As we know, solder paste printing is an essential section in the process of SMT (Surface Mount Technology). Due to the solder paste is a mixture of powder and flux, its fluidity demonstrates the printing process. Viscosity is mainly illustrating the form of solder paste fluids. If it has low viscosity, it flows easily for filling and collapses. On the contrary, if it has high viscosity, it is easy to roll, peel and form. The requirement of viscosity is also changing at different stages of solder paste printing accordingly. SMT has a flexible requirement of viscosity but fortunately viscosity itself is a variable that is easy to change. This requirement of varying viscosity places a higher dependence on the solder paste printing process and the printer's parameter settings.
The reason for the importance of a solder paste printer is that it is sometimes extremely thin and will cause the damage of the product due to the small amount of solder paste after the furnace is completed.
1. The quality of steel plate
Stencil printing is contact printing, both of the thickness of the stencil and the size of the opening are decided by the amount of solder paste proceed to print.
Not only too much solder paste will produce a short circuit, but also too little solder paste will produce solder shortage at the solder joints,the template and shape of the opening and the smoothness of the opening which can also affect the quality of the release.
Furthermore, the template opening is required to make a bell-shaped mouth, otherwise the solder paste will be removed from the chamfering of the bell jar during demolding.
2. The printing process parameters
Solder paste is a thixotropic fluid. When the paste is viscous, the scraper will move forward at a certain speed and angle to push the solder paste into a roll in front of the scraper as the result of injecting the solder paste into the pressure in the mesh or the leak hole.
The viscous friction of the solder paste causes the solder paste to shear at the intersection of the squeegee and the stencil. The shearing force then reduces the viscosity of the solder paste thereby facilitating smooth injection of the solder paste into the mesh. The requirement of a certain balance is related to the speed, pressure and angle of the blade with the stencil and the viscosity of the solder paste. The quality of solder paste printing is assured by accurately controlling these parameters.
Different printing parameters will affect the volume of the solder paste. Due to the increase of speed, the volume of the solder paste will increase at first and then decreases accordingly. As the pressure increases, the solder paste volume will increase and decrease quickly during the process. The faster the stripping, the larger the volume. The larger the gap, the larger the volume. The maximum value of the volume change of the solder paste is affected by many factors. The change caused by the speed and the grade are the largest variables. This is followed, in order of significance, by the printing gap, the peeling speed and the pressure as the least influential factor. For an SMT solder paste printing process it is important to keep in mind the effect each variable has. Proper engineering of these parameters can help produce appropriate stencils for your product, different tin thicknesses and more reliable quality.
At Fumax, we have the necessary SMT technologies for supporting PCB and PCBA production. Also, we provide other methods of PCB/PCBA such as DIP (through hole assembly) for meeting your requirement. We are an ISO9001 certified Contract Manufacturer in South China. We aim to offer best quality and satisfactory products for clients.