Latest learning: Hand soldering & wave soldering in PCB Assembly

Features of hand soldering

1. Hand soldering?is almost always difficult to control the amount of solder and soldering?angle, the consistency of soldering, and the tin penetration rate of metallized holes, especially when the pins of electronic components are gold-plated.?When soldering, the location where tin-lead soldering needs to be completed must be removed and tinned. This operation is more difficult for hand soldering.

2. As the density of PCB boards increases and the thickness of the circuit board increases, the soldering?heat capacity increases. Soldering iron soldering?is more likely to cause insufficient heat, resulting in virtual soldering or through-hole solder climbing height that does not meet the requirements. In order to forcefully achieve the required Heat, high temperature and long soldering?time are likely to cause damage to the PCB circuit board and even the pads to fall off.

3. The temperature of the soldering iron tip is difficult to accurately control. This is the most fundamental problem. If the temperature of the soldering iron tip is too low, it is easy to cause the soldering temperature to be lower than the lower limit of the process window, resulting in cold soldering or virtual soldering. At the same time, due to the limited thermal recovery of the soldering iron, it is very easy to cause poor tin penetration in the metallized through holes. If the temperature of the soldering iron tip is too high, it is easy for the soldering temperature to be higher than the upper limit of the process window and form an overly thick intermetallic compound layer, which will cause the solder joints to become brittle and reduce their strength, and may cause the pads to fall off and the circuit board to be scrapped.

4. The quality of hand soldering?joints is often affected by the operator's knowledge, skills and emotions, which is not stable.

5. The cost advantage of labor over machinery and equipment (wave soldering) is gradually being lost.

Advantages of wave soldering

1. Compared with manual soldering, wave soldering has many advantages such as good soldering?quality, high efficiency, strong flexibility, low error rate, less pollution and diversified soldering?components. The essential difference between wave soldering and manual soldering lies in the preheating area. In the preheating area, the impurities in the flux on the PCB board will be effectively volatilized, thereby improving the quality of the product's tin bath. Again, its work efficiency will be higher than that of manual soldering. It is much higher and the board surface is cleaner than manual soldering!

2. The wave soldering process has sufficient adjustment space to adjust the soldering?conditions of each solder joint (such as the amount of flux sprayed, soldering?time, soldering?wave peak height and wave peak height) to the appropriate level, and the defect rate can be greatly reduced and may even reach Zero-defect soldering of through-hole electronic components.

3. Wave soldering uses a programmable and movable small tin cylinder and various flexible and diverse soldering?nozzles. Therefore, during soldering, the program settings can be used to avoid some fixed screws and reinforcing ribs on the B side of the PCB, so as to avoid To prevent damage caused by contact with high-temperature solder, there is no need to use methods such as custom soldering trays.

Disadvantages of wave soldering

1. Different solder joints on the same circuit board may require very different soldering?parameters due to their different characteristics (such as heat capacity, pin spacing, tin penetration requirements, etc.). However, the characteristic of wave soldering is that all the solder joints on the entire circuit board are soldered under the same set parameters, so different solder joints need to "make do" with each other, which makes it difficult for wave soldering to fully meet the soldering?requirements of a high-quality circuit board.

2. The following problems are likely to occur in practical applications:

l Excessive thermal shock can easily cause the entire circuit board to deform, causing the component solder joints on the top of the circuit board to open.

l Surface-mounted devices soldered on double-sided mixed circuit boards may undergo secondary melting.

l Soldered thermal components (capacitors, LEDs, etc.) are easily damaged due to excessive temperature

l The tooling fixtures used to prevent the above situation can easily form soldering?shadows and cause cold soldering.

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3. The operating cost is high. In the actual application of wave soldering, the full-board spraying of flux and the generation of tin slag have brought high operating costs; especially in lead-free soldering, because the price of lead-free solder is more than three times that of lead solder. , the increase in operating costs caused by the generation of tin slag is staggering. In addition, lead-free solder continuously melts the copper on the pad, which will cause the composition of the solder in the tin cylinder to change over time, which requires regular addition of pure tin and expensive silver to solve.

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4. Repairing and maintenance are troublesome. The residual flux during production will remain in the wave soldering transfer system, and the generated tin slag needs to be removed regularly, which brings more complicated equipment repairing and maintenance work to the user.

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5. Poor circuit board design brings certain difficulties to production. When soldering?some circuit boards, because designers do not consider the actual production conditions, no matter what wave soldering parameters we set and various fixtures we use, the soldering?effect is always difficult to be completely satisfactory (for example, some key parts are always There are defects such as poor tin penetration or bridging). Repair soldering has to be performed after wave soldering, thereby reducing the long-term reliability of the product.