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When I made my first attempt at a board, I realized after I used too concentrated of a developer solution and most of the traces came off. This time I'm going paranoid and I put in about 1 cup of water to maybe 3 tablespoons of developer (but I didn't use a spoon to measure). My question is, whats the maximum amount of time one should leave a board sitting in developer? I want to use this time as a factor to gauge how much developer I should pour in.

I'm using the standard positive developer from MG chemicals. Also, I use blacklight as my exposure source.

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    \$\begingroup\$ I think I now know the answer to your previous question. The answer is process control: you need to actually measure your chemicals so you will get consistent results. \$\endgroup\$
    – The Photon
    Jul 20, 2016 at 3:31

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Nobody can answer your question but you. Only YOU have your combination of board, resist, developer concentration, temperature, etc. etc. You must establish some consistent "process control" where you know exactly how much developer concentrate you are mixing with some measured amount of water.

Typically, you can make a strip of board marked off in several divisions. Then you can dip the whole board for 1 minute, pull out the first section and leave the rest in the solution for 1 more minute. Then pull out to the next section for 1 more minute. Etc, etc, etc.

Then your board will have the first section processed for 1 minute, the second section for 2 minutes, the third section for 3 minutes, etc. Then you can look at the finished "test strip" board and see exactly how your (MEASURED) solution performs with your resist at various times. Then you can select the time right in the middle of "too little" and "too much".

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According to my experience, preparing the developer solution is easier part. Just follow the instructions: correct mixture, concentration and temperature (unfortunately, I can't comment on positive developers, for negatives Na metasilicate or simply "liquid glass" just works OK, hard to overdevelop). If your developer is MG 418, it shall be 1 part for 10 parts of water?

The exposure is tricky part, since it depends on custom setup: photoresist type, age, mask quality, light type, radiation, distance to the PCB etc (it could be 3 minutes as well as 20 minutes), maybe finding most similar setup case will help estimate the timing. Usually everyone finds own configuration by experimenting as Richard Crowley suggested.

In your case, underexposure might be a good starting guess. Try several test samples with increased exposures. Also board must be clean from grease, some sanding is a good practice. If it is film photoresist, usually it must be passed (wrapped with paper) through hot laminator to get better adhesion. If spray type, I heard the thickness shall be considered. Some photoresists requires 5-10 minutes "resting" time to complete the polymerization after exposure (in dark of course). Failing in any of these requirements could potentially lead to broken traces.

UPD:

Since yours is positive photoresist, it is more likely OVEREXPOSURE, not underexposure that leading to dissolved traces.

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