Aiming at the common edge collapse problem in solder paste printing for thick boards, this paper starts with the collaborative optimization of solder paste rheological properties, stencil aperture design and squeegee parameters, proposes a solder paste selection standard for thick boards adapted to PCB thicknesses above 0.8mm and a tightening scheme for the solder paste printing process window, and emphasizes that yield improvement can be achieved through solder paste viscosity gradient matching and fine-tuning of the standing time before reflow without replacing equipment.

01005 component soldering is currently one of the most challenging process bottlenecks on SMT production lines. Its 0.4mm×0.2mm size, 0.12mm pad pitch, and extremely low heat capacity require solder paste printing accuracy of ±15μm, placement repeatability ≤±10μm, and reflow peak temperature fluctuation controlled within ±2℃. The measured yield of Jiajinyuan JTY-806 solder paste paired with JTS-300 placement machine is stable at 99.2%～99.5%, but at least 3 rounds of fine-tuning are still required for the first article after line changeover to meet the standards.

Solder OEM contract manufacturing produces solder according to customer formulations, preserving original process performance. It can accurately replicate solder paste rheological properties, wetting speed, and reflow sphere formation consistency, avoiding printing slump, increased solder joint void rate, and ICT test misjudgment caused by raw material substitution or process adjustments. It is especially suitable for high-density BGA, 01005 components, and automotive-grade thermal cycle verification scenarios.

Post-printing solder paste placement failure and downtime stencil cleaning time directly determine the SMT first-pass yield. If solder paste remains on the stencil for more than 15 minutes, obvious slump, oxidation, and viscosity increase will occur. If stencil cleaning is delayed for more than 30 minutes after downtime, dried residual solder paste will cause solder spikes and insufficient solder in the next batch of printing. The production line must dynamically set the effective window after solder paste printing and the stencil cleaning response threshold based on solder paste type, workshop temperature and humidity, and printing frequency.

During soldering of ENIG boards, the wettability of solder paste directly affects the formation quality of solder joints. Jiajinyuan solder paste demonstrates excellent spreading ability and low void rate on ENIG boards. With a conventional reflow profile, it can achieve full solder joints, complete pin wrapping, and eliminate common production line defects such as solder spikes and cold solder joints.

Due to the large heat capacity and slow heating rate of thick copper plate welding, wave soldering is prone to missing solder. Selecting high-wettability solder bars can significantly improve the spreading ability of molten solder on thick copper substrates. Combined with the collaborative optimization of process parameters such as increasing the preheating temperature to 130℃～140℃ and reducing the chain speed to 1.0m/min～1.2m/min, it effectively solves problems such as insufficient solder joints, bridging defects, and cold solder on the back of the PCB.

The selection of eutectic solder must closely focus on the two key hard indicators of melting point and ductility, as the melting point directly determines the width of the reflow profile window, while ductility affects the thermal fatigue resistance of solder joints. Jia Jinyuan's Sn63Pb37 eutectic solder melts precisely at 183℃ with an elongation rate stably above 45%, making it a reliable choice for mass production of automotive controllers and industrial power boards.

Excessive solder paste volume on multi-pin pads is one of the main causes of bridging and solder ball defects on SMT production lines. For Jiajinyuan solder paste, if the printing thickness exceeds 140 μm under a 0.12 mm stencil opening, solder bridges are highly likely to form between fine-pitch devices such as QFP and SOIC. Meanwhile, solder balls may form due to bursting caused by obstructed escape of flux vapor during reflow.

Void X-Ray inspection identifies the internal void distribution of solder joints through high-precision imaging, and quantifies the void rate using an area ratio algorithm. When the void rate exceeds the 5% threshold specified in IPC-A-610, it is judged as non-conforming. This method has been batch-verified on the Jiajinyuan production line, significantly reducing the missed detection rate of BGA cold solder joints.

Based on real cases from SMT production lines, this paper details the verification methods for the insulation performance of the no-clean solder paste process, covering three core solder paste testing methods: ionic contamination testing, surface insulation resistance (SIR) testing, and post-reflow ICT open-circuit retesting. It emphasizes the direct impact of no-clean solder paste residues on the risk of leakage between micro-pitch solder joints under BGA packages.

A domestic solder source factory directly supplies a full range of soldering materials including solder paste, solder wire and solder bar. Jia Jinyuan's production line measured solder paste release rate exceeds 98.5%, and the wetting angle after reflow is ≤35°. It supports providing SGS test reports and ROHS2.0 compliance certificates by batch, meeting the strict control requirements for metal composition segregation and halogen residues in automotive electronics and medical equipment.

The process window setting for lead-free solder paste reflow soldering must balance the coordinated control of peak temperature and soaking zone. Jia Jinyuan lead-free solder paste performs stably in the peak temperature range of 235°C to 245°C. However, if the soaking zone temperature is below 150°C and the duration is less than 60 seconds, it can easily lead to poor wetting and increased void rate. In actual production lines, the conveyor speed and the power of each temperature zone need to be dynamically adjusted based on the measured curves from a temperature profiler.

The one-stop provision of PCBA soldering materials must closely align with the actual needs of the production line. As a core material, solder paste must match stencil apertures, reflow profiles, and component spacing. Jia Jinyuan solder paste shows no obvious slump during 24 consecutive hours of printing on 0.3mm pitch QFN. When paired with flux of the corresponding activity level, low-oxygen solder wire, and high-purity solder bar, it ensures consistent yield in SMT placement and manual soldering rework.

Cold solder joint is one of the most frequent soldering defects on SMT production lines. Pad oxidation and insufficient flux activity are the two main causes: the former prevents solder paste from wetting the copper surface, while the latter makes the oxide film difficult to remove. When the two factors overlap, the incidence of cold solder joint can increase by more than 3 times. The Jiajinyuan JHY-805 series flux has a measured wetting angle of <25° on OSP boards, effectively suppressing the formation of cold solder joints.

Solder for 5G equipment must maintain zero solder joint cracking under complex operating conditions such as high-frequency vibration, wide temperature cycling, and high humidity and salt spray. Jiajinyuan's halogen-free high-reliability solder, through optimizing the SnAgCu main alloy ratio and the compounding of nano-scale active flux, achieves a solder joint shear force attenuation of <8% after 500 cycles of thermal shock from -40°C to +125°C, with a halogen content of <900ppm, fully meeting the long-term reliability requirements for 5G equipment solder in high-density interconnect scenarios such as 5G base station RF modules and millimeter-wave antenna arrays.

The sphericity, particle size distribution, and oxidation level of tin powder particles in SAC solder paste directly affect the release integrity and pad coverage during solder paste printing. Actual production lines have found that spherical tin powder with a D50 of 25μm can achieve a release rate of over 92% on a 38μm aperture stencil. When the D50 deviation exceeds ±1.5μm or the oxygen content is >0.5wt%, the defect rates of solder bridging and insufficient solder increase by more than 3 times. The process compatibility of solder paste, SAC solder paste, and tin powder solder paste must be based on measured particle parameters.

During PCB pad processing, the soldering performance of ENIG, Immersion Silver and OSP processes differs significantly. The ENIG layer is oxidation-resistant but has poor wettability, requiring high-activity solder paste. Immersion Silver is prone to sulfidation discoloration and sensitive to reflow peak temperature. Uneven OSP film thickness can cause local non-wetting. The three processes must be managed differentially in stencil aperture design, reflow profile setting, and incoming material storage conditions.

During the pin dip soldering process, oxidation of the solder bath surface is the main cause of continuous dross generation. Jiajinyuan anti-oxidation flux, through the synergistic effect of dynamic coverage and active ingredients, forms a dense inert film on the solder bath surface, reducing the oxidation rate by more than 70% during pin dip soldering, cutting daily dross production by 1.2kg, significantly extending the cleaning cycle of the solder pot, and stabilizing solder joint wettability.

01005 packaged components, with their extremely small pad dimensions and narrow solder paste volume tolerance, are a high-incidence area for solder beads. Residual solder beads can easily cause creeping discharge and breakdown during high-voltage testing, directly threatening the insulation reliability of products. Production line data from Jiajinyuan shows that this type of defect accounts for 68.3% of the total solder bead incidence, requiring coordinated control from three aspects: stencil aperture design, squeegee pressure, and reflow atmosphere.

To address persistent issues such as uneven solder paste deposition, cold soldering, and solder bridging during thick copper foil soldering on multilayer boards, this paper draws on 20 years of measured data from Jia Jinyuan's production lines, focuses on precise solder paste dosage control methods, and details the matching logic for thick copper solder paste printing parameters, covering key actions such as stencil aperture design, squeegee pressure and speed coordination, and SPI detection threshold setting before reflow soldering.