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Ecthing notes

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Thomas Quinot 3 days ago
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_source/_posts/2024-11-24-pcb-etching.md
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@ -19,8 +19,7 @@ Minimum with / Minimum trace separation: 0.3 mm (12 mil)
All tests with 8 W/m UV LED strip (4x25cm) @ 100% All tests with 8 W/m UV LED strip (4x25cm) @ 100%
Test 1 ## Test 1
------
Double layer tracing paper Double layer tracing paper
10 zones from 30 s to 5 min in 30 s increments 10 zones from 30 s to 5 min in 30 s increments
@ -30,8 +29,7 @@ Double layer tracing paper
Best result: 2 min Best result: 2 min
Test 2 ## Test 2
------
Single or double layer tracing paper Single or double layer tracing paper
5 zones: from 1 min 30 to 2 min 30 in 15 s increments 5 zones: from 1 min 30 to 2 min 30 in 15 s increments
@ -40,8 +38,7 @@ Single or double layer tracing paper
* Develop with solution for at least 3 min * Develop with solution for at least 3 min
* Good results at 2 min exposure * Good results at 2 min exposure
Test 3 ## Test 3
------
4 layers transparency film 4 layers transparency film
10 zones: from 1 min 35 to 3 min 05 in 10 s increments 10 zones: from 1 min 35 to 3 min 05 in 10 s increments
@ -52,7 +49,9 @@ Best results in zones 4-5: 2 min 05 / 2 min 15
* Develop again a few minutes * Develop again a few minutes
* Wipe with isopropyl alcool to remove last traces of gunk * Wipe with isopropyl alcool to remove last traces of gunk
# Actually etching the board, try 1 # Actually etching the board
## Try 1
I printed several stencils but they would not line up: it appears that my printer (HP MFP 1217nfw) expands in the Y direction significantly and in a non-uniform way. I printed several stencils but they would not line up: it appears that my printer (HP MFP 1217nfw) expands in the Y direction significantly and in a non-uniform way.
To get good registration of the stencil, I had to print on 3 separate sheets of transparency film, keeping the design centered on the sheet (not at the top of the page, which would have allowed me to print two designs on the same sheet). To get good registration of the stencil, I had to print on 3 separate sheets of transparency film, keeping the design centered on the sheet (not at the top of the page, which would have allowed me to print two designs on the same sheet).
@ -72,3 +71,20 @@ Lessons learned:
* do a hardening exposure (also serving as a double check that there's no leftover resist) * do a hardening exposure (also serving as a double check that there's no leftover resist)
* use fresh etching solution (2 parts H2O2 / 1 part HCl) * use fresh etching solution (2 parts H2O2 / 1 part HCl)
## Try 2
* Exposed 1 min 30 with 3 layers of stacked transparency film. => **this was plenty for hard traces protection**
* Rinse+++ the unexposed film => gently swipe with tooth brush to really eliminate all gunk
* Etched with a softer solution
* 100 mL water / 50 mL HCl / 25 mL H2O2 (12%)
* Ecthing is much slower, allowing better control over the process, less Cl2 vapours
* Removed resist with NaOH (a few grams in hot water)
* Fixed broken tracks by soldering pieces of resistor legs
Lessons learned:
* 3 stacked transparencies seems right
* Laminate film super carefully, avoid bubbles at all cost. **Each bubble will be a broken trace down the line**
* No need for water
* Heat+pressure from iron
* 1 min 30 is plenty, 1 min might work and reduce overexposure of protected areas
* Try gentle swipe with scotch brite to remove gunk during development?

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