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PostPosted: Mon Sep 03, 2018 6:12 pm 

Joined: Tue Feb 03, 2015 6:57 pm
Posts: 4546
Location: Low DOS
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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PostPosted: Mon Sep 03, 2018 6:13 pm 

Joined: Tue Feb 03, 2015 6:57 pm
Posts: 4546
Location: Low DOS
Etching
Etching, and it’s opposite, embossing, are a form of material plating and filling.
We’ll start with embossing since it’s easy to follow.
Embossing has one use in technology: edge connectors (fingers). It’s actually not an accurate description but you’ll see what the name in a moment.
With embossing an entire pcb is plated with a thicker than flashing layer of a conductive material alloy: 18k gold, or, silveride, an alloy of silver with aluminium and/or tin, or, silver.
Tin or Copper are also found on low end boards.
Once the plating process is completed the material is removed from all of the board except where the plating is wanted. Termed embossing because the plating is above the surface of the pcb, rather than below it.
Technically etching since the connector plating is etched off the majority of the board.

So what is etching. Etching, less commonly and originally wire etching, is the the removal of the top layer of the pcb in thin lines. It is used as an alternative to wires. It both offers better air flow and more room, and increases reliability br reducing the number of breakable solder points on a board.
It is created by gouging thin lines, then filling in the lines with a conductive material; silver and gold being the most common.
Depending on the thickness etching can be very inexpensive or quite valuable. Today it’s done by robots controlled by computers and individual board productions are consistent by product. See end note

End note:
Let’s go back to embossing for a moment. It does show up in one other scenario. In the earlier days wire etching really was hand painted on top of the pcb. And today the DIY movement of pi boards, raspberry, apple, strawberry, the tongue-in-cheek cherry. Metallic paint is mixed by the tech and painted with thin tiny brushes or pipe cleaner. These have a materials value of unknown quantity. It depends on the ‘artist’ who did it.
Mind you on old equipment painted wire etches may be filled with lead on very inexpensive or very high production boards. Lead is extremely toxic in many many ways.

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