Solder Balls

1. PCB silk screen holes are misaligned with the PCB pads, causing inaccurate printing that contaminates the PCB with solder paste.

2. The solder paste is exposed to excessive oxidation in a humid environment.

3. Heating is imprecise, slow, and uneven.

4. The heating rate is too rapid with overly prolonged preheating intervals.

5. The solder paste dries too quickly.

6. Insufficient flux activity.

7. Presence of excessive tin powders with fine particles.

8. Inappropriate flux volatility during the reflow process.

The process acceptance criteria for PCB solder balls stipulates: when the spacing between pads or printed wires is 0.13mm, solder ball diameters should not exceed 0.13mm, and no more than five solder balls should appear within a 600mm² area.

Bridging: Solder bridging typically occurs due to excessively thin solder paste, which may result from low metal or solid content, inadequate thixotropy, easy paste expulsion, or excessively large solder particles. Additionally, insufficient surface tension of the flux, excessive solder paste on the pad, or excessively high peak reflow temperature can contribute to this issue.

Open: Reason:

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This revision maintains the structure and line numbering of the original while improving clarity and readability.

1. The amount of solder paste is insufficient.

2. The coplanarity of component pins is inadequate.

3. The solder is not sufficiently wet (it doesn’t melt well, and its fluidity is poor), and the solder paste is too thin, leading to solder loss.

4. Pins suck solder (like rush grass), or there are nearby via holes. Pin coplanarity is especially critical for fine-pitch and ultra-fine-pitch components. One solution is to pre-apply solder to the pads. To prevent pin sucking, slow down the heating rate, increase the heat on the ground plane, and reduce heating on the top. Alternatively, use flux with slow wetting speed and high activation temperature, or solder paste with different Sn/Pb ratios to delay melting and reduce pin absorption.

Emergency Treatment of BGA Packaged Integrated Circuit Soldering

As high-density, high-performance, multi-pin PCB integrated circuits increasingly adopt ball grid array (BGA) packaging, such as high-speed processors and decoders, they generate significant heat. Due to the BGA chip’s pins being directly underneath it, the connection between the chip pins and the circuit board pads via solder balls can weaken due to chip heating. This cannot be fixed with a regular soldering iron. The optimal repair method involves resetting the solder balls on the chip and re-soldering them using a BGA soldering station, equipment not typically available to general repairers.

Blow-soldering the chip with a hot air gun carries risks, but with proper technique, it can resolder the chip to the circuit board. Emergency methods for dealing with virtual soldering of BGA packaged integrated circuits under amateur conditions include:

1. Use of solder paste: This removes oxide layers from PCB components, reduces solder surface tension, and enhances fusion between solder balls and pads. The solder paste should be neutral and non-corrosive. It appears as a light yellow viscous substance. Apply the paste around the chip using a screwdriver, then use a heat gun at low temperature to heat the solder paste around the chip until it drips onto the chip. Move the circuit board in four directions while heating multiple times to allow more solder paste to infiltrate the solder balls.

2. Heat the chip with a hot air gun, preferably using medium to high temperature settings. Direct the air flow vertically onto the chip substrate. Move the air nozzle clockwise or counterclockwise at a consistent speed around the chip’s circumference to ensure even heating. Proper control of heating duration is crucial: too short and the solder balls won’t melt properly, resulting in poor soldering; too long and the solder balls may burst, causing short circuits and chip damage. Watch for the reaction of the solder paste — stop heating immediately if slight blue smoke appears, indicating the solder paste is boiling and evaporating.

3. Apply moderate pressure in the middle of the PCB chip using a screwdriver. This ensures good contact between the solder balls and the chip and PCB. Once the temperature drops (no longer hot to the touch), release the pressure. After this treatment, the equipment may be repaired.