Exposing and Developing a Pre-Sensitized PCB (Printed Circuit Board):

 

Note:  There must be a UNLV staff member present while making the PCB!

 

Don't layout your board such that the traces go right to the edge of the PCB.  Some times the light sensitive coating doesn't fully cover the board.  You can always trim your board to a smaller size after etching.

 

Sizes currently in the lab (tell Mark when supplies are running low):

100mm x 150mm; 3.91'' x 5.91''. Single-Sided, 1oz Copper Foil on Fiberglass Substrate.

100mm x 150mm; 3.91'' x 5.91''. Single-Sided, 1oz Copper Foil on Fiberglass Substrate.

150mm x 300mm; 5.91'' x 11.81''. Double-Sided, 1oz. Copper Foil on Fiberglass Substrate.

 

I have some of these in Physics if needed:

114mm x 165mm; 4.6'' x 6.6''. Single-Sided, 1oz. Copper Foil on Fiberglass Substrate

114mm x 165mm; 4.6'' x 6.6''. Double-Sided, 1oz. Copper Foil on Fiberglass Substrate

 

1) The material safety data sheet for the developer (Sodium Metasilicate) will be posted on the corrosive cabinet.  Review it before continuing.

 

2) Put on rubber gloves and eye protection.

 

3) The positive developer used is a white powder contained in small (50gram) plastic bags.  Avoid skin and eye contact with developer and don't inhale the dust.  Mix one developer packet with one liter (or one quart) of water in a plastic tray large enough to hold the board you are working with.  Once mixed the developer has a shelf life of about one day.  You can develop about 10 single-sided boards or 5 double-sided boards (4X6") before the developer is used up.

 

4) Take the pre-sensitized PCB out of package and trim to the size needed.  If remaining pieces are of a useful size put them back in foil package and tape shut.

 

5) Turn on red safe light and turn out room lights.

 

6) Peal off white protective coating on board

 

7) Lay the transparency (ideally, printed side down) on the board and place in the light box.

 

8) Place a piece of glass over the transparency to keep the transparency against the board

 

9) Close the light box and expose for about five minutes (the room lights may be on while exposing).  Warning: Do not operate the light box with the lid open.  The bulbs produce large amounts of UV light.

 

10) With the room lights out and the light box turned off, open the light box.  Set the glass and the transparency to the side.

 

11) Place the board in the developer and lightly agitate the developer.  Be careful not to scratch the surface of the board with the tongs.  After about four minutes (or when the image is clear) remove the board from the developer and rinse off any remaining developer with water.

 

12) Turn on the lights and inspect the board.  If the board appears fogged turn off the lights and develop longer.  Use a permanent marker to fix bad traces.  Use an exacto knife to scratch away material in the wrong place.

 

13) If the PCB is OK and no one else will be using the developer that day pour it down the sink and rinse the developing tray and sink with water.

 

14) Let a UNLV staff member know if there is a shortage of material

Etching a Copper Clad PCB (Printed Circuit Board):

 

Note:  There must be a UNLV staff member present while making the PCB!

 

1) The material safety data sheet for the etchant (Ferric Chloride) will be posted on the corrosive cabinet.  Review it before continuing.

 

2) Put on rubber gloves and eye protection.

 

3) Carefully pour the etchant (brown bottle of Ferric Chloride) into the etching tank to a level sufficient to cover your board.  Plug in the heater and air pump.  If you get any Ferric Chloride on you wash the exposed area thoroughly and notify the UNLV staff member.  If you spill any on the sink clean the area quickly (also run the water for a while to rinse and dilute any portion not picked up).

 

Note: The etchant can be used many times but will eventually need to be replaced.  When it takes longer than one hour to etch a board it's time to mix new etchant (Note: if the etchant is cold it may take longer than one hour).  Using a funnel, carefully pour the etchant back into the brown bottle and notify the UNLV staff member.  They will properly dispose of the etchant.  Before mixing new etchant make sure there is another storage bottle available to hold the etchant.

 

Mixing etchant:  Fill the etching tank about 2/3 full with water.  Slowly pour one or two packages of Ferric Chloride powder into the water.  Note: the water will heat up and bubble so go slow.  Once the package or packages are empty add water to the etching tank to bring the water to the full line.  Turn on the heater and air pump and continue as normal.

 

4) Use tape to cover copper areas around the edge of the board.  This will make the etchant last longer by not having to dissolve excess copper that you will later trim from the board.

 

5) Place two plastic holders on the PCB and place the board in the etchant.  The top of the board (or at least the top of your circuit) should be submerged.

 

6) Check the progress of the etching board periodically by grabbing the plastic holders and pulling it partially out of the etchant.  Rinse off any etchant that spills.  Note:  If the etchant is fresh and hot it can etch a board in 10 minutes.

 

7) When the board is done remove and rinse it under running water to remove excess etchant.

 

8) Turn of the heater but let the air pump run for five more minutes.  This helps cool the heating element.

 

9) Using a funnel, carefully pour the etchant back into the storage bottle.  Clean the outside of the bottle and sink as needed.

 

10) Place the etchant back in the corrosive storage cabinet.

 

11) Let a UNLV staff member know if there is a shortage of material

Drilling Holes in the PCB (Printed Circuit Board):

 

Note:  There must be a UNLV staff member present while drilling!

 

Recommended trace widths (mils - thousandths of an inch):

Traces smaller than 10mils may be dissolved in the etching process.

I recommend trace widths of 25-30 mils unless it's a high-density layout.

Use wider traces for high current connections (i.e. power in & out of the board).

 

Recommended pad sizes (mils - thousandths of an inch):

                              O.D.               I.D.                Comment

DIP                       70               25               no trace between pins

DIP                       55               25               15mil trace between pins

TO-220  70               35

TO-92                   55               21

1/8W Resistor               70               25

1/4W Resistor               70               28

1/2W Resistor               70               28

1W Resistor               70               35

2W Resistor               70               35

DO-35 Diode               70               21

DO-41 Diode               70               35

 

Available Drill bits:

.429mm

.0135"

#80

 

1.3208mm

.052"

#55

.3683mm

.0145"

#79

 

1.397mm

.055"

#54

.4064mm

.016"

#78

 

1.5113mm

.0595"

#53

.4572mm

.018"

#77

 

1.6129mm

.0635"

#52

.508mm

.02"

#76

 

1.7018mm

.067"

#51

.5334mm

.021"

#75

 

1.778mm

.070"

#50

.5715mm

.0225"

#74

 

1.8542mm

.073"

#49

.6096mm

.024"

#73

 

1.9304mm

.076"

#48

.635mm

.025"

#72

 

1.9939mm

.0785"

#47

.6604mm

.026"

#71

 

2.0574mm

.081"

#46

.7112mm

.028"

#70

 

2.0828mm

.082"

#45

.74168mm

.0292"

#69

 

2.1844mm

.086"

#44

.7874mm

.031"

#68

 

2.2606mm

.089"

#43

.8128mm

.032"

#67

 

2.3749mm

.0935"

#42

.8382mm

.033"

#66

 

2.4384mm

.096"

#41

.889mm

.035"

#65

 

2.4892mm

.098"

#40

.9144mm

.036"

#64

 

2.5273mm

.0995"

#39

.9398mm

.037"

#63

 

2.5781mm

.1015"

#38

.9652mm

.038"

#62

 

2.6416mm

.104"

#37

.9906mm

.039"

#61

 

2.7051mm

.1065"

#36

1.016mm

.040"

#60

 

2.794mm

.110"

#35

1.0414m

.041"

#59

 

2.8194mm

.111"

#34

1.0668m

.042"

#58

 

2.8702mm

.113"

#33

1.0922m

.043"

#57

 

2.9464mm

.116"

#32

1.1811mm

.0465"

#56

 

3.048mm

.120"

#31

1.3208mm

.052"

#55

 

1.3208mm

.052"

#55