Halogens in polychlorinated bipheny

Dacă întrebați majoritatea designerilor unde sunt elementele cu halogen din a PCB sunt găsite, este îndoielnic că ți-ar spune. 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. Dacă ar fi să arzi acel tub și să inspiri gazul de clor eliberat atunci când plasticul se sparge, ar putea fi o poveste diferită. Aceasta este principala problemă cu halogenii din electronică. Ele pot fi publicate la sfârșitul ciclului de viață al 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. Solvenții clorurati pot fi utilizați pentru curățarea PCBS în timpul producției. BFR este utilizat pentru laminatele PCB pentru a reduce riscul de incendiu al plăcilor. 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. La fel ca orice limită specifică standard „fără halogeni” stabilită de diferite organizații. 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. Aceasta înseamnă că pentru a realiza o foaie cu adevărat fără halogeni, trebuie să depășiți cerințele standard.

Dacă sunteți în căutarea unei surse specifice de halogeni, una este TBBPA, care este BFR utilizat în mod obișnuit în laminate. To eliminate this starting point, you need to specify halogen-free laminates, such as active phosphorus base laminates. Fluxul și lipirea dvs. pot introduce, de asemenea, halogeni în PCB, așa că va trebui, de asemenea, să discutați cu CM ce alternative pot exista acolo. Poate fi dureros să folosești materiale și tehnologii noi pe plăci, dar circuitele fără halogeni au câteva avantaje. 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.

Design de placă fără halogeni

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 exemplu bun sunt lipiturile și fluxurile fără halogeni. Halogen-free varieties can sometimes alter the solder to flux ratio and cause scratches. Acesta este locul în care lipirea se îmbină într-o bilă mare, mai degrabă decât să fie distribuită prin îmbinare. 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. De asemenea, ar trebui să discutați cu CM pentru a vedea dacă au capacitatea de a fabrica PCBS din materiale fără halogeni.

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. Standarde diferite permit cantități diferite de halogeni, iar anumite tipuri de halogeni pot fi detectate sau nu. 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.