Methods and techniques to improve the repair yield of manual welding BGA

January 29, 2023

BGA repair industry is an industry that requires very high practical ability. BGA chip repair usually has two ways, namely BGA repair table and manual heat gun welding. Generally, the factory or repair shop will choose the BGA repair table, because the welding success rate is high and the operation is simple, there is basically no requirement for the operator, one-button operation, suitable for batch repair. The second kind of manual welding, manual welding has higher technical requirements, especially for large BGA chips, how to improve the repair yield of bga by manual welding?

A method to improve the repair yield of manual welding BGA

Can manually weld BGA, really good, because now the BGA package chip more and more, this can be closed. Many people are still afraid of manual welding bga, mainly this package of chips are very expensive, do not know. In fact, it takes a lot of trying to succeed. Say a few points to note: remove the BGA master, must fill tin, because after the removal of some detin, master and motherboard to fill, you can put the tin paste to take a soldering iron drag, so as to ensure good contact; When blowing, the temperature should not be too high or about 280. The air gun should not be too close to the tin plate. It should shake the air gun to blow, so that the tin point will not run away. The tin plant on the tin point is not necessarily very uniform, available surgery are scraping, there are uneven places to fill tin blow; After BGA is planted, the flux can be put on the BGA, and the air gun can be blown to smooth the welding spot on the BGA master. BGA planting on the motherboard when also want to play flux, so that can reduce the melting point, and can let BGA follow the flux and the motherboard tin point is connected, feel after blowing can take tweezers gently about the BGA edge, to ensure good contact. This works for small BGA chips, but for larger chips like Northbridge, the success rate is much lower. It is recommended to use Datafeng BGA repair table for dismantling large BGA chips, so as to improve the repair yield of BGA.

Techniques to improve the repair yield of manual welding BGA

1, with the new chip must ensure that the BGA chip tin ball is full. As shown below, a large tin ball leads to short circuit, while a small tin ball leads to virtual welding. So the new BGA chip, it's easy to solder.

If the bottom pad of the removed BGA chip is uneven, it needs to be re-tinted to make sure that each tin ball is about the same size. (Planting tin = planting tin balls, can also be done by hand)

2, the circuit board pad should be flat as shown below. The pad on the circuit board was originally without solder. SMT time to print a layer of uniform thickness of solder paste through the steel screen. However, when manually replacing BGA, there will be residual solder on the circuit board (the right picture below). If the solder is uneven, it will be the same as the tin ball, which will be short circuit or virtual welding.

There are two ways to make the pad even:

With the knife head soldering iron, scrape the pad again, uniform speed, the same strength, basically to ensure that the residual solder is the same. This is more technical. You can also use a tin absorbing wire to suck the residual solder away from the pad, so that the pad is flat. This is a little bit easier.

3. Add appropriate amount of flux

Evenly spread a layer of flux on the circuit board BGA pad. Helps to improve solder fluidity. Solder paste of SMT patch printing comes with flux, while there is no flux in the tin ball of BGA chip. Therefore, when welding by hand, you need to fill some flux by hand.

4. Poke and move

Place the new BGA chip on a pad coated with flux. After melting the solder with a heat gun, gently poke the four corners of the BGA chip with tweezers, no more than 0.2mm at a time. After the chip is slightly shifted, it automatically returns to its original position under the tension of the solder.

This action reconnects the unused tin ball under the chip. Slightly shorted tin balls can also be separated with the help of flux. It can significantly improve the success rate of BGA welding.

But it should be noted that the hand must be light, move big, the welding plate is mispositioned, it will be wasted. The movement should not exceed half of the pad spacing. Hardware engineers with shaky hands should be careful with this move.

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