PCB News - In the PCB industry, tin-lead solder is the key material

In the PCB industry, PCB tin-lead solder is a very important material. However, due to the implementation of China's "Administrative Measures for the Control of Pollution by Electronic Information Products" and related environmental protection laws and regulations, materials or processes containing six hazardous substances such as lead will be banned, and tin-lead solders will be gradually used due to the high content of lead. Prohibited to use.

"Lead-free solder-chemical composition and form" is the most basic material standard for lead-free, which includes 23 alloy solders, covering the most common tin-silver, tin-copper, tin-silver-copper, tin-zinc, tin-bismuth, Commonly used alloys such as tin antimony series. But it should be noted that some of these alloys have patent rights. The "Flux for Lead-Free Soldering" stipulates the marking, classification, specifications, test methods, performance and reliability indicators of the flux materials used for lead-free solders. Among them, the flux is improved according to the characteristics of the lead-free process. Performance evaluation and testing methods. The "Tin Alloy Powder for Electronic Soldering" standard specifies the technical requirements and test methods of solder powder based on the requirements of lead-free SMT (surface mount) solder paste. Strictly speaking, solder powder is just a different form of powder solder in the solder, and it is incorporated into the basic solder standard in foreign standards and is not separately formulated. The "General Technical Requirements for Solder Paste" standard has been revised on the basis of the original standard for the characteristics of lead-free.

The content includes lead and lead-free parts. It mainly stipulates the logo, specifications and technical requirements, test methods, etc. of solder paste. The "Test Methods for Lead-Free Solder" standard specifies 8 test methods, including melting point test, expansion rate test, wettability test, mechanical property test, solder joint tensile and shear strength test, QFP solder joint 45 Degree angle tensile strength test, chip component solder joint shear test, lead-free oxidation resistance evaluation, etc.

The implementation of PCB lead-free involves solder, flux, PCB (printed circuit board), components, equipment and technology, quality and reliability and many other links. If there is no unified technical standard, it will inevitably lead to the cost of the entire PCB industry. An increase will also cause confusion in the convergence of the industrial chain.

In order to cooperate with the implementation of China RoHS, when the former Ministry of Information Industry established the "Electronic Information Product Pollution Control Standards Working Group", the industry established 3 "Limits and Testing", "Marking and Certification" and "Lead-Free Soldering". Standard drafting group. There are 5 standards to be drafted in the first batch of projects, namely "Lead-free Solder-Chemical Composition and Morphology", "General Technical Requirements for Solder Paste", "Flux for Lead-Free Soldering", and "Tin Alloy Powder for Electronic Soldering" Compatible with "Lead-free Solder Test Method" (including melting temperature, mechanical stretching, expansion, wettability, solder joint stretching and shearing, QFP (small square flat package) lead solder joint 45 degree stretching, chip component soldering 8 test methods for lead-free solder or solder joints, including point shearing and dynamic solder slag test methods). The lead-free soldering standard has not been issued since it was drafted in 2004. The main reasons are two aspects: First, many mainstream lead-free solders listed in the standard are protected by patents. If they are written rashly Standards may bring risks to users; second, there has been a lack of coordination and organic connection between the five standards undertaken by different units. If they are issued, it will inevitably cause troubles and inconvenience to the industry. After everyone’s joint efforts and negotiation, the current standard has been basically completed and passed the review of the expert review committee, and has been announced to the industry.

In the PCB manufacturing industry, from materials to components to components to complete equipment, the upstream and downstream are closely related, and the most critical link in the process of converting to lead-free is the process of making PCB circuit boards into components. In this link, lead-free solder brings three difficulties. One is that the melting point temperature rises, which will cause thermal damage; the other is that the heat resistance of the parts causes the process window to be very small, and improper process control results in product quality. Will decline; third, the low wettability of the material will reduce the quality of lead-free materials.