Soldering Tip: Key to Good Solder Joints

Estimated reading time: 3 minutes

For more than 85 years, JBC Soldering has been providing soldering and rework tools for the electronics manufacturing industry. Headquartered in Barcelona, Spain, the company also has branches in St. Louis, Missouri, in the USA; Guadalajara, Mexico; Hong Kong; and Shanghai, China.

In an interview with SMT Magazine at the recent NEPCON South China event in Shenzhen, Enrique Moreno, technical support engineer, discusses the key parameters to consider during hand soldering to achieve the perfect solder joint.

Stephen Las Marias: Solder joint defects are among the key problems in PCB assembly. Why do you think so?

Enrique Moreno: Mainly, the problem with hand soldering on PCBs comes with the bigger planes, and most especially with barrel filling. Good thermal transfer is important to make a good solder joint. Maybe this can be solved with high temperature on the tip, but then the intermetallic formation of the solder joint can be too big. You can have problems on the mechanical strength of the solder joint. Later, it may crack, leading to product defects.

Las Marias: What are the parameters to consider to make those perfect solder joints?

Moreno: The most important is temperature. If it is too high, the pads will burn; while too low a temperature and the tin will not melt. But also important is how this thermal transfer is done to the PCB. For this, JBC has special tips that allow users to fill those barrels easily. We also have special preheaters that can help them if they need an extra heating system while they are soldering. Users don’t need to reach a soldering temperature to 400°C to avoid this huge intermetallic part; they can control the temperature to avoid problems on the PCB.

Good tools are needed. You need a system with good soldering tips, where energy is reactive, not cumulative—imagine a big soldering tip with plenty of heat inside. Temperature and tips change. Regarding thermal transfer, the more heat that can reach the component and pin parts, the faster and easier soldering is for the operator. Also, very critical is the use of the appropriate flux because it takes oxidation off the pins and the pads.

Las Marias: What is the proper temperature to achieve good intermetallic formation?

Moreno: Good intermetallic connection needs to be achieved. The problem is that when it’s really high temperature, the intermetallic bonds increases. If you go with lower temperature, the soldering tip’s life is longer. Soldering can be done in several different temperatures, so as low a temperature you can select, will help the tip last longer. At the end, of course, it is not that big a difference between 320°C and 350°C in terms of soldering. But the tip life will last longer with 320°C than in 350°C. In this way, we recommend going as low a soldering temperature as you can. Sometimes, we know that operators are under pressure from production, so they increase the temperature to do soldering faster, but the quality and reliability will be compromised. Operators should be trained properly, and they need to be trained in soldering.

Las Marias: After hand soldering, is visual checking enough to know whether the solder joint is good or not?

Moreno: Visual checking is not enough. You cannot see whether intermetallic bonds are being formed just by looking at the solder joint. For example, if you do barrel fill, you need extra equipment such as X-ray inspection machines, where you can see if the barrels are filled or not. Sometimes you could see the top and the bottom of the solder joint, but inside, it is not a good joint.

Las Marias: What can you say about the move towards automated/robotic soldering? Do you see this trend becoming more popular in the future?

Moreno: We are quite sure that automation and robotics will increase. In line with this, JBC just developed new soldering tools for automation including a soldering head, new cartridges, features automatic tip changing, tip cleaning, and automatic fillers—all of them Industry 4.0-enabled.

Las Marias: Who will achieve the perfect solder joint: a robotic soldering system or a highly skilled operator?

Moreno: First, someone needs to tell the robot how to do it. If you don’t know how to program this robot to make the perfect solder joint, you are lost. Robots are quite good for repetitive tasks, like in a production environment. But good operators with really good skills can also work in rework environments, where several different tasks need to be done. He can choose the appropriate temperature, appropriate tools, just by looking at the PCB.

Las Marias: Thank you very much, Enrique.

Moreno: Thank you.