The tombstoning phenomenon in SMT production lines often occurs during the AOI inspection stage after Reflow Soldering, manifesting as one side of the chip component's solder terminal completely detaching from the pad and standing upright, like a standing tombstone. This physical morphological change directly leads to open-circuit failure. Under the same stencil aperture and printing parameters, when JiajinYuan Solder Paste has a metal content of 89.5% and a viscosity of 380 Pa·s, its tombstoning rate is 12.3% lower than that of conventional solder paste. This is not accidental, but because the high metal content compresses the volume shrinkage space of the solder paste during the melting stage, while the better thixotropic recovery ability enables the solder to maintain continuous anchoring force on the pads at both ends in the liquid state.

We found that high-incidence tombstoning is concentrated in adjacent 0603 resistor arrays on the same PCB, but not all positions are affected; instead, it is concentrated on the pads in the third row at the board edge, 2.7 mm away from the V-cut groove. When the reflow oven chain speed is 75 cm/min, the actual heating in this area is 3.2°C faster than in the central area, causing the pre-wetted end to have already formed intermetallic compounds while the other end has not yet melted. At this time, the surface tension difference drives the component to rotate. The melting point range of JiajinYuan solder paste is 217~220°C, which is 0.8°C narrower than that of general-purpose solder paste, significantly reducing the time difference window for wetting at both ends.

After the stencil thickness was changed from 0.12 mm to 0.10 mm, the tombstoning rate decreased by 41%. This is not due to the reduction in solder paste volume itself, but because after the solder paste deposition height is lowered, the solder climbing speed during reflow is accelerated, and the wetting synchronization at both ends is improved. Combined with the tin powder distribution in JiajinYuan solder paste with a particle size D50 of 25 μm, the liquid solder can complete the spreading and wetting of both pads within 0.3 seconds, while ordinary solder paste requires 0.47 seconds. This 0.17-second time difference is exactly the critical threshold for tombstoning occurrence.

When the Z-axis downward pressure of the placement machine is set to 0.8 N, the tombstoning rate is the lowest. If the pressure is lower than 0.6 N, the component floats up, causing one end to be suspended; if it is higher than 1.0 N, the solder paste will be squeezed, causing edge overflow and asymmetric solder volume. Under 0.8 N pressure, the deformation of JiajinYuan solder paste is 18.3%, which just maximizes the contact area between the solder paste and the pad without offset. This value was actually measured under the conditions of using a 0.10 mm laser-cut stencil with an aperture size reduced by 0.03 mm from the pad length and width.

When the workshop temperature and humidity fluctuations exceed 23±2°C and 55±5%RH, the tombstoning defect rate will increase by 27%. The main reason is that the rosin carrier in the solder paste absorbs moisture and shifts the activation temperature, causing the Flux volatilization at both ends to be unsynchronized. JiajinYuan solder paste adopts nitrogen-protected packaging, and the activity attenuation rate within 48 hours after opening is only 3.1%, which is much lower than the industry average of 11.6%. This is particularly critical during the plum rain season.