The via hole plays the role of interconnection and conduction of the lines. The development of the electronics industry promotes the development of the PCB, and the plug hole technology emerges as the times require. In order to meet the requirements of customers, there are many kinds of via hole plugging processes, the process flow is very long, and the process control is difficult. So, how is the PCB circuit board via hole plugging process realized? Let's find out with the editor below;
一. Plug hole process after hot air leveling
The process flow is: board surface solder mask → HAL → plug hole-curing. The non-plug hole process is used for production, and the aluminum sheet screen or ink blocking screen is used to complete the plug holes of all the fortresses after hot air leveling. The plugging ink can be photosensitive ink or thermosetting ink. This process can ensure that the via hole does not drop oil after the hot air is leveled, but it is easy to cause the plug hole ink to contaminate the board surface, and the unevenness may easily cause false soldering during placement.
二. Front plug hole process of hot air leveling
1. Use aluminum sheets to plug holes, solidify, and grind the board to transfer graphics
This process uses a CNC drilling machine to drill out the aluminum sheet that needs to be plugged into a screen to make a plug hole; the plug hole ink can also be thermosetting ink, which has high hardness and good bonding force with the hole wall. The process flow is: pre-treatment → plug hole → grinding plate → graphic transfer → etching → solder mask on the board surface
This method can ensure that the plug hole of the via hole is flat, the hot air is leveled, and there will be no quality problems such as oil explosion and oil drop at the edge of the hole. However, this process requires one-time thickening of copper, so the requirements for copper plating on the entire board are very high.
2. After plugging the hole with aluminum sheet, directly screen the solder mask on the surface of the board
This process uses a CNC drilling machine to drill out the aluminum sheet that needs to be plugged to make a screen, install it on the screen printing machine for plugging, and stop it for no more than 30 minutes after completing the plugging, and use a 36T screen to directly screen the solder on the surface of the board; process The process is: pre-treatment - plugging - silk screen - pre-baking - exposure - development - curing.
This process can ensure that the oil on the cover of the via hole is good, the plug hole is flat, and after hot air leveling, it can ensure that the via hole is not tinned and no tin beads are hidden in the hole, but it is easy to cause the ink in the hole to be on the pad after curing, resulting in solderability Bad sex.
3. Aluminum plate plug hole, developing, pre-curing, and grinding the plate, then carry out solder masking on the plate surface
Use a CNC drilling machine to drill out the aluminum sheet that requires plug holes, make a screen, and install it on a shift screen printing machine for plug holes; the plug holes must be full and protrude on both sides, and then cured, and the plate is ground for surface treatment. The process flow is: pre-treatment - plug hole - pre-baking - development - pre-curing - board surface solder mask.
This process adopts plug-hole curing, which can ensure that the via holes after HAL will not drop oil or explode; however, after HAL, it is difficult to completely solve the hidden tin beads in the via holes and the tin on the via holes.
4. Soldering and plugging of the board surface are completed at the same time
This method uses a 36T (43T) screen, installed on the screen printing machine, using a backing plate or a bed of nails, and plugging all the via holes while completing the board surface; the process flow is: pretreatment--screen printing- - Prebaking - Exposure - Development - Curing.
This process takes a short time, and the utilization rate of the equipment is high. It can ensure that the via hole does not drop oil and the via hole is not filled with tin after hot air leveling. , the air expands and breaks through the solder mask, causing voids and unevenness.
