Printed circuit boardEtching is a very important process, and there will be many problems during the etching process. This chapter mainly explains the common problems encountered in PCB etching, as well as fast and effective solutions!

1. Reduce side erosion and protrusion, and improve etching coefficient

The side erosion of printed circuit board produces sharp edges. Generally, the longer the printed circuit board is processed in the etching solution, the more serious the side erosion is. The side erosion of pcb seriously affects the precision of printed wire. Serious side erosion will make it impossible to manufacture fine wire. When the side erosion and edge decrease, the etching coefficient increases. A high etching coefficient indicates the ability to adhere to thin wires, making the etched wires close to the original size. Whether it is tin lead alloy, tin, tin nickel alloy or nickel, excessive protrusion of electroplating etching resist will constitute short circuit of wire. As the sharp edge is easy to break, it forms an electrical bridge between two points of the conductor.

There are many factors that affect the side erosion of printed circuit boards. Here are some examples:

1) Etching method: immersion and bubble etching will form larger side etching, while splash and spray etching will have smaller side etching, especially spray etching.

2) Etching solution type: different chemical components of different etching solutions lead to different etching rates and etching coefficients

3) Etching rate: slow etching rate will cause serious side etching, and the improvement of etching quality is closely related to the acceleration of etching rate. The faster the etching speed is, the shorter the time the plate stays in the etching solution, the smaller the amount of side etching, and the clearer and uniform etched pattern.

4) PH value of etching solution: When the PH value of alkaline etching solution is high, the side etching increases.

5) Copper foil thickness: to achieve the etching of thin wires with minimum side erosion, it is better to use (ultra) thin copper foil. The thinner the wire width, the thinner the copper foil thickness.

2. Improve the divergence of etching rate between printed circuit boards. In continuous board etching, the more divergent the etching rate is, the more evenly etched boards can be obtained. To reach this request, it is necessary to ensure that the etching solution continuously adheres to the optimal etching state throughout the entire process of etching, and plead for choosing the etching solution that is easy to regenerate and compensate, and the etching rate is easy to control. The process and equipment that can provide constant operating conditions and automatically control various solution parameters shall be selected and completed by controlling the amount of copper dissolved, PH value, concentration of solution, temperature, uniformity of solution flow (spray system or nozzle and swing of nozzle), etc.

3. The uniformity of the etching rate of the whole board surface is high. The etching uniformity of the upper and lower sides of the board and all parts of the board surface is determined by the uniformity of the etchant flow on the board surface. During the etching process of the printed circuit board, the etching rates of the upper and lower boards are often different, and the etching rate of the lower board is higher than that of the upper board. Due to the accumulation of solution on the upper plate surface, the interruption of etching response is weakened. The uneven etching of upper and lower plate surfaces can be handled by adjusting the spraying pressure of upper and lower nozzles. A common problem in etching and printing plates is that it is difficult to make all the plates etched clean at the same time. The edge of the plate etches faster than the center of the plate. It is an effective measure to adopt a spraying system and swing the nozzle. Further improvement can be achieved by making the spraying pressure at the center and edge of the plate different, and by intermittently etching the front edge and rear end of the plate, so as to reach the etching uniformity of the entire plate surface.

4. Improve the ability to safely dispose and etch harsh copper foils and thin laminates. When etching thin laminates such as the inner layer of multilayer boards, the boards are easy to be wound on rollers and transfer wheels to form waste products. The equipment for etching inner laminates must ensure that thin laminates can be disposed stably and reliably. Many equipment manufacturers attach gears or rollers to the etching machine to prevent such phenomena, A better method is to use the additional left and right swaying Teflon coated wire as the support for the transfer of thin laminates. For the etching of thin copper foil (such as 1/2 or 1/4 oz), it is necessary to ensure that it is not scratched or scratched. Thin copper foil cannot withstand the mechanical disadvantages such as etching 1 oz copper foil. Sometimes, even violent vibration may scratch the copper foil.

5. Reduce pollution. Copper's pollution to water is a common problem in printed circuit consumption, which is aggravated by the use of ammonia alkali etching solution. As copper is complexed with ammonia, it is not easy to remove it by ion exchange method or alkali precipitation method. The method of second spraying operation is used to rinse the plates with copper free additive solution, greatly reducing the amount of copper discharged. The excess solution on the plates is removed by air knife before water rinsing, thus reducing the rinsing burden of water on copper and etched salts.