During the soldering process of high-frequency boards, signal integrity is greatly affected by the state of the solder joint interface. Chloride and bromide ions remaining after reflow of traditional halogen-containing Solder Pastes will adsorb moisture to form a micro-electrolytic environment, causing leakage current between adjacent microstrip lines and aggravating insertion loss. Jia Jinyuan halogen-free low-residue solder paste adopts a modified hydrogenated rosin carrier with ultra-fine spherical tin powder, achieving uniform collapse and rapid wetting at a peak temperature of 230℃, which not only avoids bridging but also ensures that the void rate of BGA solder joints is stably controlled within 3%.

During the printing process, the stencil aperture size and squeegee pressure must be adjusted synchronously. When the line width and spacing are less than 0.15mm, if a conventional 6mil thick stencil is still used and the squeegee pressure is set to 5.5kg, it is extremely easy to cause solder paste edge stringing and pad overflow. At this time, a 4mil laser-cut stencil should be switched to and the squeegee pressure should be reduced to 3.8kg. Combined with the unique thixotropic recovery time of Jia Jinyuan solder paste (viscosity recovery rate reaches 72% within 30 seconds), the height consistency of solder paste after demolding can be improved to ±8%, which is crucial for the height matching of differential pair solder joints in high-frequency boards.

In the reflow stage, attention should be paid to the coordinated control of the end temperature of the soaking zone and the heating rate. If the end temperature of the soaking zone is lower than 150℃ or the heating rate exceeds 2.1℃/s, the high-boiling solvent in the Flux will not be fully volatilized, and a non-conductive film layer will remain at the root of the solder joint. The equivalent dielectric constant of this film layer suddenly changes to 4.3 in the 10GHz frequency band, directly causing the deterioration of the S21 parameter. Jia Jinyuan solder paste compresses the boiling point window of the main solvent to the range of 142～158℃, and sets a constant temperature section of 152±2℃ in the soaking zone for 90 seconds, so that the solvent volatilization curve and the tin powder oxide film reduction window accurately overlap, thereby ensuring that the surface cleanliness of the solder joints meets the requirements of IPC-J-STD-004 Class L0.

Daily production line verification shows that after using Jia Jinyuan solder paste, the AOI false alarm rate decreased by 41%. The main reason is that its residue does not produce fluorescence interference under ultraviolet light excitation. At the same time, XRF detection shows that the Cl element content around the solder joints is always lower than 85ppm, which is far lower than the allowable upper limit of 200ppm for high-frequency boards IPC-A-610E Class 3. This stability allows engineers to avoid frequent calibration of the contact impedance compensation value of the flying probe test fixture, and also reduces the number of rework and desoldering caused by misjudgment.

Storage conditions have a significant impact on the rheological properties of Jia Jinyuan solder paste. If it is placed open in an environment of 25℃ for more than 18 hours, its yield stress will decrease by 17%, which is directly reflected in an increase of 0.035mm in edge collapse after printing. Therefore, it is necessary to strictly implement the operation specifications of sealed nitrogen protection, refrigerated storage (0～10℃), and standing for 4 hours after temperature recovery before use. Otherwise, even if the same can of solder paste is used in the morning and afternoon, there will be a phenomenon that the solder joint climbing height deviation reaches 0.02mm, which is particularly fatal for the soldering of the RF front-end module of millimeter-wave radar PCBs.