Methods and Skills to Improve the Rework Yield of Manual Bonding BGA

March 16, 2023

BGA rework industry is an industry that requires very high hands-on ability.There are two ways to repair BGA chips, namely BGA rework table and manual hot air gun welding.General factories or repair shops will choose BGA rework table, because the welding success rate is high and the operation is simple, there is basically no requirement for operators, 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 BGA repair yield by manual welding?The way to improve the rework yield of manual soldering BGA is to manually solder BGA, which is really good, because there are more and more chips packaged with BGA now.A lot of people are still more afraid of manual welding BGA, mainly because this package of chips are very expensive, the heart is not sure.In fact, only by trying more can we succeed.A few points for attention: after removing the BGA main controller, be sure to fill the tin, because there is some tin removal after removal, the main controller and the motherboard need to be repaired, you can wipe the tin paste and drag it with a soldering iron to ensure good contact; when blowing, the temperature should not be too high, about 280 is OK, the air gun should not be too close to the planting tin plate, you should shake the air gun to blow, so that the tin will not run around;The tin spot of the secondary tin planting is not necessarily uniform, and can be scraped by surgery, and the uneven place is filled with tin and then blown; after the BGA is planted, the BGA can be coated with soldering flux, and an air gun is used to blow evenly to make the solder spot on the BGA main control even;When the BGA is implanted on the motherboard, more flux should be applied, so that the melting point can be reduced, and the BGA can be connected with the solder on the motherboard along with the flux. After blowing, you can take tweezers to gently touch the edge of the BGA up and down to ensure good contact.This method can be used for small BGA chips, but for large chips such as North Bridge, the success rate is much lower.It is recommended to use Dataifeng BGA rework station for large BGA chips, which can improve the BGA rework yield.Improve the manual soldering BGA repair yield skills 1, with a new chip must ensure that the BGA chip's solder ball is full.As shown in the figure below, a large solder ball leads to a short circuit, and a small solder ball leads to a cold solder joint.So the new BGA chip is easy to solder.

If the bottom pad of the removed BGA chip is uneven, it is necessary to re-implant the solder to ensure that each solder ball is about the same size.(Tin planting = tin ball planting, which can also be operated manually) 2. The circuit board pad should be flat, as shown in the figure below. The pad on the circuit board was originally not soldered.SMT should first print a layer of solder paste with uniform thickness through the steel mesh.However, when the BGA is replaced manually, there will be residual solder on the circuit board (right figure below). If the solder is uneven, it will be the same as the uneven solder ball, which will cause short circuit or cold solder.

3. Apply a layer of flux evenly on the BGA pad of the circuit board with a proper amount of flux.And that fluidity of the solder tin is improved.Solder flux is included in the solder paste of SMT chip printing, and there is no solder flux in the solder ball of BGA chip.Therefore, some flux needs to be added manually during manual welding.4. Poke and move the new BGA chip on the pad with flux. After melting the solder with a hot air gun, gently poke the four corners of the BGA chip with tweezers, no more than 0.2mm each time.After the chip is slightly displaced, it can automatically return to its original position under the tension of the solder.This action will bring the untouched solder balls under the chip back into contact.Solder balls with a slight short circuit can also be separated with the help of flux.The success rate of BGA welding can be significantly improved.However, it should be noted that the hand must be light, move too much, the pad is misplaced, it is useless.The amount of movement cannot exceed half the pad pitch.Hardware engineers with shaky hands should use this trick with caution.

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