Recently, in response to an urgent request from a smart terminal manufacturing enterprise in South China, Jia Jinyuan's technical team dispatched a special team consisting of senior SMT process engineers and Solder Paste application experts to the factory of a customer specializing in custom motherboards in Longhua, Shenzhen, to provide five days of on-site technical support. The team participated in all stages including solder paste printing, chip mounting, Reflow Soldering, and AOI inspection, systematically investigating the root causes of frequent solder bridging and tombstoning in QFN-packaged devices. It was found that the customer's original solder paste exhibited insufficient wetting and spreading on pads with a pitch below 0.4mm, weak synchronization of alloy melting during the reflow phase, and that the stencil aperture and squeegee pressure parameters were not closed-loop adapted to the current solder paste rheological properties.

Based on a comparison of on-site measured data with historical batch solder paste performance profiles, the technical team quickly identified two halogen-free, lead-free high-temperature solder pastes, LFP-JJY5RQ-0307T4 and LFP-JJY5RNTT-305, as alternative solutions. The former features ROL1-level low halogen content and a high-activity rosin system, making it particularly suitable for high-density solder climbing scenarios. The latter, with its ultra-low halogen control of 100~200ppm and 00507BN/T5-grade ultra-fine alloy powder, achieves stable performance with transparent residues and a void rate below 0.8% in high-precision applications such as communication modules and fingerprint lock motherboards. Both the Sn99Ag0.3Cu0.7 and Sn96.5Ag3Cu0.5 alloy systems can achieve sufficient melting and interfacial metallurgical bonding within the 240~255℃ range, effectively suppressing tombstoning tendencies caused by solder surface tension imbalance.

After synchronously adjusting the stencil thickness from 120μm to 100μm, optimizing the squeegee angle to 60 degrees, and fine-tuning the peak temperature of reflow oven Zone4 to 252℃, data from three consecutive trial production batches on the customer's production line showed that the tombstoning rate for QFN0.35mm devices dropped from the original 3.7% to 0.12%, solder bridging defects decreased by 92%, and the AOI first-pass yield increased from 92.4% to 99.6%. Moreover, the solder joint IMC layer was uniform and dense, and the shear strength compliance rate remained stable above 99.3%, verifying the critical value of collaborative optimization between solder paste bulk performance and the SMT process window.

This on-site support not only achieved a closed-loop resolution of the issues but also assisted the customer in establishing a solder paste batch performance ledger and a dynamic reflow profile calibration mechanism. Over ten Jia Jinyuan halogen-free, lead-free solder pastes, including 8MQP/5RQ, 8MNTTP/5RNTT, and 8M9P/5RR, were classified and archived according to device type, pad size, and thermal sensitivity level. Additionally, LFP-JJY5RW1-0307 water-washable solder paste was provided for heat sink aluminum substrate rework scenarios, and LFP-JJY5RG-In52Sn48 ultra-low temperature solder paste was supplied to meet flexible circuit mounting requirements, forming a full-scenario solder paste solution matrix covering high-temperature, medium-temperature, low-temperature, and special material soldering.

Currently, the customer has included Jia Jinyuan solder paste in the preferred BOM list for new projects and plans to fully introduce the LFP-JJY5RLJ-305 series, adapted for laser jet valves, into three new high-speed SMT lines for next quarter's capacity expansion, to support the customer's welding consistency and yield assurance requirements under the goal of doubling production capacity for Bluetooth earphones and TWS modules.