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Introduction To Chip-level Maintenance
Jan 10, 2019

1. What are the melting points of lead-tin and lead-free solder balls respectively?

The melting point of lead-tin ball is 183 degrees and that of lead-free tin ball is 217 degrees.

2. How to set the temperature when it is uncertain whether the plate is lead-free or lead-free?

First, according to the lead temperature setting, after heating, gently touch the BGA chip with tweezers. If the chip can move smoothly, it means that the welding is successful. If the chip can not move, it means that the solder may be lead-free. Change the temperature setting to lead-free. After heating, gently touch the BGA chip with tweezers to confirm whether the welding is successful.

3. How many kinds of insulating tapes are there?

There are two kinds of commonly used heat insulation tapes:

One is made of aluminium and platinum, silver white, with good heat insulation effect and fragile shortcomings.

The other is fiberglass backing glue, which has comprehensive color and good toughness. The disadvantage is that the heat insulation effect is poor.

Users need to choose according to their usage.

4. What role does solder paste play?

The solder paste can remove the oxide on the surface of the solder pad and enhance the activity of solder.

5. What is the difference between hot air heating and infrared heating?

For BGA repairing bench heated by hot air, air flow may cause component displacement. Air flow leads to hot air unable to directly heat BGA chip tin planting balls, otherwise tin balls may stick together (some of the direct heating steel mesh can be used).

In addition to temperature control, but also to control the air flow, so hot air heating BGA repair bench is often more complex in structure, bulky and bulky.

Hot-air BGA repair bench needs to be heated in stages. It needs to set complex temperature parameters. Users need to master 100-200 temperature curves skillfully. Different circuit boards need different temperature curves. It may be difficult for novices to choose a suitable set from different temperature curves.

Hot air type BGA repair bench must be connected to the computer to ensure higher work efficiency. Hot air repairing platform requires high placement of circuit boards. BGA chips should align the air nozzles very accurately. If the circuit board and BGA chips are misaligned, the welding will fail.

Infrared heating is a new technology developed in recent years. Infrared heating BGA repair table has simple structure, accurate temperature control and easy operation.

6. What is the reason for PCB distortion?

There are two reasons for PCB deformation: one is that the preheating area is too small and the PCB is not uniformly heated; the other is that the PCB is unreasonable, uneven and not clamped.

7. How to solve the problem of virtual welding?

It can be welded directly. First, add proper flux or perfume to the chip, then heat it.

If the welding is unsuccessful, the chip needs to be removed and replaced by BGA.

8. How to align the BGA chip with the pad of the circuit board?

There is a border line corresponding to the BGA chip on the circuit board, and the BGA chip can be aligned with the border line.

For BGA chips with tin sphere spacing over 0.65 mm, manual alignment can be used directly without the help of professional optical equipment. For example, notebook computer board, desktop computer motherboard, industrial computer board, server board, large and medium game board...

For BGA chips with tin sphere spacing less than 0.5mm, optical devices are often needed to align them accurately. For example, digital cameras, mobile phones and other small electronic products.

Commonly used optical devices are magnifiers (about 10 times magnification), microscopes (more than 50 times magnification), and various special optical alignment systems.

9. What is the distance between the solder pads of laptop computers? How big are the tin balls for laptops?

There are three kinds of pad spacing for notebook computers: 1.27mm 1mm 0.8mm

There are three kinds of tin balls for notebook computers: 0.76mm, 0.6mm and 0.5mm.

The chip with 1.27mm spacing uses 0.76mm tin balls.

The chip with 1 mm spacing uses 0.6 mm tin balls.

Among them, the chip with 0.8mm spacing uses 0.5mm tin balls.

10. X-ray machine can detect whether the BGA chip is welded or not?

X-ray machine can accurately judge the failure of tin ball adhesion.

For the problem of virtual welding, X-ray machine can not accurately judge.

The X-ray machine can not judge the damage caused by overheating of core.

The price of X-ray machines ranges from 20 to 1 million yuan.

Functional testing is the most accurate way to judge whether welding is successful or not. To put it bluntly, it is to test whether the circuit board can work properly by electrification.

11. What is infrared heating?

Infrared light is one of the many invisible rays in sunlight, located outside the red light, so it is called infrared. In the spectrum, the wavelength range from 0.76 to 400 microns is called infrared, which has thermal effect.

12. Is infrared heating glaring?

Infrared light is invisible, so it won't dazzle. Incandescent lamps are often dazzling.

13. Under what circumstances should tin paste be used? Under what circumstances do you use tin balls?

The size of BGA chips used in small electronic products such as mobile phones and digital cameras is very small. The pads on the chips are very small and the distance between the pads is very small. It is suitable to use tin paste to form tin balls on BGA chips.

BGA chips used on large circuit boards, such as computers, large game consoles, industrial computers and LCD TV, are often of large size, with large pads on the chips and large pads spacing. In order to ensure the uniformity of the size of the formed tin balls, it is better to use tin balls.

14. How many kinds of steel nets are used for planting tin balls?

Generally speaking, there are two kinds: one is non-direct heating; the other is direct heating.

Indirect heating

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