Before starting any experimentation, even if it’s just prototyping on breadboards you need to think about…

• Seeing yourself as a giant resistor. Sounds a bit silly right? It’s true though, the human body does have some resistance to electric current. To stay as safe as you can when working with electronics you need to think about the stuff then can increase or decrease that resistance. If you’ve got sweaty hands, lots of metal jewellery on and are standing in a puddle you’re not really in a good position to be using electricity! Normally the human body has a resistance of anywhere between 50,000 to 1,000,000 ohms (the range is so big as it depends on body chemistry, path that resistance is measured over etc.) if you’re in the situation above you can have lowered that resistance to to as low as 100 ohms!
• Electricity can really hurt! when electricity comes into contact with a person’s body it can cause intense muscle contractions and generate a high heat at the contact point. If the current is strong enough this can cause heart attacks and 3rd degree burns. It may be fun to tinker with circuitry but never forget the effects that the power running through them can have. You should never run circuits from mains electricity until you are really experienced, AC current (mains: 240V) ignores everything in the point above and treats your body as a giant capacitor! The metal you touch is one plate and the tissue under underneath your skin is the other with your skin itself acting as the dielectric. Voltage shocks this high can burn right through your skin. So, no mains experiments. 
• Static is bad, and not just for your ICs, some components can store a charge. Capacitors for example, are designed to hold a static charge, if you don’t discharge a capacitor properly it can shock you. With little capacitors this can be annoying but larger ones used in power supplies can store a lethal charge. To discharge a capacitor properly place a bulb across it’s terminals using insulated crocodile clips,you’ll be able to see when it has discharged as the bulb will go out. If you don’t have a bulb handy put a 10K resistor across the terminals and wait at least 30 seconds. You can check the discharge using a multimeter. 

Here’s a good electricity safety check you should do before starting any work:

Make sure you have

1.  a dry working surface.
2. a dry floor.
3. dry hands or gloves to wear.
4. removed any rings, watches or other jewellery.
5. a first aid kit, phone and preferably a friend close at hand

The soldering was quite easy, some of my GCSE knowledge came drifting back up from where it was buried in my brain plus a couple of the guy’s here have worked as electrical engineers (thanks Steve!)

Tips:

• Make sure that you heat up the lead and the track before touching the solder to the iron, this helps the solder flow to both. (you can see this in the photo to the right)
• ‘Wet’ the end of the iron first by touching the solder lightly to the tip of the iron so just a little adheres to the end.

Right now I’ve finished soldering my components (note that I did not have a terminal block so my battery leads are just soldered straight to the board) I need to see if it will work. First thing I need to do is to perform a visual inspection, this is crucial as a bad/crossed connection can cause your battery to blow up! Here’s the procedure I followed to make sure there were no unexpected bangs:

VISUAL INSPECTION

Looking for:

Soldering errors

Board errors

Component errors

BACK

1)      Ensure all pins are soldered

2)      Are there any solder bridges? (too much solder flowing over to another contact)

3)      Are there any dry joints? (where the solder is not joined to the track and the lead)

4)      Looking for continuity of copper tracks and bridges (checking the mask, was it exposed properly?, was it too long in the solution?)

5)      Are the holes drilled in the right place? (not breaking the tracks)

6)      Are the leads trimmed properly? (don’t bend leads at right angles when soldering!)

7)      Has the board been produced with the artwork the right way round?!?

FRONT

1)      Check the values and placement of components

2)      General condition of components (no cracks, corrosion etc.)

3)      Are the polarised components in the right way round? (anodes and cathodes)

4)      Is anything loose? (links to solder inspection on the back)

Right now I can be as sure as I can be that nothing untoward will happen when I connect up my circuit to the battery pack, here goes…

POWERED INSPECTION

1)      Is anything heating up? (Be careful!)

2)      Does it smell of burning?

Well I still have all my fingers and both eyebrows are intact, now all I need to do is to plug it into a computer and try to programme it.

There are a few things to keep in mind when using the laser cutter:

• Never use without turning on the extraction! The laser melts through the material being cut and can release harmful fumes. It also causes damage to the machine by fogging up the mirrors and making the laser less efficient.
• Never look directly at the laser beam as it can cause eye damage.
• Always make sure that the laser is set to the correct power and speed, if it is set to too high an intensity it can set light to the material on the laser bed.
• If cutting acrylic sheet remember to remove the protective covering from both sides of the material as it causes risk of fire, harmful fumes and will ruin the surface of the piece you want to cut. 

I pulled this safety information from the Boxford website (http://www.boxford.co.uk/boxford/docs/products/t220.htm#safety accessed on 14/01/2011):

Safety equipment features

• Full perimeter guarding with interlocking switches on access doors arranged in the positive (safety) mode for spindle stop and feed hold.
• Overload cut-out on spindle drive.
• Positive end stops on all axes.
• Mandatory graphics run required for new programs before matching cycle can be commenced and step by step execution of graphics in advance of cut in machining cycle.
• Integrated electrical panel with no volt supply protection.
• Feed rate over-ride.
• Feed hold.
• Latching emergency stop button.
• power on indicator lamp.
• Low voltage control circuitry.

I have found that whilst working with this machine that as long as you double check your measurements (stuck-out, billet dimensions etc) and make sure that the work piece is properly secured then you shouldn’t have any problems in manufacture.

You should always wear protective clothing (even if it’s just to stop nasty yellow splotches from the ferric chloride on your clothes) and goggles. Always read the health and safety sheets before mixing or using any of the chemicals involved.

The Rota-Spray has a safety cut off in the lid, if it is reaised during etching the motor will cut out.

By having the wash tank connected to the spray tank it reduces the risk of dripping the etchant on yourself, the floor or any surfaces.

Uses/Processes

To produce, by etching away unwanted copper, an electronic circuit board designed to meet a specific requirement. 

The prepared board is immersed in ferric chloride (iron (III) chloride) solution or sodium peroxodisulfate (persulfate) solution to etch away the copper.  The board is sometimes cleaned with a solvent before or after soldering, formerly mainly 1,1, 1 – trichloroethane, now propan-2-ol (isopropanol) or other alcohols (e.g. ethanol).

Assessment

Sodium peroxodisulfate (OES of 2 mg/m3 – 15 min ref period) and ferric chloride are harmful if swallowed and steps should be taken to minimise the risk of ingestion.   Mist produced makes it less suitable for use in a bubble-etch tank.  When used with a small manual developing tray, little mist will be produced.

If the two etchants are mixed, toxic chlorine gas is produced.

Propan-2-ol has an OES of 500 ppm (15 min ref period).  Ethanol OES is 3000 ppm (15 min ref period).  If applied by a brush (not a spray) these concentrations will not be approached in a school electronics area.

Iron salts have an OES of 2 mg/m3 (15 min ref period).  If the solution is prepared with gentle agitation and used in a tank with a lid, the mist produced will be minimised.

Solid etchants and the etching solution can be irritant to the skin or respiratory system.

Controls

Eye protection and protective gloves must be worn when preparing solutions and emptying tanks.  If the processes are carried out in bubble tanks, the lids must be fitted to contain any mist.

Ferric chloride and sodium peroxodisulfate should not be available together in one workplace to eliminate the possibility of mixing.  See over for changing etchants.

Users with cuts or sensitive skin must wear disposable plastic gloves.  The wet boards must always be handled with plastic tongs.

Ignition sources should be removed from the area when using highly flammable solvents and natural ventilation is required to keep the minimise the level of vapour.

If a single bubble-etch tank is used, it is recommended that a base board is used to improve stability.  The tank can be held in an aluminum U-channel with sides at least 100 mm high and screwed to the board.

Storage

Both substances should be stored in a secure, well-ventilated area.  Ferric chloride should not be stored in the vicinity of metals.

Disposal

Solid waste of both etchants should be placed in appropriate containers and passed to an authorised waste disposal contractor.  Used ferric chloride solution should be neutralised with sodium carbonate and flushed away.  Emptying the tank requires  care and a siphon pump is recommended.

If changing from ferric chloride to sodium peroxodisulfate (or vice versa), the tank must be washed out thoroughly before filling with the new etchant.

Solutions of sodium peroxodisulfate should not be stored in sealed containers but may be re-used until they are a deep copper-sulfate blue when they can be well diluted and flushed away.

Immediate Remedial Measures

If swallowed: Wash out mouth thoroughly with water and give plenty of water to drink.  Obtain medical attention.

If mist is inhaled: Remove from exposure.  Keep warm and at rest.  In severe cases, obtain medical attention.

If in the eyes: Irrigate immediately with water for at least ten minutes, holding eyelids apart.  Obtain medical attention.

If spilt in workshop:  Dilute with copious quantities of water and swill away.