What Is Halogen Free PCB?
Halogen Free PCBs are those printed circuit boards are manufactured with halogen-free PCB materials with halogen-free methods, and meet the relative standards. Like the RoHS lead free requirements, halogen free standards require contract manufacturers (CMs) to use new materials and manufacturing methods. Like with any standard “halogen free” specific limits are set by various organizations. The IEC defines halogen free as <900ppm of chlorine and bromine and <1500ppm 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 circuit 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.
Halogen Free Board Advantages
Implementing new materials and technologies on your board can be a pain but there are a few advantages to halogen-free circuit boards. Halogen free boards usually have good thermal reliability, which means they’re better suited to the higher temperature processes required for lead-free printed circuit boards (PCBs). They also generally have lower dielectric constants, which is good news if you’re looking to maintain signal integrity.
Halogen Free PCB Design
The advantages of halogen free boards come at a cost of increased complexity not only during PCB 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 PCB manufacturer 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.
Then 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 MADPCB to assist you throughout the process. And to help you get started on the best path, we furnish information for your DFM checks.