Aug 20, 2020|General

Halogen Free PCBs: A Brief Introduction

If you heard the term “halogen free PCB” and want to learn more, you’re in the right place. We share the backstory behind this type of printed circuit board. 

Find out the facts on halogens in PCBs, halogens in general, and the requirements for the term halogen free. We also delve into the pros of going halogen free.

What is a Halogen Free PCB?

To qualify as a halogen free PCB, a circuit board must not contain more than a certain quantity of halogens, which is measured in parts per million (ppm). 

Halogens in PCBs

Halogens have several uses where it concerns PCBs. 

Chlorine acts as a flame retardant or as a protective coating for polyvinyl chloride (PVC) wires. It’s also used as a solvent for semiconductor development or cleaning computer chips.

Bromine can serve as either a flame retardant to protect electric parts, or to sterilize components.

What Levels are Considered Halogen Free?

The International Electrochemical Commission (IEC) sets the standard as 1,500 ppm of total halogens through the Restriction Use of Halogen. Chlorine and brome limits are 900 ppm apiece. 

If you go by the Restriction of Hazardous Substances (RoHS), the ppm limits are identical.

Be warned that there are various halogen presence standards on the market. Since halogen free manufacturing is not a legal demand, allowable levels set by independent entities (e.g., manufacturers) can vary. 

Halogen Free Board Design 

At this point, we should note that a true halogen free PCB is hard to find. There can be finite traces of halogens within your circuit board, and these compounds can lurk in unexpected places.

Let’s detail a few examples. Green circuit boards are not halogen-free unless the green substrates get removed from the solder mask.

Epoxy resins, which help protect PCBs, can contain chlorine. Halogens may also be concealed in components such as glass sizes, wetting and curing agents, and resin accelerators.

You should also be aware of the potential pitfalls using halogen free materials. For instance, without halogen, the ratio of solder to flux can be affected, causing graping. 

Bear in mind that issues like this aren’t necessarily impossible to overcome. A simple fix to avoid graping is to define pads using a solder resist, also known as a solder mask. 

It’s important to work with a reputable PCB manufacturer to ensure transparency about the halogen levels in your PCB. Although they are gaining recognition, not every manufacturer is currently equipped to produce these circuit boards. 

Nonetheless, now that you know where halogens appear and what purposes they serve, you can specify your requirements. You may need to collaborate closely with your manufacturer to determine the best course of action for avoiding unwanted halogens. 

Even though achieving a 100-percent halogen free PCB might be challenging, you can still create one with acceptable levels per IEC and RoHS regulations. 

What is Halogen?

Halogen is not a chemical or substance in and of itself. The term, which translates from Greek as “salt producer,” refers to a family of related elements on the periodic table. 

These include chlorine, bromine, iodine, fluorine, and astatine—some of which you’re likely familiar with. Fun fact: combined with sodium, halogens produce table salt! Aside from that, each element has distinct properties that make it useful to us. 

Iodine is a common disinfectant. Fluorine compounds such as fluoride are added to public water systems to promote tooth health, and they’re also in lubricants and refrigerants. 

Astatine is exceptionally rare, and not much is understood about its properties, and tennessine is still under research.

Chlorine and bromine exist in various everyday items, from water sterilizers to insecticides and—of course—PCBs.

Why Were Halogen Free PCBs Created?

Although halogens play essential roles in PCB construction, they have one drawback that’s hard to overlook: toxicity. Yes, these substances are functional flame retardants and sterilization agents, but they come at a high cost. 

Chlorine and bromine are the main culprits here. Exposure to either of these chemicals can provoke unpleasant symptoms like nausea, coughing, skin irritation, and blurry vision.

Dangerous exposure isn’t likely to occur through handling a PCB that contains halogens. Still, if the PCB catches fire and emits fumes, you can anticipate these adverse side effects.

If chlorine-containing components happen to mix with hydrocarbons, the result is dioxin, a lethal carcinogen. Unfortunately, certain countries tend to practice poor disposal due to limited resources to recycle PCBs safely. 

For this reason, improper disposal of PCBs containing high quantities of chlorine is dangerous for the ecosystem. Burning these gadgets to get rid of them—which does happen—can release dioxin into the environment.

Benefits of Using Halogen Free PCBs

Now that you know the facts, why use halogen free PCB? 

The primary advantage is that they’re a less toxic alternative to their halogen-packed counterparts. Prioritizing the safety of you, your technicians, and the individuals who will dispose of the circuit board is sufficient to consider using one. 

Additionally, the environmental risks are far lower than with units that contain significant quantities of these dangerous chemicals. Particularly in regions where best PCB recycling practices are inaccessible, lower halogen levels make for safer disposal.

In a booming tech era where consumers are increasingly conscious of toxins in their products, the applications are nearly limitless—automotive electronics, cell phones, and other devices that we keep in close contact should ideally be halogen free. 

However, lowered toxicity isn’t the only upside: they have performance benefits as well. These PCBs can usually withstand high temperatures, which makes them ideal for lead-free circuits. Since lead is another compound most industries are trying to avoid, you can kill two birds with one stone. 

Halogen-free PCB insulation can be low-cost and effective for single-use electronics. Lastly, signal integrity is easier to maintain due to the low dielectric constant these circuit boards deliver. 

We should all strive to be more conscious about limiting avoidable hazards in vital equipment such as PCBs. Although halogen free PCBs are not yet mandated by law, efforts are being made on behalf of concerned organizations to phase out the use of these harmful compounds.

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