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The PCB Fabrication Techniques

As a PCB designer, it may be tempting to depart the small print of the manufacturing process as much as the fabrication house. Nonetheless a little understanding of the manufacturing process upfront can help stop headaches further down the line.

In this post we’ll cover the totally different types of PCB fabrication methods, and what you as a designer have to know about designing for manufacturing.

Imaging

Imaging is the place the magic happens: your digital PCB design gets switchred onto the physical board. Today photoimaging is the way to go, the general concept being to use a fabric that hardens upon exposure to ultraviolet light called photoresist. Here’s how it typically works.

A dry film is produced by inkjet printing the negative image of the PCB circuit design.

The copper surface of the board or panel is coated with liquid photoresist.

The film is aligned with the copper surface of the board and subjected to UV light.

Only the exposed areas of the photoresist harden into place, protecting the copper traces underneath.

The remaining liquid photoresist is removed and the board is ready for and so onhing to remove the excess copper leaving the traces behind.

Alternatively, in case you’re working with a fabrication house they could have more costly equipment which permits you to skip the dry film and directly apply the sample to copper coated with photoresist through a UV laser.

And so onhing

And so onhing is the process of removing excess metal from a PCB with an industrial solvent. It’s typically performed after the imaging step to remove the excess metal away from the traces protected with hardened photoresist. It’s also used to determine a uniform surface. Common and so onhing chemical substances embody ferric chloride, cupric chloride, alkaline ammonia, and ammonium persulfate.

Lamination

Your typical PCB consists of a number of layers of copper interspersed with non-conductive substrate (normally epoxy impregnated fiberglass) comparable to FR4. Lamination entails using heat and pressure to melt together the completely different layers of a PCB.

Single-layer laminate: One substrate layer with copper laminated on one side.

Two-sided laminate: One substrate layer laminated with copper on both sides, typically called a core in multi-layer laminates.

Multi-layer laminate: Typically start with one core, and stack alternating layers of prepreg (substrate without the copper) and copper in both directions to the required number of layers.

As the PCB designer, it’s important to be aware of the things that may go flawed throughout the lamination process with the intention to be prepared to switch your design accordingly. For a first time fab, the house will typically do a couple of prototype runs to hone in on an excellent lamination heat profile. Relying on the outcomes, you might must scale your images to account for any shifting that may occur as a result of the materials and thicknesses used in your build.

Machining

Machining can happen multiple times throughout the PCB manufacturing process relying in your design. Let’s take a look at where machining is utilized in PCB manufacturing:

Through-holes and vias: It’s doable to avoid wasting time and money by stacking a number of boards collectively, securing them in place with stakes, and drilling your by holes. Normally, you’ll want to drill non-plated holes and vias towards the end of the manufacturing process, after you’ve applied photoresist, soldermask, and silkscreen.

Panelization: Panelization saves time by allowing a number of boards to be fabricated and tested directly as a panelized array. A drill can be utilized to route channels, machine vscores or create breakaways (mouse bites), to allow simple removal of the boards towards the top of the manufacturing process.

PCB thickness, material selection and types of drilling (mechanical or laser) are vital considerations for manufacturability. To drill via fiberglass similar to FR4, you need a good tungsten carbide drill bit. In case your design has smaller holes it means you’d have to make use of thinner drill bits. These thin drill bits are likely to snap easily, so the more small holes it’s essential to drill right into a board, the more a fabrication house will are inclined to cost you.

It’s also possible to use a laser instead of a drill bit for drilling smaller vias. The laser is less appropriate to use for bigger diameters. So, it’s important to use the appropriate machining technique on your design.

Plating

Want to apply a metal end (e.g. gold) to your via-holes and vias? You’ll must plate it onto the desired surface using one in every of these frequent methods:

Electrolytic Plating: Good for high-volume finishing projects. The boards are bathed in a concentrated solution of the plating metal. A current is applied to plate the exposed metal surfaces on the board (your via-holes and vias) by way of electrolysis.

Electroless Plating: Instead of utilizing a present to plate metals in a solution onto your board, you may also use catalysts and self-reducing agents to use a finish (no exterior current required). The main advantage is a more even coating that is not susceptible to anomalies that may be caused by current flowing across an irregular shape.

Plasma/Dry Plating: For fine-line circuit plating, an inert gas plasma is used to remove metal particles from a charged target to be redeposited onto the target surface. The process should be operated under a vacuum.

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