DIY PCB Making for MSOP-12 SMD

[brenesrob]

Hey there,

First of all I'd like to thank everyone that has been helping me out with my projects here on the EEVblog forum.

Second, I designed a circuit and a PCB layout that uses a chip in an MSOP-12 package that includes a GND pad underneath of it. Due to the lack of manufacturers in my area I wanted to make my own PCB using the photoresist method, however, I am worried that I won't be able to get the traces small enough using this method for the MSOP package.

Therefore, I was wondering, has anyone had success making their own PCBs with such small traces? Is the photoresist method the best way for this? If not, then do you solely recommend a fab house for these types of prototypes?

Thanks in advance,
Roberto

[flolic]

Therefore, I was wondering, has anyone had success making their own PCBs with such small traces? Is the photoresist method the best way for this?

No problem at all using photoresist method 

[Psi]

I've never used the photoresist method but I have made fine pitch TQFP pads using the toner transfer method.

I'm not sure if the same thing will apply to you but the key i found was to oversize all tiny pads because they always over etched. This is because the etchant will eat sideways on a track as well as downwards. If the track is thick you dont notice as the percentage lost is tiny. But for small tracks this can become quite significant.

 eg a row of 4 correct pads might be like this

 ####      ####      ####      ####       
 ####      ####      ####      ####     
 ####      ####      ####      ####     
 ####      ####      ####      ####     

but it would end up like this after etching

    ##          ##           ##           ##
    ##          ##           ##           ##
    ##          ##           ##           ##
    ##          ##           ##           ##

So i just made them like this to start with

#####    #####    #####    #####
#####    #####    #####    #####
#####    #####    #####    #####
#####    #####    #####    #####


So the etching solution would return them to the correct width.

A proper etch tank which circulates the solution may eliminate this issue.
I just had a container of FeCl that i sat the PCB in and move it around on some wire.

[DarkPrince]

Yeah that isn't a problem. I'd mention though, work on a method to... calibrate yourself. Get a feel for how fast the developer works... how fast the acid etches. I had a test pattern where I exposed it for various increments of time, and etched it on the other axis for various amounts of time, to optimize the quality (also had various track widths to test stability of small traces). Good way to know what times to use for different processes.

I had taken a break for nearly 8 months since my last etch before two weeks ago... had to get the feel for it back! Timing was off, nearly had bad traces.

On the other hand... a turn-around time of only a hour/couple hours is wonderful.