People have long questioned the presence of some chemicals in our daily lives. Some of our more cautious citizens scorn fluorinated or chlorinated water because they’re afraid the government is using it for “mind control.” Conspiracy theories aside, it turns out fluorine and chlorine can have adverse health effects in certain forms and are often found in circuit boards. In response to this health risk the IEC developed a halogen free standard for PCB manufacturers, but what exactly is a halogen free PCB? Electronics contain a few specific materials that contain the highest concentrations of halogens. In order to create a “halogen free PCB,” you’ll need to replace some materials or reduce their use on your board. You’ll also need to decide exactly how free of halogens you want your circuits to be. Some replacements substances require special design considerations that you’ll need to take into account as well.
Electronic waste is often burned which can release dangerous halogens.
Halogens in PCBs
If you asked most designers where halogens are found in a PCB, it is doubtful they could tell you. Halogens are usually found in brominated flame retardants (BFRs), chlorinated solvents, and polyvinyl chloride (PVC). Halogens are obviously not dangerous in every form or concentration, and it’s unlikely that you’ve ever experienced health problems from holding a PVC pipe or drinking tap water. If you were to burn that pipe and inhale the chlorine gas that is released when the plastic breaks down, that might be a different story. This is the main problem with halogens in electronics; they can be released at the end of a PCB’s lifecycle. So where exactly are halogens found in a circuit board?
As you already know, PVC is used not only for piping, but also wire insulation, so that can be a source of halogens. Chlorinated solvents can be used to clean PCBs during the manufacturing process. BFRs are used in PCB laminates to reduce the risk of the board catching fire. Now that we’ve reviewed the main sources of halogens in circuits, what should we do about it?
Halogen Free PCBs
Like the RoHS lead free requirements, halogen free standards require CMs to use new materials and manufacturing methods. Like with any standard “halogen free” specific limits that are set by various organizations. The IEC defines halogen free as < 900 ppm of chlorine and bromine and < 1500 ppm total halogens, while the RoHS has its own limits.
Now why is “halogen free” in quotations? It’s because meeting the standard doesn’t necessarily guarantee your board has no halogens in it. For example, the IPC specifies tests for detecting halogens in PCBs, and these tests generally detect ionically bonded halogens. However, most of the halogens found in fluxes are covalently bonded so the test won’t detect them. This means that to make a truly halogen free board, you’ll need to go beyond what the standards specify.
If you’re looking for specific sources of halogens, one is TBBPA, which is a BFR commonly used in laminates. To eliminate this origin point, you’ll need to specify halogen free laminates like reactive phosphorus-based ones. Your flux and solder may also introduce halogens into your PCBs, so you’ll need to talk to your CM about possible alternatives there as well. Implementing new materials and technologies on your board can be a pain but there are a few advantages to halogen free circuits. Halogen free PCBs usually have good thermal reliability, which means they’re better suited to the higher temperature processes required for lead-free circuits. They also generally have lower dielectric constants, which is good news if you’re looking to maintain signal integrity.
Halogen Free Board Design
The advantages of halogen free boards come at a cost of increased complexity not only during manufacturing but also in design. One good example of this is with halogen free solder and flux. Halogen free varieties can sometimes vary the ratio of solder to flux and cause graping. This is where the solder combines into one large ball instead of being distributed across a connection. One way to design around this problem is to use solder mask to better define a pad. This hems in the solder paste and reduces defects.
Many new materials will have their own design quirks and you may need to communicate with the manufacturer or do some research before using them. Halogen free boards are increasing in number but are by no means common. You should also talk with your CM to see if they have the ability to build PCBs with halogen free materials.
As time goes on, we seem to be discovering that more and more of the materials we use on a daily basis can pose a health risk to us. That’s why organizations like the IEC develop standards for halogen free boards. Remember where halogens are usually found (BFRs, solvents, and insulation), so you can know what to replace if you need to go halogen free. Different standards allow different levels of halogens and may or may not detect certain kinds. You will need to do your research beforehand to know where the problem areas will be on your PCB. Once you know what materials you want to use, it’s a good idea to check with the manufacturer and your CM to identify the best path forward. You may need to tweak designs or work with your CM on some manufacturing steps to ensure your board can be completed successfully.
|Tempo's Custom PCB Manufacturing Service
When it comes to trying out new materials and technologies, your CM is a crucial part of the equation. That’s why it’s important to have a partner like Tempo Automation to assist you throughout the process. And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on CAD files or how to incorporate your design into a CAD format, contact us.