A presensitized circuit board is a special board with a photosensitive surface coating. It enables you to create a customized design by shifting/burning the image with a UV light. In other words, a presensitized circuit board resembles a standard copper-clad board. The only difference between them is how you transfer the design into the boards.
What re the differences of Presensitized PCB and normal PCB?
As mentioned above, the primary difference between a presensitized PCB and a traditional PCB is how you transfer the design into the boards. Basically, this is how you should transfer images in traditional PCBs:
·Toner transfer method
·Inkjet masking method
·By dry film photopolymer method.
On the other hand, you should expose your board to UV light to transfer images in presensitized PCBs. Generally, you add a photosensitive covering during the preparation process. A “peel-off” layer shields the covering from accidental light exposure. Remember to take away the “peel-off” layer before exposing your photosensitive coating to light.
How to Make a Presensitized PCB？
The first thing to remember is that circuit board printing demands a lot of effort, endurance, and testing! Therefore, bear in mind that you might experience some challenges the first time you design a photosensitive board, leading to errors. For this reason, you should prepare several experimental PCBs if it is your first time.
Besides, it is good to be in touch with a reputable PCB manufacturer to remain confident with the components you are using. This will further ensure your supply chain does not weaken, fade, or become problematic during the manufacturing process.
There is a common expression in the computer world that says, “Garbage In, Garbage Out.” The principle applies well with circuit board design. It simply means that your project will only worsen if you begin your project with the wrong artwork.
While there are numerous media you can use to print your circuit board artwork positively, you will get excellent results by printing your artworks on a quality tracing paper. Remember to scrutinize your tracing paper before utilizing it. Light up one part of the paper with a shiny source of light, and examine it by viewing through the other side. The paper should be free from dark spots and stains. Dark spots cover the artwork portions, forming short circulating pathways around crowded sections of the board artwork.
You should use laser-made positive artwork in your PCB printing exercise as they form delicate, crisps, and compact black prints. Inkjet inks seam to stain with tracing paper, resulting in prints with draining and blurry edges. Consequently, this limits the feasible spacing between circuit board pads and traces. Occasionally, bleeding can short circuit narrowly positioned patterns.
It is essential to realize that a presensitized board surface is shielded with a dense grey layer against unintended exposure and impurities. If the layer is still intact, the board can assume irregular treatment during cutting with a slight damage risk. Always remember to keep it intact until you are set for the exposure process.
Chop a board with two contrasting sides, measuring more than 5mm long. You will use the extended part later to attach your PCB standoff clip during the design and etching process. Burrs and uneven edges may limit your artwork from lying ideally uniform. Luckily, you can do away with them using a hand file.
First, clean your exposure box surface with a cloth containing a mild detergent. Then, rinse it with a clean, dry cloth. Remember to keep the surface free from stains and dusty particles to have the most satisfactory image transfer.
You can now set your board for exposure. Note that from this point onward, you should carry out everything under passive light conditions. This is because bright light might accidentally expose your board, essentially hindering your project.
Use the Easily Accessible Artwork
Take out the protective PCB layer. Remember to grasp your board along the edges to avoid touching the exposed parts. Additionally, do not put down the board until you finish the next step.
Thirdly, gently slide your board in between the upper and lower artwork. Place it accordingly to position and align the artwork at the center of the edges.
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