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Electronic manufacturing industry PCB/PCBA knowledge
What exactly is RoHs circuit board

In the PCB manufacturing industry, we can see the word “RoHS” frequently. PCB and PCBA manufacturers claim that their products comply with RoHS standards. Most of you simply know that RoHS circuit board adds value to applications, but are unaware of the specific content and regulatory requirements of RoHS when PCB manufacturing. Therefore, this article will mainly cover RoHS circuit boards.

One of the most common challenges of RoHS circuit boards is assembling multi-layer PCB (1-20 layers). In addition, to ensure that RoHS circuit boards are manufactured and assembled, any part, including PCB materials, electronic components, soldering, metallurgical tools, etc., are free of harmful substances and meet RoHs standards. Finally, the finished products need to be tested for ROHS.

Table of Contents
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What does RoHS mean on electronics?

ROHS, or Restriction of Hazardous Substance. In 2002, the European Union introduced Directive 2002/95/EC banning the use of six hazardous substances, including lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ethers, with a focus on the nature-friendly production of electrical and electronic components.

The traditional PCB manufacturing industry uses many of these prohibited substances, mainly lead. Therefore, in order to produce RoHS circuit boards, manufacturers will require user-friendly and nature-friendly alternatives to banned substances. EU countries have a greater demand for ROHS circuit boards.

Why RoHS PCB is preferred?

This standard aims to reduce the environmental impact of the substances used to make PCBs and some other products. Several harmful substances-cadmium (Cd), mercury (Hg), chromium (Cr (VI), lead (Pb), Polybrominated biphenyls (PBB), Polybrominated diphenyl ethers (PBDEs) , are restricted. Affected industries include information technology, telecommunications, toys, medical devices, electrical and electronic tools, and leisure, sports and surveillance equipment.

Benefits of RoHS PCB :
● Helps reduce metal poisoning
● Improve the security of your products
● Improved thermal performance
● Pb-free PCBs have better thermal performance than leaded PCBs and can withstand temperatures from -45° to 145°.

the feature of RoHS Circuit Board

What’s the feature of RoHS circuit board?

● Lamination time
RoHS PCBs have longer lamination times than boards containing leaded components.
● Short shelf life.
Due to its high humidity sensitivity, the shelf life is shorter compared to leaded circuit boards.
● High melting temperature
Due to the use of lead-free surface treatment, a higher melting temperature is required than leaded surface treatment.
● Organic Solderable Preservatives (OSP)
Surface treatment OSP is a water-based surface treatment agent suitable for copper, which ensures better repairability of RoHS PCBs.
● Moisture-proof packaging
All lead-free surface finishes are sensitive to moisture, so components are protected by moisture-resistant packaging.

Which substances are restricted in RoHS circuit board?

There are 6 kinds of hazardous substances specified by RoHS, of which there are 4 kinds of heavy metals restricted by RoHS: cadmium (Cd), mercury (Hg), chromium (Cr (VI), lead (Pb), especially lead.
substances restricted in RoHS circuit board
● Cadmium (Cd)
Cadmium is used in battery, LEDs, paints, pigments, solar panel, detectors, equipment, plastics and phosphorescent coatings.

● Mercury (Hg)
Mercury is mainly used in the manufacture of scientific measuring instruments (such as barometers, thermometers, etc.), polyurethane materials, electronic and electrical products, switches, lamps, lighting, electrodes, thunder mercury, etc.

● Chromium (Cr(VI)
Hexavalent chromium is used in pigments, paints, corrosion protection and alloys.

● Lead (Pb)
Lead is used in metal parts, chassis, gaskets, solder, interconnects, batteries, paints, pigments, sealed glass, and cables.

● Polybrominated biphenyls (PBB)
● Polybrominated diphenyl ethers (PBDEs)
PBDE and PBB are used in a variety of applications due to their flame retardant properties.

The maximum specifications for RoHS circuit board manufacturing and assembly are:
Cadmium: 0.01% (100ppm); Lead, mercury, hexavalent chromium, polybrominated biphenyls, polybrominated diphenyl ethers: 0.1% (1000ppm).

Considerations in RoHS PCB assembly process

Material of RoHS circuit board

Material of RoHS circuit board
The raw materials that meet the ROHS standard are not simple, the original material contains 6 kinds of toxic and harmful substances can be removed, and it must also ensure that the new material meets the needs of the product and lead-free soldering process in terms of function and performance, especially the soldering of electronic components. The following RoHs-compliant materials are commonly used to make RoHs PCBs:

Isola IS410
Iteq IT-180TC
Polyclad 370HR
Isola FR415
Isola FR408
Polyclad Getek
Rogers RO4350
Isola IS620
Polyclad 621
Nelco-13SI

Surface treatments of RoHS circuit board

Surface treatments of RoHS circuit board
● Hot Air Surface Leveling
This finish, also known as HASL. HASL uses hot air to blow off excess solder on the surface of the printed board and in the holes, and the remaining solder is evenly coated on the pads, solderless lines, and surface packaging devices.

● Immersion tin
Impregnated coatings are used to create a layer of metal, resulting in flatness. Tin is the cheapest material you can get using the impregnation process, but it may not be ideal because the tin layer will immediately begin to change color.

● Immersion Silver
Using dip silver is the same as tin, but it has a longer shelf life because it does not react with copper. Besides,, PCBs should be stored properly, or they will begin to oxidize and should be placed and reflowed within 24 hours of removal from the package.

● Electroless Nickel Plating/Gold Immersion (ENIG)
ENIG is made from chemically deposited nickel and a layer of immersion gold. It has a longer shelf life (several years) and has better solderability than tin and silver.

There still have other PCB surface finish process, which can also apply in RoHS circuit board manufacturing.

Lead-free solder paste and legend ink

Lead-free solder paste is an important material for soldering electronic components, and lead-free solder paste that meets environmental ROHS standards with lead content requirements of less than 1000ppm (<0.1%) should be used.

Electronic components

With lead-free soldering, the soldering temperature is higher. The original component requirement was 180° for lead-tin solder, and the applicable temperature became 210° after using lead-free soldering.

Soldering temperature

RoHS manufacturing requires soldering temperatures at least 30°C higher than tin-lead to ensure a reliable connection between the board and the components. In addition, components and PCBs hold up much longer than tin-lead solder at this higher temperature due to the poor wettability of lead-free solder.

RoHS Circuit Boards detection method

RoHS Circuit Boards detection method

X-ray spectroscopy
Fourier spectroscopy
Spot method to measure hexavalent chromium
Gas chromatography
Liquid chromatography

Conclusion

PCB and electronic manufacturing as a very complex technology of manufacturing technology, because a large amount of water is used in the processing process, a large number of heavy metal wastewater and organic water discharge, causing environmental and human harm, complex composition and difficult treatment.

Due to the restrictions on the use of lead and other toxic substances in various countries, circuit boards are converted from normal circuit boards to RoHS circuit boards, and the traditional leaded electronic components in electronic manufacturing are also converted to lead-free ones. In the future, it is hoped that all electronics manufacturers, PCB and PCBA manufacturers can work together to comply with this standard.

FAQ

ROHS, or Restriction of Hazardous Substance. In 2002, the European Union introduced Directive 2002/95/EC banning the use of six hazardous substances, including lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ethers, with a focus on the nature-friendly production of electrical and electronic components.

● Helps reduce metal poisoning
● Improve the security of your products
● Improved thermal performance
● Pb-free PCBs have better thermal performance than leaded PCBs and can withstand temperatures from -45° to 145°.

There are 6 kinds of hazardous substances specified by RoHS, of which there are 4 kinds of heavy metals restricted by RoHS: cadmium (Cd), mercury (Hg), chromium (Cr (VI), lead (Pb), especially lead.

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