Step-by-step analysis of PCB through hole plating

by:A-TECH      2021-04-01
1. Surface treatment of the electric board: After the circuit board is drilled, there will be residual copper foil burrs on the surface of the circuit board attached to the surface of the through hole. At this time, the surface of the board will be rough when touched by hand; these burrs will affect the quality of electroplating. Therefore, it must be removed; the circuit board surface treatment steps are as follows: (1) Use 400-mesh sandpaper or steel wool to scrub the surface of the circuit board roundly until the circuit board surface is smooth. (2) Put the circuit board under the light source to check whether the hole is blocked. If so, use compressed air to spray out the debris in the hole to prevent the hole from being blocked and not conducting after electroplating. (If there is no compressed air, a drill bit smaller than the hole diameter can be used to remove debris. Second, silver glue through hole: Since the hole wall after the substrate is drilled is not conductive, electroplating cannot be directly carried out, so the through hole silver glue is required first The steps of making the silver glue adhere to the wall of the hole for electroplating in the through hole; the steps of the through-hole silver filling glue are as follows: 1. Since the silver glue will precipitate after standing, it must be shaken evenly before use. Use it in the next step. 2. Pick up the circuit board so that it is about 30° from the desktop, and place it on the board surface with a scraper (long strip size of about 10cm×5cm, which can be cut from the substrate edge material). Move the holed area back and forth to scrape the silver glue into the hole. After one side is completed, proceed to the other side. ※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 that there is a layer of silver glue film in the hole. That means that the silver glue has been poured into the hole (2) When the entire board surface has completed the through hole, turn the circuit board over to check whether all the holes have silver glue overflowing the edge of the hole, if there is, continue to the other side Through hole operation, the operation method is the same as above. 3 Use compressed air to blow out the silver glue plugged in the hole, leaving only a proper amount of silver glue attached to the wall of the hole. (Note that the air pressure should not be too large to prevent all the silver glue from being Blow out; if there is no compressed air equipment, the silver glue can be sucked out by a vacuum cleaner to achieve the same effect). 4 Take a cleaning rag to remove the excess silver glue on the board, and try to wipe the excess silver glue to avoid the following drying steps. It takes more time to remove the silver glue to harden. ※If you use toilet paper or the like without a rag, you must make sure that the peeled fiber does not plug the hole. If there is, you can use a thin wire to remove it. 5. Check whether there is silver glue on the wall of each hole, and there is no excess silver glue plugging the hole. If a hole is plugged by silver glue, remove it with a thin wire. ※Check whether there is silver glue on the hole wall. Place the circuit board in a bright place and tilt the board slightly so that you can see the condition of the hole wall. If there is silver glue adsorption, you can see the reflection of the hole wall. 6. Put the circuit board in an oven and bake at a temperature of 110°C. The baking time is 15 minutes. The purpose of baking is to make the silver glue harden and adhere to the wall of the hole. The oven can be a general household type. This step involves the adhesion of the copper in the hole. Take it out of the oven and let it cool at room temperature. 7. Use 400-mesh sandpaper or steel wool to scrub the surface of the circuit board roundly to remove the hardened silver glue on the surface of the circuit board until the surface of the circuit board is smooth. Bake it. The circuit board is brown. Use fine sandpaper or steel wool to remove the conductive ink that has hardened on the surface of the circuit board. The surface of the circuit board after removal should have copper metallic luster; if the silver glue on the board surface is not removed, electroplating The adhesion of electroplated copper on the back surface is poor, and there may be peeling of the copper surface or uneven surface, which requires special attention. 3. Circuit board electroplating: 1. Immerse the circuit board in a sink or flush it directly to make holes The wall can be fully wetted. After wetting, pay attention that there should be no bubbles in the hole wall. If there are bubbles, flush water to remove them. 2. Put the circuit board into the electroplating tank, and hold the circuit board back and forth in the tank Swing (about 10 times) to make the hole wall It is completely wetted by the electroplating solution. 3. Use a dovetail clip to fix it in the center of the slot. Take the A4 size circuit board as an example. The electroplating current is 3.5A and the electroplating time is 60 minutes. ※In order to obtain better electroplating quality, it is best to place the board in the center of the electroplating tank, and the alligator clip (black) of the cathode is clamped in the center of the crossbar, so that the concentration of the electroplating solution and the electroplating current can be evenly distributed To all parts of the circuit board, to get better plating quality. 4. The circuit board electroplating current setting ratio is recommended to set the current according to the size of the circuit board. The setting conditions are as follows: 5. After the electroplating is completed, the circuit board is taken out, rinsed with water and dried to avoid oxidation of the circuit board surface. 6. After electroplating is completed, use 400-mesh sandpaper or steel wool to scrub the surface of the circuit board comprehensively until the surface of the circuit board is smooth, so as to level the bumps and depressions generated during electroplating to avoid plane detection when the circuit board is engraved. Produce errors. 7. Move the board to the circuit board engraving machine for circuit production
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