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Pad fall off after PCB assembly

Time:2021-05-18 15:08

Recently, our JY company produced a batch of swimming pool PCBA products for an Australian customer, called Chlorine Boards.
During our later inspection, the pad falling off occurred when the electrolytic capacitor on the board was gently touched by hand. Therefore, we recommend that customers update the PCB design in the next batch of orders and increase the width of all electrolytic capacitor pad rings to avoid the problem of pad falling off.
So in this issue of the article, I will introduce to you the problem of pad falling off.
First of all, let's understand the main reason for the pad falling off.

Analysis of the reason why the pad is easy to fall off when the circuit board is soldered
During the use of the circuit board, the pads often fall off, especially when the circuit board is reworked. When using an electric soldering iron, the pads are very easy to fall off. The circuit board factory has made some suggestions on the reasons for the fall off of the pads in this article. Analyze and take corresponding countermeasures for the reasons.
When the circuit board is soldered, the pad is easy to fall off. Analysis:
1. Board quality problems. Due to the poor adhesion of the resin glue between the copper foil of the copper clad sheet and the epoxy resin, even the large area copper foil of the circuit board copper foil is very easy to interact with the epoxy resin under the slight heat or mechanical external force. The separation leads to problems such as peeling of the pad and peeling of the copper foil.
2. The influence of circuit board storage conditions. Affected by the weather or stored in a damp place for a long time, the circuit board absorbs moisture too high. In order to achieve the ideal welding effect, it is necessary to compensate for the heat taken away due to the volatilization of moisture during the patch welding. The welding temperature and time must be extend. Such soldering conditions are likely to cause delamination between the copper foil of the circuit board and the epoxy resin.
3. Electric soldering iron welding problem, the adhesion of general circuit boards can meet ordinary soldering, and there will be no pad falling off. However, electronic products are generally likely to be repaired. Rework is usually repaired by soldering with an electric soldering iron. Due to the local high temperature of the electric soldering iron It often reaches a temperature of 300-400 degrees, which causes the local temperature of the pad to be too high, and the resin glue under the copper foil of the pad falls off due to high temperature, and the pad falls off. When the soldering iron is disassembled, it is easy to attach the physical force of the soldering iron tip to the pad, which is also the cause of the pad falling off.
The main reasons that JY Company summarized in the actual PCBA processing process above.
So, next we must discuss the remedy of the pad falling off.
There is no way to recover the pad falling off, and the flying line is the solution.
Normally, the electrical connection should be completed through the copper on the PCB. Now that the pad falls off, the two unconnected circuits must be connected with wires.
But generally speaking, a good remedial effect can be achieved by following the steps below:
Material: a very thin copper wire, preferably an enameled wire, if not, take a thin wire blade from the ordinary wire. A thin blade will do, mainly for scraping green oil.
1 Scrape off the green oil on the trace connected to that pad. The location of this selection is very important. Don't be too close to the pad, which is not good for wire bonding.
2 Solder that component and ignore the missing pad.
3 Use a wire to directly connect the scraped area to the pin of the component.
In addition, the following two points can also prevent the pad falling off.
1 The circuit board is vacuum packed before leaving the factory, and desiccant is placed to keep the circuit board in a dry state. Create conditions to reduce false welding and improve weldability.
2  In view of the thermal impact of the soldering iron on the pad during rework, we try to increase the thickness of the copper foil of the pad through electroplating, so that when the soldering iron heats the pad, the thermal conductivity of the thick copper pad is significantly enhanced and effective The lower the local high temperature of the pad, and the fast heat conduction makes the pad easier to remove. To achieve the solder resistance of the pad.
The above is the sharing of this article of JY Electronics. If it can bring you some help, I will be very honored.

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