PCB Tech - Circuit board through hole plating step description

1. Circuit board merchant surface treatment:

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 plating quality and must be removed; the surface of the circuit board The processing steps are as follows:

(1) Use 400-mesh sandpaper or steel wool to scrub the surface of the circuit board roundly until the surface of the circuit board is smooth.
(2) Put the circuit board under the light source to check whether the holes are blocked. If so, use compressed air to spray out the impurities in the holes to prevent the holes from being blocked and not conducting after plating. (If there is no compressed air, a drill bit smaller than the hole diameter can be used to remove debris

2. Silver glue through hole:

Since the hole wall after the substrate is drilled is not conductive and cannot be electroplated directly, it is necessary to carry out the step of through-hole silver filling first, so that the silver glue is attached to the hole wall 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 being left standing, it must be shaken evenly before use to facilitate the next step.

2. Pick up the circuit board so that it is about 30 with the desktop. On top, use a spatula (long strip size of about 10cm * 5cm, which can be cut from the substrate edge material) soaked with silver glue and move it back and forth across the holed area of the board surface to scrape the silver glue into the hole. After one side is completed, move on 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, which means that the silver glue has been poured into the hole

(2) After the through holes are completed on the entire board surface, turn the circuit board over to check whether all the holes have silver glue overflowing the edges of the holes. If there are, continue the through hole operation on the other side. The operation method is the same as the 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 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, 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. Try to wipe the excess silver glue clean to avoid the silver glue hardening after the following drying steps and it takes more time to remove.

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 to plug the hole. If any hole is plugged by silver glue, remove it with a thin wire.

When checking whether there is silver glue on the wall of the hole, you can place the circuit board in a bright place and tilt the board slightly so that the condition of the hole wall can be seen. If there is silver glue adsorption, the reflection of the hole wall can be seen.

6. Put the circuit board into the oven and bake, the baking temperature is 110 degree Celsius, and 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 copper in the hole. It is very important. After the end, the circuit board is taken out of the oven and allowed to 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. The baked 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 a copper metallic luster; if the silver glue on the board surface is not removed, After electroplating, 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.

3, PCB circuit board plating:

1. Immerse the circuit board in a sink or flush it directly to make the hole wall fully wet. After wetting, pay attention to no bubbles in the hole wall. If there are bubbles, flush again to remove them.

2. Put the circuit board into the plating tank, hold the circuit board and swing it back and forth in the tank (about 10 times) to make the hole wall completely wetted by the plating 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 Each part of the circuit board can obtain better plating quality.

4. The circuit board plating current setting ratio is recommended to set the current according to the size of the circuit board.

5. Take out the circuit board after electroplating, rinse with clean water and blow dry 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 roundly until the surface of the circuit board is smooth, so as to level the bumps and dents 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