PCBA Tech - smt processing lead-free soldering and PCBA processing

The introduction of lead-free smt patch assembly has always been a challenge for the first assembly, because it will face more challenges when PCB processing and rework are required. Performing PCBA repairs in a lead-free environment will have higher cost, quality details, time and repeatability issues-but due to lead-free requirements, all these issues need to be paid attention to. Because the lead-free process requires:

1. Train operators to conduct lead-free assembly, maintenance and inspection, and evaluate time and cost.

2. Lead-free solder materials are all more expensive than the traditional ones, such as lead-free wires, welding rods, and core solders.

3. The processing temperature (about 30-35 degree Celsius) of lead-free assembly requires higher accuracy and precision.

4. The lead-free process also requires the research and planning of the smt processing plant to establish the correct PCBA rework process.

PCBA rework

Jingbang Electronics believes that the best practice of PCB assembly rework is to firstly train and guide technical personnel and develop configuration files based on the characteristics of lead-free processes. The standard for rework is defined, whether standard solder or lead-free solder is required, the process starts the same-the required steps are:

1. Define and execute accurate thermal profile

2. The failed component must be removed

3. Clean up all rust or solder residues on site and prepare for new components

4. Replace the components with new solder and flux and reflow

5. Rework is thoroughly inspected

In a lead-free environment, accurate and reliable rework is more difficult because the PCBA and the components closest to the parts requiring repair must withstand multiple high temperature cycles. In order to protect the stability of the circuit board, the preheating temperature should be set not higher than the glass transition temperature of the PCB material.

The subsequent steps involved in the rework process vary depending on whether there is a lead-free requirement. The difference between standard and lead-free brings many challenges that can only be solved by introducing new or changed processes, including stricter and more accurate thermal profiles and extremely high accuracy throughout the PCBA rework process. This will avoid many costly problems caused by different heat distributions.

Analysis on lead-free soldering and repair of smt processing

Why preheat before PCBA processing

In the mass-produced PCB processing and welding environment, the importance of the temperature profile has been widely understood. Slow heating and preheating stages help to activate the flux, prevent thermal shock and improve the quality of solder joints during smt placement. However, when it comes to rework, prototyping, or PCBA first-piece proofing projects, it is easy to forget the importance of the warm-up phase, which may cause the equipment to be compromised even if it is not damaged. So, for such an important step, why is it often forgotten in the actual operation of the smt processing plant?

Reflow soldering preheating zone

What is the preheating before PCBA soldering?

When technicians and practitioners hear the words temperature curve or temperature curve, they think of smt reflow soldering. The four main temperature control zones can be easily seen along the huge length of the welding zone, which will eventually produce perfect welding joints, hope so. Each stage is carefully controlled and improved through the experience of technicians and trial and error. Each stage plays a role in promoting solder joint quality and reducing defects. But other industrial soldering machines may not have such fine temperature control. But what they have in common is the warm-up phase.