2.2 After plugging the holes with aluminum sheets, directly screen the solder mask on the board surface
In this process, a CNC drilling machine is used to drill out the aluminum sheet that needs to be plugged to make a screen plate, which is installed on the screen printing machine for plugging. After the plugging is completed, it should not be parked for more than 30 minutes. The process flow is: pretreatment – plug hole – silk screen – pre-baking – exposure – developing – curing
This process can ensure that the via hole is well covered with oil, the plug hole is flat, and the color of the wet film is the same. Pad, resulting in poor solderability; after hot air leveling, the edge of the via hole foams and oil is removed. It is difficult to control the production using this process method, and the process engineer must adopt special processes and parameters to ensure the quality of the plug hole.
2.3 After the aluminum sheet plugs the holes, develops, pre-cures, and grinds the board, the board surface is soldered.
Use a CNC drilling machine to drill out the aluminum sheet that requires plug holes, make a screen plate, and install it on a shift screen printing machine for plug holes. The plug holes must be full, and both sides are preferably protruding. The process flow is: pre-treatment – plug hole – pre-baking – development – pre-curing – board surface solder mask
Because this process adopts plug-hole curing to ensure that the via hole will not lose oil or explode oil after HAL, but after HAL, it is difficult to completely solve the problem of tin bead in the via hole and tin on the via hole, so many customers do not accept it.
2.4 The solder mask on the board surface and the plug hole are completed at the same time.
This method uses 36T (43T) screen mesh, which is installed on the screen printing machine, using a backing plate or a nail bed, and plugging all the via holes while completing the PCB board surface. The process flow is: pretreatment–screen printing- -Pre-bake–Exposure–Development–Cure.
This process has a short time and a high utilization rate of equipment, which can ensure that the via holes will not lose oil and the via holes will not be tinned after hot air leveling. , The air expands and breaks through the solder mask, causing voids and unevenness. There will be a small amount of via holes hidden in tin during hot air leveling. At present, our company has basically solved the hole and unevenness of the via hole after a lot of experiments, choosing different types of ink and viscosity, adjusting the pressure of silk screen printing, etc., and this process has been adopted for mass production.
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