The process of PCB from light board to show circuit pattern is a more complex process of physical and chemical reaction. As etching is a very important finishing step of PCB manufacturing, we will analyze etching in this passage.

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At present, the typical process of PCB is pattern plating etch process which means in the outer layer of the board to retain the copper foil part. That is, the graphic part of the circuit is pre-plated with a layer of tin lead corrosion layer. The remaining copper foil is then chemically etched away. The whole process is known as etching.

In this article, we will provide you PCB minimum etch techniques. If you are interested in the PCB etching, please check and read the content below for more information.

What are the main types of PCB etch?

What are the 5 tips of PCB minimum etch technique in design?

1.Getting to know the definition of PCB minimum etch

Even if you’ve never fabricated a PCB, you might be familiar with the process. PCB etching involves the application of UV-resistant laminate to a pre-sensitized photoresist copper layer, which is then exposed to UV rays. Areas that are not covered will be etched off in a special etching solution.

The PCB minimum etch technique has more to do with what happens at the design stage than the process of PCB etching itself. It refers to the idea of keeping as much copper area on the PCB as possible. Effectively, what minimum etch does is impose a tradeoff - it improves heat dissipation, while making parasitic capacitance more prominent.

2.The main types of PCB etching

Before the PCB etching, we should know the types of etching so that we could make out the difference of them. There are two layers of copper on the board when etched. In the outer layer of the etching process, only one layer of copper must be etched away, and the rest will form the final desired circuit.

Another method is the entire board is copper, photosensitive film outside the part is only tin or lead tin resist layer. This process is called “full board copper plating”. Compared with the graphics plating, the biggest drawback of the whole board copper plating is plated twice the copper surface and the etching must also be corroded them. So when the wire width is very fine will produce a series of problems.

3.Process the PCB wet etching

Wet etching is a technique in which etching materials are immersed in an etching solution for etching. It is the most common etching method. There are three factors that affect the etching rate of the etched object: etching solution concentration, etching solution temperature, and stirring. Qualitatively speaking, increasing the etching temperature and adding stirring can effectively increase the etching rate; The characteristic of wet etching is isotropic.

Advantages of wet etching

· Good surface uniformity.

· Good adaptability, suitable for almost all metals, glass, plastics, etc.

· Low cost.

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· With excellent selectivity, the current film will stop after etching without damaging the film of other materials below.

4.Process the mechanical etching

In response to the inexorable tightening of environmental regulations and the difficulty of obtaining strong acids and oxidizers in many locales, "mechanical etching" has seen unprecedented growth over the last 10 years. In spite of high up-front costs and lack of plated through-holes, its complete freedom from toxic chemicals has made this technique very attractive to many PCB prototyping shops.

As the density and complexity of circuit designs have increased, forming reliable electrical connectivity between the top (component) and bottom (solder) circuit patterns has evolved from a mere convenience to an absolute necessity. While some mechanical etch vendors offer manual and semi-automatic machines for inserting eyelets into all of the designated through-holes, the cost of the equipment, the penalty in PCB real-estate, and the relative sluggishness of the process render it undesirable for many applications. As a result, many shops have adopted simplified electrolytic plating processes to accomplish this critical task.

5.Optimize the PCB minimum etch technique

There are bound to be uncovered areas on a PCB if you’re not taking proactive steps to optimize it with PCB minimum etch technique. Thankfully, it’s quite easy to ensure that you’re leaving as much copper area on the finished PCB as possible.

First, you’ll need to create a copper pour for the ground plane. Then, look for areas that are left out in the copper pour. Usually, these areas are not connected to the ground net. You’ll need to manually create a ground net in the area by using vias or by adjusting nearby traces to make space for a ground connection. Once that’s done, repour the ground plane.

By now, you ought to have a copper plane that’s covering most of the surfaces. There shouldn’t be any odd areas that are left uncovered. Finally, run a DRC check to ensure that all the segments of ground planes are connected.

March 13,

The Chemical Connection: Wet Process Start-up Considerations

Are you (or your company) considering starting your own PCB fabrication process? After the most recent IPC APEX EXPO, maybe you’ve made connections to help you with your start-up, but do you have a solid game plan? If you are new to managing a PCB shop, the first thing to know is that wet processing is essential in making PCBs. Wet processing steps, such as cleaning, developing, etching, and stripping, are among the many steps in the PCB fabrication process that require thorough planning. When you are just starting to get involved in this industry, keeping track of all this can feel overwhelming. If you fit in this category, it’s best to start with the basics and work your way up. Here are a few considerations and base essentials to aid you in starting up the wet processes for your new facility.

Scale of Production
Before you start planning out how you want your PCB shop to function, you will need to lay out your goals. For instance, it’s important to know the type of circuit boards you plan to make, as well as how many you want to make and how quickly you want to produce them. Knowing this information is vital because it will drastically shape your manufacturing process. Depending on your products, you may have to utilize different photoresists and wet processing chemicals (i.e., different cleaning, developing, etching, and stripping solutions).

In addition, you need to know the scale of your production so you can ensure that you get the suitable equipment for your level of manufacturing. For example, if you are planning to run a facility with a large output of panels per day, a multi-chambered etch machine may be something to consider (Figure 1). This is because the longer the etch chamber, the faster you can run the conveyor speed while maintaining the same processing time. This increased conveyor speed with a larger etch chamber means that more panels can be inside the etch chamber at the same time. Keep in mind that a larger machine also means that it will take up more floor space; the trade-off for increasing production is committing to a capital investment and sacrificing some space.

Utilities
When you are planning to start a PCB shop, you need to consider not only what equipment you’ll need, but also the basic utilities required and how those will be connected. The primary utilities/base necessities are electricity, water, and ventilation. Typically, utilities run 15–20% of equipment cost. Although these utilities are a necessity for any manufacturing facility, some situations may need additional considerations. For instance, when it comes to your electrical needs, not only do you have to ensure you get the power you need to run the equipment, but you need to consider where electrical cabinets should be located. If you are utilizing an alkaline etcher, you’ll need something to help regulate the airflow through the machine to ensure optimal etching.

Available Workspace
As I mentioned, the floor space requirements of your equipment should be a major consideration when planning your facility. When deciding on the equipment you need to meet production goals, you must find a balance between available floor space and how to meet your production needs. When working on the layout of your facility, keep in mind that you’ll need to reserve additional space to ensure that people can easily run and maintain your equipment. Poor manufacturing floor design can create inconvenient situations for operation and maintenance, which can negatively impact the longevity and efficiency of your equipment. Having an awareness of space is vital when planning your process because you need a layout that will get your equipment inside the facility and leave enough space for it to be operated efficiently.

Process Locations
When planning out your wet process, you may want to consider its location relative to other equipment. This is because corrosion is a given with etching equipment. Although the equipment safely contains the etching chemicals, the process tends to create a corrosive environment; anything metal in the area that lacks some form of corrosion resistance will experience corrosion over time. Etching equipment is often kept in its own room to account for this phenomenon. Therefore, if you have an expensive machine testing your printed circuit boards, you do not want it in the same room as your etching machine.

Waste Management
Producing PCBs generates many different forms of waste. For wet processing, contaminated rinse water and excess etchant are common waste streams. As you process a panel through one of the wet processes, it’s normal to rinse it before it goes to the downstream processes. These rinse waters become contaminated with wet processing chemicals and need to be treated before disposal. This is something that you can do in-house, but how you do it may depend on the wastewater regulations in your area. You may be required to precipitate any heavy metals out of the water to make it meet your discharge permit limits. In this case, the precipitated metal sludge is another waste steam that will need to be handled. Typically, this sludge is filtered off from the water, dried, drummed, and sent off to a waste treatment facility.

Excess etchant is another waste product you need to plan for. As you etch your PCBs and make chemistry adjustments, you will accumulate etchant in your etching machine over time. This excess etchant needs to be pumped out before the level gets too high in your etcher bath. Since the excess etchant usually doesn’t meet quality requirements for reuse, and because it is concentrated, it is common practice to pump the excess etchant into a barrel that will get shipped to a waste treatment facility.

Conclusion
If you are looking for a good place to start planning your PCB fabrication process, I hope the information I’ve provided here gives you a better idea of what to expect. Knowing about these matters and preparing for them ahead of time can make planning your wet process—and your job—much easier.

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