1. Adjust the position
When BGA conducts chip welding, the position needs to be adjusted to ensure that the chip is located between the upper and lower air outlets.Clamp the PCB on both ends with a clamp and fix the motherboard by hand without shaking or touching the motherboard.
2.Adjust the preheating temperature.
Before BGA welding, the main board should be fully preheated, which can effectively ensure that the main board will not deform during the heating process, and can provide temperature compensation for the subsequent heating.
The preheating temperature should be adjusted flexibly according to room temperature and PCB thickness.For example, when room temperature is low in winter, the preheating temperature can be increased appropriately, and the preheating temperature should be decreased correspondingly in summer.
If the PCB is relatively thin, the preheating temperature should be increased appropriately.The specific temperature depends on the BGA repair table.
3.Adjust welding curve.
General method of adjustment: find a PCB with a flat unformed motherboard and use the soldering pad for curve welding.After completing the fourth curve, insert the temperature measuring line of the welding table between the chip and the PCB.
The temperature.
The ideal for lead free is 217 degrees, and lead is 183 degrees.
These two temperatures are the theoretical melting points of the above two kinds of balls, but at this time the balls under the chip are not completely melted.From the maintenance corner, the ideal temperature is about 235 degrees lead-free and about 200 degrees lead.
At this point, the chip solder ball melts and then cools for optimal strength.
4, The correct use of flux
Whether it is resoldered or repaired directly, we need to apply the flux first.
To weld the chip, use a small brush to apply a thin layer to a clean pad.Spread as much as possible.Do not brush too much, or it will affect the welding.
During repair welding, you can apply a small amount of flux around the chip using a brush.
For flux, use flux for BGA welding.
5. BGA welding must be accurately aligned.
This should be fine since everyone's rework table is equipped with infrared scanning imaging assist alignment.
If there is no infrared assistance, we can also refer to the box line around the chip for calibration.
Note that the chip should be placed as close to the center of the box line as possible.The small deviation is not a big problem, because the ball will have an automatic return process when it melts, and the small deviation will automatically return to the positive position.