Friday, April 10, 2015

Dissolving copper in a chemical bath by immersing and agitating.

WARNING: The chemicals used in this process are dangerous!
Dihydrogen Monoxide is a colorless and odorless chemical compound, it is a polar solvent capable of solving hydrophilic substances. 
Iron(III) chloride is toxic, highly corrosive and acidic. The anhydrous material is a powerful dehydrating agent. Ingestion of ferric chloride can result in serious morbidity. 
These experiments were conducted in a well ventilated area while wearing all of the appropriate safety gear and having taken precautions against any spills or splashes.

Dissolving copper in a chemical bath by immersing and agitating.

The use of iron(III) chloride to dissolve away copper from a double sided 35 µm copper-clad fiberglass board.


The solution was prepared:

As the iron(III) chloride dissolves in dihydrogen monoxide at the rate of 92 g/100 mL at 20 C the acid was added to the solvent at the rate of 110 g/100 mL at 30 C.
An amount of 20 g of sodium chloride was added to further increase the chloride concentration.
The solution becomes a iron(III) chloride - chloride ion - dihydrogen monoxide system.
The container used was a clear plastic box with a detachable lid. The dimensions were as follows: 15 cm * 10 cm * 5 cm.
The amount of solution produced was 320 mL.

The subject was prepared:

The test subject was a 2 cm * 1 cm piece that was attached to a 6,5 cm long 1mm diameter wooden dowel by a narrow strip of a double sided adhesive tape.
A thick layer of oxide was cleaned by the process of abrasion with a 1000 grit Aluminium oxide/Silicon carbide sandpaper.
The copper surface was then cleaned of any oils by application of a thin coating of industrial grade distilled ethanol with a soft cotton material.

The experiment:

Immediately after the last visually distinguishable signs of solvent had vaporized, the subject was introduced into previously prepared solution.

While maintaining constant depth the subject was moved around in the solution and observed.

At 20 second mark a discoloration of the surface of copper was observed. The copper seemed to acquire a lightening pinkish hue and became dull.
At 65 second mark only approximately 10% of the copper remained.
At 90 second mark the reaction was considered complete and the subject was removed from the solution and placed on a stack of porous cellulose material to absorb the solution.

The subject was then immersed in a tank of dihydrogen monoxide and agitated for 4 seconds.

Subject was again placed between layers of a porous cellulose material.
Momentarily pressure was applied and then the subject extracted.

Subject was then carefully detached from the wooden dowel and analysed to detect any remains of metal.

As by optical analysis no traces of metal were found the experiment had succeeded.

Conclusion:
The use of iron(III) chloride to dissolve away copper is a viable method up to at least 35 µm * 2cm *1cm * 2 of copper.
The experiment can be further optimized by using a less pure solution as presented in another study "Effects on etching rates of copper in ferric chloride solutions" by Jian Cai ; Dept. of Mater. Sci. & Eng., Tsinghua Univ., Beijing, China ; Ma Jusheng ; Wang Gangqiang ; Xiangyun, T.


TL;DR!
I wanted to know how long it takes to etch a PCB.
So I stuck a piece of double sided FR-4 copper board in new salted FeCl3 solution and got less than 2 minutes when you clean the board properly and move it around.

Thursday, April 2, 2015

An SMD 4 digit 7 segment diy display

I was designing an electronic clock to see time easier at night. And while at it, I came up with a nice idea:

Having used a lot of perfboards(dot pcb) to prototype my projects, I thought of a way to make a 7 segment display out of smd leds. Making a segment out of 2 common grounded leds..
I stumbled upon it while trying to determine a nice size for my clock. I drew a mask on perfboard with a marker. Later I redrew it and cut it out:

I soldered on all of the 58 smd leds:




And then used a 0.25mm(30AWG) coated wire to make connections:




That gave me a nice bunch of leds:

All of the segments are connected in the usual matrix style. Every segment is a row and every digit is a column. 
The 12 pin header is configured: A, B, C, D, E, F, G, Dots, D1, D2, D3, D4

I forgot to connect the dots ground. It can be connected to whichever digit as another extra segment.