One crucial step in the manufacture of PCBs is PCB etching. The intended circuit layout must be revealed by eliminating copper out from the PCB’s surface. All copper on the PCB is removed during the etching process, with the exception of the circuitry which is tin-plated for protection. Its copper is then cleaned once the tin has been extracted.
Though it seems simple, the etched circuit board process is highly intricate, and accuracy is crucial. Also, a variety of Circuit board etching techniques can be used, and each one has advantages and disadvantages of its own. We’ve created this tutorial to give you more information on the circuit board etching procedure.
What Does Etched Circuit Board Mean?
A circuit board’s undesirable copper is eliminated through the process of Circuit board etching. Only the necessary circuit is left on the PCB after all of the extra copper has already been taken off. The circuit board’s layout is prepared prior to the start of the etching procedure. Photolithography is the method used to put the desired board layout onto the PCB. This serves as the pattern for selecting the copper pieces that must be taken off the board.
Tin plating serves as an etch resist on the PCB’s outer layer. This etch resist is the photoresist in the internal layer, though. In general, there exists two methods for etching the outer and inner layers of a PCB. These include wet etching and dry etching.
The Dry Etching Process
In order to start chemical interactions between the laminate’s surface atoms and base, dry etching typically requires plasma. The undesirable copper dissolves as a result. Although plasma has been frequently used during dry etching, lasers can also be used.
Plasma etching
Since 1960s, this has existed. It didn’t become well-known, though, until about the 1970s. This method was developed to assist manufacturers dispose of liquid waste more sparingly while still achieving selectivities which were challenging to accomplish using wet chemistry.
During plasma etching, the PCB is exposed to high-speed glow discharge stream from a proper gas mixture. Hence, plasma etching can be described as a dry, clean procedure that doesn’t need any chemicals.
Moreover, plasma etching has the ability to do precise and controlled small scale etching. It’s also quite popular since it makes it less likely that solvents will penetrate into vias or that they will get contaminated.
Plasma etching, despite its benefits, is exceedingly expensive. Due to this, it will probably be significantly more costly than the wet etching process unless you consistently etch large quantities of material.
Laser etching
Utilization of precision, computer-controlled hardware is made possible by laser etching. A powerful laser is used to create trace lines upon that PCB’s substrate during the procedure. These undesirable copper wires either disappear completely or flake off the printed circuit board.
As one of its key advantages, laser etching reduces the amount of steps involved in the whole process. Also, it does away with the usage of any harmful chemicals, acids, or inks.
Large boards can be challenging to etch them evenly, and residues and etchant might be challenging to remove if they wouldn’t completely evaporate. Also, the procedure for laser etching is quite expensive, just like plasma etching.
Wet etching
Unwanted copper is removed during the process of wet etching using a solution which undergoes chemical reactions. Acidic chemicals or alkaline chemicals could be employed for the process, depending upon that etches substance.
Acidic etching
Here, the rigid PCB’s inner layers are typically removed using the acidic approach. Either ferric chloride or cupric chloride is employed in this method. The more popular of both, cupric chloride, precisely removes tiny features while offering a steady etch rate as well as continual regeneration.
As the acid will not really react with photoresist or harm the necessary component, the acidic technique is typically employed for the innermost layer. Moreover, the undercuts, which is described as the etched material’s lateral erosion beneath the shield of tin/lead—are minimized. Yet, compared to alkaline etching, the acidic etching may be a time-consuming operation. Due to this, it isn’t usually appropriate for significant numbers of Circuit boards.
Alkaline etching
Circuit board’s outer layers are frequently removed using the alkaline technique. Also, this is how we operate. A PCB can be quickly and affordably etched using alkaline etching. The procedure must be constantly monitored, though. This is due to the fact that prolonged contact with the solvent may cause harm to the board.
Alkaline etching can often be done in a high-pressure, conveyorized spray chamber that makes the entire process as fast, efficient, and precise as possible. The Circuit board is subjected to a fresh etchant inside the chamber.
The breakpoint refers to the stage of the etching when all of the undesirable copper has been removed. Typically, this is accomplished at the spray chamber’s halfway.
Parameters that Impact the Etched Circuit Board Process
The etch rate you acquire is influenced by both the etched time and the etching solution’s composition. By regulating specific parameters, the process of etching can be made to be of high quality. Let’s think about them
Temperature
Remember that most etching machines would be made of plastic components because such metallic parts have become reactive to etchants when adjusting the solution’s temperature. The temperature must not be extremely high if the plastic parts on the etching machine are plastic. The optimal temperature range in this case is between 50 and 55 degrees Celsius, or 122 to 131 degrees Fahrenheit.
Unique Gravity
The etchant’s concentration was associated with specific gravity. Typically, a larger number corresponds to a greater etch rate. For the alkaline etching, the parameter becomes particularly significant when focusing on the solution’s pH. When the solution’s pH varies from 7.9 to 8.1, alkaline etching could be done successfully.
pH
When the solution’s pH is below 8.0, there may have been insufficient ammonia or excessive ventilation that caused the pH to decrease. Remember that when a pH is greater than 8.8, the etching rate could be low. Whereas if the etchant has absorbed water or contains an excessive amount of copper, this problem may arise. Any rise in pH levels could lead to inaccurate readings being acquired for the acidic etching.
Since the harsh plating solutions might harm electrodes not suited for the plating applications, pH monitoring in the plating solutions could be challenging. Many plating applications call for the Sensorex pH Electrode, which is built to tolerate harsh circumstances.
Concentration of the Chemical Additive
The etching rate can be efficiently increased by using chemical additives. Hydrochloric acid is the most widely utilized addition because it can improve an etchant’s capacity to cling to dissolved metals. Chemical additives have been required when a manufacturing or industrial facility needs constant etching. Even when additions complicate etchants, its etching rate will always increase.
Possibility for Oxidation-Reduction
The oxidation and reduction potential that describes how active this etchant is, is the final and fifth parameter. The ORP immediately reveals the relationship between cupric and cuprous ions as well as how these ferric ions can relate to the ferrous ions.
The etchant’s initial cupric or ferric state will shift to a ferrous or cuprous condition when the copper has been etched.
You could be sure that the etching rate is high if you measure the ORP to be high. The low ORP levels indicate a less effective etchant. The temperature of the etchant and the content of the free acid can both be used to calculate a solution’s ORP value. It is feasible to convert these cuprous ions back to the cupric form by adding an oxidizer as well as a free acid into the etchant.
What Phase of the production process is the Etched Circuit Board At?
Near the conclusion of the process of circuit board manufacturing is the circuit board etching procedure. Although the actual PCB fabrication process is challenging, we have simplified it.
The etching procedure can start after the Circuit has been tin-plated, which helps safeguard the board. Here, the board is run through a conveyorized PCB etching equipment, that sprays it using a amonicon solution, to etch the area surrounding the traces. This eliminates any exposed copper on the circuit board’s surface that is not covered by tin plating, retaining just a covered tracking.
The board is dried as well as thoroughly examined after the etched circuit board procedure. It is subsequently run through the tin-stripping machine. The tin covering the residual copper traces is removed by this machine using nitric acid.
The etched circuit board process is finished at this point, and the circuit board can move on to the production phase.
Conclusion
Etched circuit board has to do with the elimination of any undesirable copper present in any circuit board through the process of Circuit board etching. Only the necessary circuit is left on the PCB after all of the extra copper has already been taken off. The circuit board’s layout is prepared prior to the start of the etching procedure.
