Halogens in polychlorinated bipheny

If you ask most designers where the halogen elements in a PCB se encuentran, es dudoso que te lo digan. Halogens are commonly found in brominated flame retardants (BFR), chlorinated solvents and polyvinyl chloride (PVC). Halogens are clearly not dangerous in every form or concentration, and there are no health problems with holding PVC pipes or drinking tap water. Si quemara ese tubo e inhalara el gas de cloro que se libera cuando el plástico se rompe, esa podría ser una historia diferente. Este es el principal problema de los halógenos en la electrónica. Pueden publicarse al final del ciclo de vida de los PCB. So, where exactly do you find halogens in the circuit board?

As you know, PVC is not only used for piping, but also for wire insulation, and therefore may be a source of halogens. Se pueden utilizar disolventes clorados para limpiar PCBS durante la fabricación. El BFR se utiliza en laminados de PCB para reducir el riesgo de incendio en la placa. Now that we have examined the main source of halogens in the circuit, what should we do about it?

Halogen free PCB

Like RoHS lead-free requirements, halogen-free standards require CM to use new materials and manufacturing methods. Como cualquier límite específico estándar “libre de halógenos” establecido por varias organizaciones. The IEC definition of halogens does not contain chlorine and bromine less than 900 PPM and total halogens less than 1500 PPM, while RoHS has its own limitations.

Now why quote “halogen-free”? This is because meeting the standards does not necessarily guarantee that your board is halogen-free. For example, IPC prescribes tests for detecting halogens in PCBS, which typically detect ionic bonded halogens. However, most of the halogens found in the flux are covalently bound, so the test cannot detect them. Esto significa que para hacer una lámina verdaderamente libre de halógenos, debe ir más allá de los requisitos estándar.

Si está buscando una fuente específica de halógenos, una es TBBPA, que es el BFR que se usa comúnmente en laminados. To eliminate this starting point, you need to specify halogen-free laminates, such as active phosphorus base laminates. Su fundente y soldadura también pueden introducir halógenos en la PCB, por lo que también deberá discutir con CM qué alternativas pueden existir allí. Puede resultar doloroso utilizar nuevos materiales y tecnologías en placas, pero los circuitos sin halógenos tienen algunas ventajas. Halogen-free PCBS generally have good heat-dissipation reliability, which means they are better suited for the high-temperature processes required for lead-free circuits. They also usually have lower permittivity if you want to preserve signal integrity.

Diseño de placa libre de halógenos

The advantages of halogen-free boards come at the cost of increased complexity not only in the manufacturing process but also in the design. Un buen ejemplo son las soldaduras y fundentes sin halógenos. Halogen-free varieties can sometimes alter the solder to flux ratio and cause scratches. Aquí es donde la soldadura se fusiona en una bola grande en lugar de distribuirse por toda la unión. One way to solve this problem is to better define the pad with a blocking film. This will edge up the solder paste and reduce defects.

Many new materials have their own design quirks, and you may need to contact the manufacturer or do some research before using them. Halogen-free boards are on the rise, but by no means universal. También debe hablar con su CM para ver si tiene la capacidad de fabricar PCBS a partir de materiales libres de halógenos.

As time goes by, we seem to find that the more and more materials we use every day pose health risks to us. That’s why organizations like IEC develop halogen-free board standards. Remember where halogens are usually found (BFR, solvent, and insulation), so if you need halogen-free, you know which halogens to replace. Los diferentes estándares permiten diferentes cantidades de halógenos y ciertos tipos de halógenos pueden detectarse o no. You need to do research beforehand to understand the location of problem areas on the PCB. Once you know which material to use, it is best to check with the manufacturer and CM to determine the best way forward. You may need to adjust the design or work with CM on certain manufacturing steps to ensure that your board is successfully completed.