SMT chip processing short-circuit bad phenomenon

SMT chip processing short-circuit bad phenomenon mostly in the fine pitch IC pins, mostly in the 0.5mm and the following pitch between the IC pins, because its spacing is small, improperly designed template or printing a slight omission is very easy to produce. One of the reasons for this is the printing method of the solder paste printer: the current printing method is divided into "contact printing" and "non-contact printing". The printing method with a gap between the stencil and the PCB is "non-contact printing", with a general gap value of 0.5 to 1.0mm, which has the advantage of being suitable for different viscosities of solder paste. The printing method without a gap between the stencil and the PCB is called "contact printing". It requires the stability of the overall structure, suitable for printing high-precision solder stencil and PCB to maintain a very flat contact, after the printing is complete before disengaging from the PCB, so the way to achieve high printing accuracy, especially for fine pitch, ultra-fine pitch solder paste printing. Another reason is the height of the mounting, for 0.5mm IC in the mounting should use 0 distance or 0 ~ 0.1mm mounting height, in order to avoid because the mounting height is too low and make solder paste molding collapse, cause short circuit when return flow. Do you think there are other reasons apart from these two reasons?

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