4-layer rigid flex circuit board

In previous articles, I discussed "How to Choose PCB Materials," "A Brief Overview of PCB Materials," and "How to Prepare PCB Materials." Today, let's talk about halogen-free FR-4 materials. What is halogen-free FR-4 material? As defined by IPC and IEC, a material can only be considered halogen-free FR-4 if the content of bromine and chlorine is each less than 900 PPM, and the total content of bromine and chlorine is less than 1500 PPM. At the same time, when using halogen-free FR-4, all materials used must meet the halogen-free requirements. Halogen-free FR-4 vs. Lead-free FR-4 The grade of halogen-free FR-4 is higher than that of lead-free FR-4. Halogen-free FR-4 essentially meets the requirements for lead-free assembly. On the other hand, lead-free FR-4 that meets the requirements for lead-free assembly does not necessarily meet the halogen-free requirements. As you know, there are many types of PCB materials. Choosing the right material affects the durability and reliability of the final product.

Regarding wire bonding, ENEPIG can be considered as the initial option. ENEPIG is regarded as one of the most stable surface finishes for wire bonding, but its production cost is significantly higher compared to other surface finishes. Here, there is a solution to use ENIG with an increased gold thickness of 5u" instead of ENEPIG. Below are the conditions and results of tensile tests demonstrating the performance of ENEPIG and ENIG. Test Conditions: Using T1.0 mil gold wire, the tensile strength should be above 3 grams force (in accordance with TM-650 2.4.42.3). PCB A has an ENEPIG finish with Ni: 200u", Pd: 2u", Au: 2u". PCB B has an ENIG finish with Ni: 200u", Au: 5u". Results: PCB A: 5.091 ~ 11.186 (g) PCB B: 4.432 ~ 12.030 (g) In summary, it can be concluded that both ENEPIG and ENIG are suitable for wire bonding.