Chip reballing is not as simple as just applying Solder Paste and calling it a day. It requires the reballing solder paste to fully wet the interface between the pads and the chip solder balls during the reflow process. This demands that the reballing solder paste must have sufficiently high activity, a precisely matched alloy melting point window, and an alloy powder particle size that is fine enough and evenly distributed. Otherwise, batch defects such as cold solder joints, solder balls, insufficient solder climb, or excessive voiding rate are likely to occur. In recent years, Domestic Solder Pastes have broken through multiple process bottlenecks in rosin-based halogen-free systems. For example, our JJY 8MQP/5RQ series uses T4-grade 0307 alloy powder, paired with ROL1-grade low halogen control (both items <1500ppm). On QFN devices, the measured solder climb rate reaches 95%~99%, far exceeding the industry's common level of 70%~85%. Behind this is the deep coupling between the Flux active components and the ability to remove the oxide film on the metal powder, which cannot be solved by simply increasing the rosin content.

Different chip packages have vastly different thermal sensitivity requirements for reballing solder paste. Communication base station main control chips need to balance high-temperature stability and low voiding rate. In this case, the 8M9P/5RR zero-halogen formula shows its advantages. Its 0ppm halogen residue, paired with the 217℃ eutectic point of 305 alloy powder, stably controls the voiding rate within 3% at a peak temperature of 245℃. On the same platform, although 8MTSP/5RTS has slightly higher activity, its halogen content reaches 500ppm. After long-term aging, ionic residues can easily induce micro-short circuits, which has been repeatedly verified in the reballing of automotive radar chips. Therefore, when selecting chip solder paste, one cannot only look at the initial soldering effect, but also reverse-infer the halogen threshold based on the lifespan requirements and failure modes of the end product.

High-density, fine-pitch chips such as mobile phone fingerprint modules have extremely stringent requirements for the rheological properties and residue transparency of reballing solder paste. The 8MNTTP/5RNTT not only reduces halogen to the 100~200ppm ROL0 level, but more importantly, it introduces 00507BN and 00507B2N dual-nickel doped alloy powders. On the basis of T5-grade fine powder, it further suppresses the excessive growth of intermetallic compounds during reflow, avoiding solder joint embrittlement. Meanwhile, the residue is transparent and does not affect AOI optical recognition. This has been proven in the mass production of a certain Huawei flagship model to reduce the rework rate by 0.18 percentage points. Conventional T3/T4 powders, even if they meet the activity standard, often cause false positives and missed inspections due to whitish residues.

Laser reballing is becoming the mainstream method for BGA rework and micro sensor repair. Traditional solder pastes are extremely prone to splattering or forming solder balls under instantaneous laser heating. However, the 8MLJ series adjusts the rosin softening point and thixotropic index, allowing the solder paste to maintain its shape stability during 10ms-level pulse heating. Paired with T6/T7-grade ultra-fine powder, it achieves solder ball-free soldering. Measured under the composite process of jet valve dispensing + infrared laser, the first-pass yield of 0.3mm pitch QFN reballing reaches 99.2%, which is 1.7 percentage points higher than that of the ordinary 8MQP/5RQ. This shows that Domestic Solder pastes have moved from the "usable" stage to the "specialized optimization" stage. Chip solder paste is no longer a general consumable, but a core process element that requires customized matching according to equipment type, heating method, and substrate material.