RoHS Circuit Board: Non-Hazardous PCB Construction

What is a RoHS Circuit Board?

The European Union adopted the RoHS 1 (Restriction of Hazardous Substances 2002/95/EC) in 2003. 

This directive paved the way for removing six toxic substances in electronic device construction.

Subsequent amendments to this directive added more materials to the list to make electrical products safer. 

And since PCBs are the heart of electrical and electronic equipment, these directives affect their manufacturing and assembly.

So let’s look at RoHS circuit boards.

What Is a RoHS Circuit Board?

RoHS directives have banned the use of several hazardous materials in electronic products.

But the toxic material that usually applies to PCBs is Lead. So when talking about RoHS circuit boards, we refer to lead-free PCBs.

Previously, Lead was critical for making solder paste or wire. The typical ones were Tin-Lead alloys with ratios like 60:40 and 63:37.

These have melting points of 188°C and 183°C, respectively.

So reflow temperatures for welding surface-mount components using Leaded solder peaked at around 235°C.

A reflow oven for assembling surface mount components

On the other hand, Lead-free solder materials, such as Tin-Silver alloys, have higher melting points. For instance, Tin-Silver in the ratio 95:5 melts at 240°C, while 96.5:3.5 melts at 220°C. So the reflow temperature is higher, peaking at around 250°C.

So from a manufacturer’s point of view, it is costlier to build Lead-free circuit boards because of these factors.

• Circuit board materials (laminates and substrates) must have a high decomposition temperature.
• You must pick and assemble components that can withstand high temperatures.
• The assembly process requires more heat (electricity)
• Rework is more challenging.

Why Use Lead-Free or RoHS-Compliant PCBs?

Why use a RoHS-compliant PCB assembly when making and purchasing it is expensive? These scenarios describe situations that favor their use.

• If you want to sell your electronics products in the EU or other countries/states/local governments with RoHS compliance requirements
• You’ve embraced and seen the need for nature-friendly production.
• Have concerns about the health issues/risks associated with Leaded-material manufacturing
• Your clients need you to meet regulatory standards when manufacturing their PCBs
• You want to promote the advancement of Lead-free alternatives due to their breakthroughs in tiny PCB fabrication.

Lead-free solder

RoHS Restricted PCB Materials

As stated earlier, the EU adopted RoHS 1 in 2003 (published in 2002).

It restricted electronics from having six hazardous materials after July 1st, 2006. These materials include the following.

• Lead (Pb)
• Mercury (Hg)
• Cadmium (Cd)
• Polybrominated Biphenyls (PBB)
• Hexavalent Chromium: (Cr VI)
• Polybrominated Diphenyl Ethers (PBDE)

The RoHS 2 (directive 2011/65/EU) replaced and revoked RoHS 1 in July 2011. But it did not list new materials or delete the ones in the previous directive.

A RoHS lead-free badge

Instead, the regulation expanded the scope of its predecessor by including more products, such as medical devices and control/monitoring instruments. Also, the changes required manufacturers and importers of RoHS-compliant products to attach CE markings on the items.

But the regulation exempted certain electrical products from the list. These include the following.

• Military industry devices
• Aerospace equipment
• Active implantable medical devices
• Large-scale fixed installations
• Non-road mobile machinery

The latest RoHS directive came about in 2015. Known as directive 2015/863 or RoHS 3, the regulation added these four hazardous substances to the list.

• Dibutyl phthalate (DPB)
• Bis(2-Ethylhexyl) phthalate (DEHP)
• Diisobutyl phthalate (DIBP)
• Benzyl butyl phthalate (BBP)

Some of the RoHS-restricted materials on the periodic table

This regulation also included certain products, such as vape pens, two-wheeled electric vehicles, and e-cigarettes.

So overall, RoHS regulations restrict ten materials. But they do not ban them entirely.

Instead, they set their acceptable limits. These limits are 0.1% or 1000 ppm for all except Cadmium. The limit for Cadmium is 0.01% or 100 ppm.

Non-compliance can lead to hefty fines as high as €30,000 per product in Germany or a 2-year prison term. 

Resources Needed for Making Circuit Boards With 1-20 Layers

Manufacturing complex multi-layer PCBs is challenging, and you need to use the following Lead-free materials to make them RoHS-compliant.

Lead-Free FR4

RoHS-compliant FR4 materials include IS410, FR4, Polyclad 370HR, and IsolaFR415 laminates. For the prepreg, you can use T-288, Td, and T-260.

A RoHS-compliant computer circuit board

Lead-Free Solder Paste/Legend Ink

The Tin-Copper alloy solder paste SN100CL is the most preferred lead-free alternative. And you can add a small amount of nickel into the mix.

Lead-Free Stencil

SAC305, a Tin-Silver-Copper alloy, is the most preferred lead-free stencil material.

Lead-Free Surface Finish

Surface finishes provide protection, physical properties, and aesthetics to the PCB.

The popular lead-free options include palladium, nickel-gold plating, and immersion silver.

Here are the properties of these surface finishes.

Factors Affecting RoHS Material Selection

Material selection is vital when manufacturing RoHS-compliant circuit boards. So you must consider these factors when selecting the substrate.

Decomposition Temperature

Abbreviated as Td, decomposition temperature is the temperature at which the chemical bonds in a substance or compound break down.

The peak temperature in Lead-free soldering assemblies is relatively high. So the FR4 material used must have a high Td.

Glass Transition Temperature

This property refers to the temperature at which a polymer material changes from solid and glassy to soft and leathery.

Lead-free FR4 materials must have a high glass transition temperature to avoid deforming during assembly.

A graph showing the glass transition temperature and decomposition temperature of an amorphous material

Coefficient of Thermal Expansion

CTE defines the rate of change of an object’s size when temperatures increase or decrease.

Since Lead-free PCB assembly requires high heat levels, the substrate material must have a low CTE to reduce expansion.

And the CTE of the different layers should match to prevent uneven extension.

Time to Delamination

Time to delamination refers to the time a circuit board’s base material takes to delaminate when subjected to high temperatures.

The property closely relates to decomposition temperature. So if the material has a high decomposition temperature, it will have a long time-to-delamination.

Moisture Absorption

The steam pressure at the higher lead-free assembly temperatures can cause delamination.

So you might notice defects in the PCB during storage, especially if the storage area has high moisture levels.

Therefore, you should pick PCB materials with low moisture absorption and store them in a controlled environment after assembly.

Benefits of Using RoHS-Compliant Circuit Boards

• Enhanced product safety: Lead, Mercury, and other RoHS-restricted materials are toxic. So RoHS compliance assures customers of getting safe electrical products.
• Reduced poisoning: With rapid technological advances, people dispose of old electronic products in landfills when they become obsolete. If they have hazardous substances, they will end up in the soil and cause contamination. And even though these electronics might undergo recycling, there is the issue of sourcing them from mines. Extracting these materials from the ground has harmful effects on the environment.

Old computers in a junkyard

• Better thermal properties: Due to the high RoHS and Lead-free soldering temperatures, Lead-free circuit boards can withstand higher temperatures, making them more durable. For instance, modern halogen-free laminates have high thermal stability of up to 300°C.

Do RoHS Circuit Boards Have a Lower Quality?

No. On the contrary, RoHS compliance tends to improve PCB quality, albeit indirectly.

The materials required to make RoHS circuit boards must have a high decomposition and glass transition temperature.

Additionally, they must have low CTE and moisture absorption properties while maintaining a long time to delamination.

These features make the circuit boards more durable. But they increase the product cost.

Wrap Up

Although expensive to fabricate and assemble, RoHS circuit boards are necessary for building electronics moving forward due to their environmental friendliness.

 Humans have had such a significant negative impact on the environment, and using these electronics is one of the ways to save our planet. 

So contact us below if you want RoHS-compliant PCBs for your project. We’ll give you the best deals and discounts.