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DIY PCB Etch Tank - FR4 Double-sided PCB Test


The last post on using the DIY PCB Etch tank was about performing a single-sided PCB test on (Sunday April 11th 2010) which was exactly 2 months ago. This date is quite significant as the PCB etchant, used in that test, should be quite close to the end of its shelf life. This was at the back of my mind as I etched another PCB although this time a double-sided one, using the same solution. 

Undeterred, by using what could be considered to be a slightly weaker etching solution, I decided to perform a double-sided test. This time the test was to be performed on a real design a DC Motor controller board. The result of etching the demo board can be seen in Figures 1 and 2. 


Figure 1: Top Side of the DC Motor Controller Circuit: The components have been test fitted and all seems well, even though the top and bottom layers have not registered as well as they could have done (see right hand side). The lack of perfect registration, of the top and bottom layers, has no bearing on the finish however as most of the components are soldered on the bottom side.


Figure 2: Bottom Side of the DC Motor Controller Circuit: There are no significant problems despite the less than ideal registration of the two layers.  Some "tidying-up" (1-2 hours of work) of the design should be performed around the IDC connector. This could have been avoided if a keep-out layer had been used, during the PCB design phase, to prevent the hatched ground plane from encroaching onto the IDC pin connections.  The result is very pleasing indeed especially when you consider that manufacturing a double-sided 100mm x 80mm PCB with soldermask and silkscreen, using a popular online PCB manufacturing company, would have taken 8 working days and cost 83.74 EUR! The details of etching the design are given below:



Figure 3: The aim of this particular exercise has been to etch the design of a DC motor controller on a 100mm by 80mm double-sided PCB. I used a hatched ground plane instead of a solid ground plane. A PCB  design with a hatched ground plane seemed easier to transfer to the copper clad board when using the "press-n-peel" blue method.


Figure 4:  The "press-n-peel" blue method has been used with a dry iron to transfer the bottom layer....


Figure 5: ... and the top layer. Transferring the top layer did not go as smoothly as I would have liked it to. It might be a good idea to rewash the second layer to remove any grease and other artefacts that may have occurred during the transfer of the first layer next time.


Figure 6: The PCB was inserted into the etching solution at a temperature of approximately 38.3o Celsius. Note that a second heater has been added to hasten the time taken to warm the etchant and possibly shorten the etching time or so I thought!


Figure 7: It took approximately 27 minutes to etch the board "completely" at an average temperature of around 40o Celsius.


Figure 8: The etched bottom layer: The etchant should be used roughly at a temperature of between 40o and 50o Celsius which would indicate that better results could be obtained if the etchant solution is raised to a slightly higher temperature. This could mean that the heaters would need to be physical modified to allow the heater's regulators to work at this higher temperature. 


Figure 9: The etched top layer. As expected. Good! Together the process has gone exceptionally well considering that I have not modified the heating elements, yet, or "strategically" placed the airline to maximise its use.


Figure 10: Temperature Profile: The temperature profile would suggest the second heater has shortened the time it takes for the etchant to heat up to 37o Celsius by about 30 minutes. However, the ambient temperature at this time of the year is higher by about 4o -5oCelsius compared to when the single-sided test was performed. The second heater however has not aided the etching process at all as it has taken about the same time, at the same temperature, as the single sided test.


Figure 11: The contents of the etch tank have been safely stored away ready for use next time!  


A homemade PCB etch tank like this one not only allows for the rapid prototyping of designs, it allows the hobbyist the luxury of experimenting with a large variety of designs secure in the knowledge that it will not cost an arm and a leg to manufacture each design iteration.

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