Printed Circuit Board processing back to projects
|For all projects involving the use of printed circuit boards (PCB's) use is made of a small chemical lab. In this lab photoresist is exposed, developed and copper is etched away. Below an impression of how this could look, but the process can also be done in the kitchen sink;)|
|The tools required for the process are an ultraviolet lamp, a development bath, an etching bath and (running) water for rinsing. For the Ultraviolot exposure unit the housing of a scanner device is used and some UV lights are installed. These are the fluorescent types, but nowadays the use of UV leds can be considered. LED's do perhapps suffer less from ageing and do not require a warm-up time for constant light production. Below a picture of the UV exposure unit with some printed circuit examples.|
|after exposure the PCB is developed in a solution of NaOH and the result of this will look something like the picture below.|
|Following the developed board is rinsed thoroughly in preferably running water. A soft sponge can be used to remove persistent photoresist remains. The next step is to etch away the (not by photoresist protected) copper from the epoxy carrier material. This is done in a bath filled with ammoniumpersulfate and water, heated to around 60 degrees Centigrade and exitated with bubbling air. There are other etching agents, but I think this is a very convenient way to etch copper.|
|After etching the board is rinsed thoroughly again to remove remaining etching liquid. The remaining photo resuist can be removed with acetone.|
The process in a table.
for inkjet:use quality transparency film, for HP use CG3460 (3M) or similar. printsettings: transparency film, best quality. remarks: photo quality gives sometimes more resolution, but color ink is used, which can be less UV blocking.
For laser printer transparency film is ok for low-res designs. Transparency film has the property that a lot of loose ink-particles are spread all over, reducing the resolution. An advantage of usiing the film is that UV is barely blocked and therefore the exposure is short.
Printing on normal paper delivers the best possible resolution for laser printers (as far as I'm concerned). Therefore, a better solution is to print the design simply on normal paper (60-80 gr/ sheet). The exposure time must then be increased by a factor 3-4. Better do the exposure a bit longer, the ink blocks the UV perfectly.
|3||turn on UV lamp for > 2 minutes||Warm the lamp before use to be sure of similar exposure doses|
|4||place sheet and photo sensitive PCB on the UV lamp||Apply pressure to ensure good contact|
|5||Exposure with UV||Time is depending on photoresist type and lamp strength|
|6||Development||use KOH or NaOH solution, 10 grammes / liter, develop-time is around one minute|
|7||rinse with water||Rinse with (preferably warm) running water and softly rub the surface with a soft sponge to remove all resist and developing solution remains|
|8||etching||Etch in FeCl3 or ammoniumpersulfate( (NH4)2S2O8) bath (approx 100g/l), temperature 50 to 80 degrees|
|9||cleaning||rinse with water|
|10||dry||dry with tissue-paper|
Some common used etchants and their properties
|Etchant||Price||Ease of use||Replenish ability|
|Hydrogenchloride with peroxide||+||-||+-|
Removal of photoresist after etching. This process does not require acetone.
|1||flood exposure with UV lamp||not time critical|
|2||developing in KOH or NaOH||Use standard or discarded developer|
|3||rinse with water|
|5||apply protective layer||for preventing the copper layer to oxidise|
|6||let dry thoroughly|