing complex patterns on thin substrates.

Using solid conductive inks or toners with charged particles, manufacturers do not need VOCs or Volatile Organic Compounds, and etch resists. Conductive inks with silver nanoparticles are suitable for printing on fabric, plastic, and paper substrates. With the capability of precise printing, there is little or no material waste while processing boards.

Use of 3-D Printing Processes

Manufacturers are also building electronic circuits using 3-D printing. They use a base material and conductive material for applying the circuitry. By using a suitable combination, the manufacturer can print a complete electronic circuit. They can print the board, traces, and some components as a single, continuous part. This method has the advantage of producing PCBs with varying shapes and designs that match different product requirements.

Use of Biodegradable Electronics

Manufacturers are also using polymers that function both as conductors and insulators. They are using biodegradable substrates with additive processes like transfer printing to build traces or compounds onto substrates.

Biodegradable dielectrics for PCBs and semiconductor components use high-dielectric constant fillers in a degradable polymer mix. Plant-based fibers offer desirable dielectric properties for boards, while synthetic polymers offer dielectric constants for capacitive sensors.

Conclusion

According to Rush PCB Inc., although the PCB manufacturing industry has come a long way, they have yet to reach the ultimate goal of creating an environmentally friendly manufacturing process.