Analysis of Solvent Properties in Solder Paste Cleaning

<p> Changes in environmental conditions (such as temperature and relative humidity) in the printing area will directly affect the viscosity change of the solder paste. If the temperature rises, the viscosity will decrease, the solder paste will be deposited irregularly, and the oscillating disc will collapse. The temperature will decrease and the viscosity will increase. When the relative humidity becomes large, the solder paste absorbs moisture. The printing operation is required to be carried out at a suitable temperature and relative humidity, and the temperature is generally controlled at 20 ° C and the relative humidity is about 65% HR.

When the stencil's stainless steel foil and the surrounding screen are improperly tensioned to make the tension unbalanced, the stencil will be displaced during printing, causing the solder paste to deviate from the land pattern. This offset will be more as the squeegee pressure increases. Obviously prominent. The selection of the stencil frame should be appropriate so that the ratio of the printed area to the entire stencil area is 1/9, and the edge of the printed graphic to the frame margin is required to be at least 10 cm. When the stencil frame area is too small and the printing area is too large, When the contact printing is performed, the amount of solder paste deposited on the edge of the printed pattern is uneven.

The cleaning methods of the stencil include dry cleaning, wet washing, ultrasonic and vacuum washing. If the template is not cleaned in time, the solder paste will remain on the opening and the inclined surface of the hole wall. After drying and solidifying, the opening is blocked, and the cleaning frequency is insufficient or the cleaning method is improper, which may cause poor printing.

It is usually first wet-washed with alcohol, then rubbed with a non-woven fabric or blown with a wind gun. It can also be cleaned by ultrasonic machine and special solvent, but when the whole stencil is immersed in cleaning, pay attention to the solvent resistance of the adhesive and the impact force on the stencil, and also consider the influence of heating on the thermal expansion coefficient of aluminum frame, wire mesh and stainless steel to avoid Degumming and graphic deformation.

The stencil should be properly stored after cleaning and placed on a special formwork to prevent collision, damage and distortion.

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