As example, when i made the prototypes for try the MAX8715, i ruined all the pcb for a stupid error (my guilty, too much hydrogen peroxide in the HCl), and i'm actually waiting for other thin coppered plates, so i'm stopped til they arrives.
When making a PCB using insolation method there are some points in the process where epic fail is typical:
1º The printing in the transparency is not opaque enough.
Solution:
If using a laser printer, use maximum toner setting and use toner darkener spray.
If using an inkjet printer, print it with the highest photo quality available, and IMMEDIATELY after the printing is finished pour some talcum powder in the ink side and extend it properly. Then remove the leftovers with a soft tissue. That will both dry the ink and make it more opaque. That's the method I use and I can achieve almost professional resolutions.
2º There are air gaps between the transparency and the boad, so the contact is not perfect and some shadows appear. This may ruin thin tracks.
Solution:
The cheapest and most effective method available for holding the transparency against the boad with pressure is just sandwiching the board and the transparency between twho pieces of glass, and holding it with paper with this kind of clips:
http://www.exchange3d.com/cubecart/images/uploads/aff586/aa.jpg
Don't forget to put a small piece of board material where the clip clips the two pieces of glass, to avoid cracking it. This method also allows easy double-layer PCB's. You align both transparencies and glue them together making an envelope that will sandwich the double layer PCB
3º The PCB gets overdeveloped: lower the exposure time
4º When etching, the PCB gets more etched in the center than in the borders or the etching is irregular or excessive:
Use a slower etchant such as ferric chloride, and use it in small amounts. Instead of pouring half a litre of etchant in the tray and reuse it for a long period, just pour enough etchant to cover the PCB or even less, and keep rubbing the PCB with latex gloves during the etching process. Be careful not to breath the vapors. After the PCB is done just discard the etchant. It's way better to always start with fresh etchant than to reuse a big amount of etchant until it stops working. Same applies with the developer.
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