As a PCB designer, it will be tempting to leave the details of the manufacturing process up to the fabrication house. Nonetheless a little understanding of the manufacturing process upfront can assist prevent headaches additional down the line.
In this submit we’ll cover the totally different types of PCB fabrication methods, and what you as a designer must know about designing for manufacturing.
Imaging
Imaging is the place the magic happens: your digital PCB design gets switchred onto the physical board. As of late photoimaging is the way to go, the final concept being to make use of a cloth that hardens upon exposure to ultraviolet light called photoresist. Here’s how it generally 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 uncovered areas of the photoresist harden into place, protecting the copper traces underneath.
The remaining liquid photoresist is removed and the board is ready for etching to remove the surplus copper leaving the traces behind.
Alternatively, in case you’re working with a fabrication house they might have more expensive equipment which lets you skip the dry film and directly apply the pattern to copper coated with photoresist by way of a UV laser.
And many othershing
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 surplus metal away from the traces protected with hardened photoresist. It is also used to establish a uniform surface. Common etching chemical compounds embrace 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 (often epoxy impregnated fiberglass) reminiscent of FR4. Lamination includes using heat and pressure to melt collectively 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, often 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 essential to be aware of the things that may go flawed during the lamination process with the intention to be prepared to modify your design accordingly. For a primary time fab, the house will typically do a couple of prototype runs to hone in on an ideal lamination heat profile. Relying on the outcomes, you could need to scale your images to account for any shifting that will occur as a result of the supplies and thicknesses used in your build.
Machining
Machining can occur multiple times throughout the PCB manufacturing process relying on your design. Let’s take a look at the place machining is utilized in PCB manufacturing:
Through-holes and vias: It’s attainable to avoid wasting time and money by stacking a number of boards collectively, securing them in place with stakes, and drilling your by means of holes. Usually, you’ll wish to drill non-plated holes and vias towards the end of the manufacturing process, after you’ve utilized photoresist, soldermask, and silkscreen.
Panelization: Panelization saves time by allowing multiple boards to be fabricated and tested at once as a panelized array. A drill can be utilized to route channels, machine vscores or create breakaways (mouse bites), to allow straightforward removal of the boards towards the top of the manufacturing process.
PCB thickness, materials selection and types of drilling (mechanical or laser) are important considerations for manufacturability. To drill through fiberglass comparable to FR4, you want a good tungsten carbide drill bit. If your design has smaller holes it means you’d have to make use of thinner drill bits. These thin drill bits tend to snap easily, so the more small holes you need to drill right into a board, the more a fabrication house will are likely to charge 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 larger diameters. So, it’s vital to use the appropriate machining method to your design.
Plating
Want to use a metal end (e.g. gold) to your via-holes and vias? You’ll have to plate it onto the desired surface utilizing certainly one of these common techniques:
Electrolytic Plating: Good for high-quantity 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 by means of-holes and vias) through electrolysis.
Electroless Plating: Instead of utilizing a present to plate metals in a solution onto your board, you may as well use catalysts and self-reducing agents to apply a finish (no external present required). The main advantage is a more even coating that’s not inclined to anomalies which may be caused by current flowing throughout 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 must be operated under a vacuum.
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