PCB through hole plating step

1. PCB surface treatment: After the PCB is completed, there will be residual copper foil burr on the surface of the PCB attached to the surface of the through hole. At this time, there will be a rough feeling on the surface of the board by hand; these burrs will affect the plating quality, so it must be removed. The PCB surface treatment steps are as follows:


(1) Use a 400-mesh fine sandpaper or steel wool to perform a comprehensive back-and-forth brush on the surface of the PCB until the surface of the PCB is smooth.

(2) Place the PCB under the light source to check whether there is a hole plugged. If there is, use empty compressed air to spray out the hole to prevent the hole from being plugged and not turned on after plating. (If there is no compressed air, the bit can be removed with a bit smaller than the hole diameter.)


Second, silver glue through the hole:

Since the hole wall after drilling the substrate is not electrically conductive, the plating cannot be directly performed. Therefore, the step of filling the silver through the through hole is first performed, so that the silver glue is attached to the hole wall to perform plating in the through hole; the steps of filling the silver through the through hole are as follows :

1. Since the silver gel will precipitate after standing, it needs to be shaken evenly before use to facilitate the next step.


2. Pick up the PCB to make it approximately 30 with the desktop. On the upper side, a silver squeegee is applied to the holed area of the plate surface by a scraper (a strip size of about 10 cm × 5 cm, which can be cut by a substrate edge material), and the silver glue is scraped into the hole, and the other side is finished.


※Please confirm whether the silver glue is scraped into the hole as follows:

(1) When the scraper passes through the hole, it can be seen that there is a silver film in the hole, which means that the silver glue has been poured into the hole.

(2) When the entire surface of the board is completed, check the PCB to see if all the holes have silver glue overflowing the edge of the hole. If there is, continue to work on the other side of the hole. The operation method is the same as above.


3. Use compressed air to blow out the silver glue stuck in the hole, leaving only a proper amount of silver glue attached to the hole wall. (Note that the air pressure is not too high to prevent all the silver glue from being blown out; if the equipment without compressed air can be sucked out by the vacuum cleaner, the same effect can be achieved).


4. Take the cleaning rag to remove the excess silver glue on the board surface, and wipe off the excess silver glue as much as possible to avoid the silver glue becoming harder after the drying step below.

※If you use toilet paper or the like without a rag, you must make sure that the peeled fibers do not plug the holes, if any, you can remove them with a thin wire.


5. Check if there is silver glue on the wall of each hole, and there is no excess silver glue to plug the hole. If it is found that the hole is plugged with silver glue, remove it with a thin wire.

※When there is silver glue on the wall of the hole, the PCB can be placed in a bright place to tilt the board slightly, so that the wall condition can be seen. If there is silver glue, the hole wall can be reflected.


6. Bake the PCB in the oven at a baking temperature of 110 ° C and a baking time of 15 minutes. The purpose of baking is to make the silver glue harden and adhere to the hole wall. The oven can be used in general household type. This step involves the adhesion of copper in the hole is very important. After the end, the PCB is taken out of the oven and let it be Cool at room temperature.


7. Use 400 mesh fine sandpaper or steel wool to perform a comprehensive back-and-forth brush on the surface of the PCB to remove the hardened silver paste from the PCB surface until the surface of the PCB is smooth. The baked PCB is brown. The conductive ink hardened on the surface of the PCB is removed by fine sandpaper or steel wool. The surface of the cleaned PCB should have the metallic luster of copper. If the silver paste on the surface is not removed, after plating The adhesion of the surface-plated copper is poor, and there may be cases where the copper surface is peeled off or the surface is uneven, and special care is required.


Third, PCB plating:

1. Dip the PCB into the water tank or directly flush it to make it fully wet in the hole wall. After wetting, pay attention to the air bubbles in the hole wall. If there are air bubbles, remove it with water.


2. Place the PCB in the plating bath and swing the handheld PCB back and forth in the slot (about 10 times) so that the hole wall is completely wetted by the plating solution.


3. Use a dovetail clamp to fix it in the center of the slot. Take the A4 size PCB as an example. The plating current is 3.5A and the plating time is 60 minutes.


※ In order to obtain better plating quality, it is best to place the board in the center of the plating tank, and the cathode alligator clip (black) is sandwiched in the center of the crossbar, so that the concentration of plating solution and the plating current can be evenly distributed. To the various parts of the PCB, and get better plating quality.

4. PCB plating current setting ratio It is recommended to set the current according to the size of the PCB.


5. After the plating is completed, remove the PCB, rinse it with water, and blow dry to avoid oxidation of the PCB surface.


6. After the electroplating is completed, use 400-mesh fine sandpaper or steel wool to perform a comprehensive back-and-forth rubbing on the surface of the PCB until the surface of the PCB is smooth, to flatten the bumps and depressions generated during plating to avoid errors in the plane detection during PCB engraving.


7. Move the board to the PCB engraving machine for line production