Flashing and etching are both the addition of a conductive material to a printed circuit board, or PCB. That’s where the similarities end.
We’ll start with flashing. First let’s look at the largest misconception that often comes up; ‘but it has gold plate’. Flashing is not plating. Plating can be chemically removed from the PCB, remelted into the original base, and then used to make jewellery or bullion coins. As we’ll get to later plating is extremely valuable, in bulk, and explains quickly the high value in scrap such as cell phone boards and military equipment, ram cards (sticks), etc. So, what is flashing. Flashing is paint. In fact, flashing is the same paint you can buy at lowes, Home Depot, or Ace to paint your walls. The material is called metallic paint. It’s made from an oil based paint by adding metallic particles (dust) to the oil base, a conductive precious metal (pm), and an organic or chemical pigment to keep the paint the same colour as the PM or change it to a specific colour requested. The dust is usual either tin or aluminium; both readily bond with most PM and Rare earths (RE). There’s less than one penny weight of pm per gallon of paint. So little, in practice, that the few chemical companies that recycle, or salvage, metallic paint do so for the dust and oil base, and cast off any pm along with carbon waste to be sold as iron additive (slag) in making steel. How is flashing done. Flashing is applied to pcb in a process know as lithography. This is the same technique used to print out colours on plastic film used on soda bottles. The paint is added to a special plate of metal, usually a tube, and rolled across a statically neutral pcb. It is then cured in a statically positive low temperature oven, or in modern boards by uv light, for a few seconds to a few minute where the paint dries and sets.
What it’s used for Flashing has three uses. The first is generally useless. For decoration. Companies such as Biostar and eVGA print cool designs for no reason other than to make cool designs. Asus and ASRoc(k) use it for names and logos. Custom designers such as eXc print the whole board in a custom design for the client.
The second, and most common use, is dampening. There are two aspects to this. The more common use is a tracing. Either the complete edge of the board, or geometric shapes around specific objects in a process I don’t fully understand this reduces the electromagnetic (em) and radio frequency (rf) discharge from boards or components. It basically creates a 2d faraday cage. And is a must for selling in the US and Japan where radio and em leakage is heavily governed and restricted.
The final use for flashing is as a ground out. Such use will always find the flashing connected to one of two things An etching A through hole for mounting screws. The later is more commonly seen. Most modern motherboards have flashing around screw holes. This utilises the same idea as the em etc leakage. Any signal buildup, such as static, can be properly directed to a (hopefully) properly grounded spacer or case. Protecting the user from any external discharge; and more importantly protecting expensive components from burnout. Such design is also occasionally found on/in embedded systems, and historically in mainframes and mini computers. Here, the flashing is always in contact with an etching. This is used with fuses and breakable circuits where when the fuse, or switch, is tripped the electrical charge is redirected to the flashing via the etching; there being directed to a physical grounding. Such a design is used when wires (to a power supply) are undesirable, unfeasible, or impossible.
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