Chemical etching ties into many different industries. Automotive, aerospace, medical, semiconductor solar, electronics, and many more industries produce products by chemical etching. You are probably using something that was produced by chemical etching right now. This is why the photochemical machining (PCM) industry is so versatile. Whenever this industry innovates and grows, so does the technology it feeds into. In the 1950s, chemical etching revolutionized printed circuit boards by providing an efficient, economical method to produce reliable electronics. How could chemical etching revolutionize technology again, and what changes should we expect in chemical etching? In this article, we will talk about the 5 areas in chemical etching where we can expect innovation.
1. Process Simplification
There is always room for improvement when it comes to simplifying process equipment. The more accessible the equipment becomes; the less hassle preventive maintenance and operation becomes. Etching can be a simple process, but when you are using it to commercially produce parts or circuits, more constraints and challenges come along and lead to more complex systems. A simplistic design that gets the job done can go a long way.
2. High Resolution
Obtaining higher resolution means being able to produce more precise and complex designs. With etching finer features, comes the challenges of consistently meeting narrow tolerances. Many of the limiting factors to high-resolution etching occur prior to the etching process. It is critical that items such as proper artwork compensation, thickness and consistency of photo-resist application, precise alignment of the top and bottom side artwork, and the resolution and capability of the imaging equipment all be optimized to achieve high-resolution etch results. Even something as small as a speck of dust can result in a reduction of the resolution of the etched part. Clean rooms rated class 10,000 or better are required.
3. Undercut
With the trend of designs becoming more complex and packed together, Undercut has become an issue that limits resolution as you increase etch depth. If undercut was completely eliminated, you could theoretically obtain a feature of any size with any etch depth. The main problem with undercut is that it is desirable to have a fast etch rate to maximize production. However, the typical trend is that whatever results in higher etch rates, also results in more undercut.
Some etchants have been used to try to reduce sidewall etching by forming a complex with the sidewalls, but it still has not gotten rid of the issue of undercut. Sidewall etching can also be reduced by controlling the crystalline structure of the metal. Controlling this is aspect however can be an expensive and challenging process. In the near future, It is entirely possible a new form of etchant or method to control crystalline structure can come about to efficiently reduce undercut.
4. Etch Uniformity
Etch uniformity is also another area in chemical etching that can cause growth. As manufacturers try to maximize production, there will be a shift towards using larger panels to get more parts per panel. However the larger the panel, the harder it is to maintain a uniform etch. This difficulty in etch uniformity comes from what is called "The Puddle Effect".
This effect describes the lack of diffusion on the surface of the panel due to the formation of a puddle in the middle. The puddle inhibits a uniform reaction by creating a barrier between the fresh etchant and the surface. Because of The Puddle Effect, the edges of panels etch faster than the middle. This tends to be less of a problem in chemical milling because you etch through. Uniformity in the printed circuit board industry, however, can more challenging to achieve.
There have been many attempts to overcome this problem, but the best solution currently is "intermittent spray". This is a solution developed by Chemcut to overcome the deviation caused by The Puddle Effect. It is considered the best because it minimizes deviation without any loss in production rate, transport capabilities, and equipment simplicity. Intermittent spray achieves this by creating a targeted etch in the middle of the panel to compensate for the difference on edges.
5. Thin Material Transport
In the printed circuit board industry, there is always a drive to obtain thinner, flexible material.
Transporting thin material is a challenge in chemical etching. This is because the panels need enough open space to be sprayed with the etchant. The downside here is that when there is open space, there is a chance for the leading edges to deviate and cause wrinkles and folds. There is a balance that needs to be met because as you fill the conveyor with transporting aids, you lose etching efficiency. That is because it becomes harder for the etchant to reach the surface. Not only do you lose efficiency, but you also have to worry about etch rates differing on the top and bottom.
A common approach to solving this problem is to attach a thicker board, known as a leader, to the leading edge of the thin material. This prevents the front end from getting caught anywhere in the line. The problem with this method is that it inhibits production rates and requires someone to manually attach and remove leaders. This is why many people in the chemical etching industry seek thin material transport systems that do not require leaders.
Due to the wide variety of thin materials and substrates that are currently available, it is not practical to rigidly define the thinnest material that etching equipment can transport without leaders. A general guideline for minimum thickness is less than 1 mil (.001 inch, or 25 micron). It is recommended that materials below this guideline be submitted to Chemcut for testing. Perhaps in the near future etching equipment will be able to effortlessly transport even thinner material.
There are plenty of areas where we will likely see the photochemical machining industry flourish. A breakthrough on any of these 5 could be a big game-changer in technology because overcoming each one opens up new opportunities. At Chemcut we are always exploring new ways to improve the wet processing side of these areas. If you interested in what ways we are working to innovate wet processing, please feel free to contact us.
