In SMT placement, thick copper boards often suffer from large thermal capacity of the copper layer and delayed temperature rise, which requires solder ODM R&D to simultaneously optimize the matching between the Flux activation temperature window and the alloy melting range. Otherwise, problems such as excessive solder joint void rate and thin, discontinuous IMC layer are likely to occur. In an 8oz thick copper power module project of JiajinYuan, we lowered the liquidus temperature of the Sn96.5Ag3.0Cu0.5 alloy to 217.2°C, while adjusting the Tg value of the rosin matrix from 68°C to 62°C, so that the active ingredients start to release at 150°C, which exactly covers the key heat absorption range of the thick copper board from 140°C to 200°C.

High-frequency boards impose more stringent requirements on solder ODM R&D. It is necessary not only to control the Cl? content below 30ppm, but also to avoid high-frequency signal attenuation caused by nitrogen-containing activators. We adopted a modified rosin-organic acid composite system to replace the traditional DBU catalyst. While ensuring that the solder joint tensile force at the peak temperature of 230°C is ≥4.2N, the surface insulation resistance of the PCB is maintained above 1.8×1011Ω in the 1GHz frequency band. This data is measured on the Rogers RO4350B substrate provided by JiajinYuan's customer, without any theoretical conversion.

To address the tin bead splashing phenomenon that easily occurs at the edge of thick copper board pads, the solder ODM R&D team tightened the metal powder D50 from 25μm to 22.3μm, increased the proportion of -325 mesh fine powder to 38%, and increased the addition amount of hydrogenated castor oil derivative in the vehicle from 0.75wt% to 0.92wt%, extending the rebound time of the Solder Paste to 0.8 seconds after the squeegee pressure is removed. This not only suppresses the trailing at the edge of the stencil opening, but also avoids poor demolding caused by excessive thixotropy.

Ion chromatography analysis of residues after reflow of high-frequency boards shows that the residual peak of sebacic acid in conventional formulations reaches 12.6μg/cm2, while the formulation adjusted by solder ODM R&D reduces it to ≤4.1μg/cm2. This is achieved by compounding adipic acid and undecylenic acid at a molar ratio of 1:0.65, and introducing a trace amount of ethylene glycol monobutyl ether acetate into the solvent system. It can preferentially volatilize during the 185°C holding stage and carry away part of the organic acid salt precursor, thereby reducing the deposition of high-temperature decomposition products.

Actual measurement on JiajinYuan's production line shows that this solder ODM R&D achievement achieves a primary soldering yield of 99.23% on a 6-layer high-frequency hybrid board (including 2oz high-frequency copper + 4oz thick copper ground layer), an increase of 1.6 percentage points compared to the originally used imported solder paste. Among them, the void area ratio detected by X-ray at BGA device solder joints decreased from 18.7% to 9.3%, and the AOI false alarm rate decreased by 42%. This indicates that formula debugging not only improves metallurgical bonding, but also significantly reduces optical recognition interference sources.