1. PCB Surface Treatment:
After the drilling is completed, there will be residual copper foil burrs on the surface of the PCB attached to the surface of the through holes. At this time, the surface of the board will be rough when touched by hand. These burrs will affect the plating quality, so they must be removed. The PCB surface treatment steps are as follows:
1.1 Use 400-mesh fine sandpaper or steel wool to brush back and forth on the surface of the PCB until the surface of the PCB is smooth.
1.2 Put the PCB under the light source to check whether the holes are plugged. If so, use compressed air to spray out the debris in the holes to prevent the holes from being plugged and not conducting after electroplating. If there is no compressed air, the debris can be removed with a drill bit slightly smaller than the hole diameter.
2. Silver Glue Through Hole:
Since the hole wall of the substrate after drilling is not conductive, it cannot be directly electroplated. Therefore, it is necessary to perform the step of pouring silver glue into the through hole first, so that the silver glue is attached to the hole wall for electroplating in the through hole. The steps of filling the through holes with silver glue are as follows:
2.1 Since the silver glue will precipitate after standing, it should be shaken evenly before use to facilitate the next step.
2.2 Pick up the PCB so that it is about 30 degrees from the desktop, use a scraper (strip size about 10cm×5cm, which can be cut from the edge of the substrate) to dip the silver glue and move it back and forth in the hole area of the board to remove the silver glue. Scrape into the hole and do the other side after one side is done.
*The method to confirm whether the silver glue is scraped into the hole is as follows:
(1) When the scraper passes through the hole, you can see a layer of silver glue film in the hole, which means that the silver glue has been poured into the hole.
(2) When the entire board surface is completed with through holes, turn the PCB over to check whether all the holes have silver glue overflowing the edge of the holes. If there are, continue the through hole operation on the other side. The operation method is the same as the above.
2.3 Use compressed air to blow out the silver glue plugged in the hole, leaving only an appropriate amount of silver glue attached to the hole wall. Note that the air pressure should not be too high to prevent all the silver glue from being blown out. If there is no compressed air equipment, a vacuum cleaner can be used to suck out the silver glue to achieve the same effect.
2.4 Use a cleaning rag to remove the excess silver glue on the board. Try to wipe the excess silver glue as much as possible to avoid the silver glue becoming hard after the following drying steps. It will take a long time to remove.
*If you use toilet paper or similar materials without a rag, make sure that the flaking fibers are not plugging the holes, and if there are, you can use a thin wire to remove them.
2.5 Check whether there is silver glue on the wall of each hole, and there is no excess silver glue to plug the hole. If any hole is found to be plugged by silver glue, use a thin wire to remove it.
*When checking whether there is silver glue on the hole wall, you can place the PCB in a bright place and tilt the board slightly, so you can see the hole wall condition. If there is silver glue adsorption, you can see the reflection of the hole wall.
2.6 Put the PCB into the oven to bake, the baking temperature is 110℃, and the baking time is 15 minutes. The purpose of baking is to make the silver glue really harden and adhere to the hole wall. The oven can be used as a general household type. This step involves the adhesion of the copper in the hole. It is very important. After the end, take the PCB out of the oven and let it cool at room temperature.
2.7 Use 400-grit sandpaper or steel wool to brush the surface of the PCB comprehensively to remove the hardened silver glue on the surface of the PCB until the surface of the PCB is smooth. The baked PCB is brown. Use fine sandpaper or steel wool to remove the conductive ink hardened on the surface of the PCB. The surface of the PCB after removal should have the metallic luster of copper; The adhesion of electroplated copper on the surface is poor, and the copper surface may peel off or the surface may be uneven, so special attention should be paid to it.
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