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On water break test

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1 parent 470e286 commit 816da2199503071bfa0eb2e5d23bf1598ba31759 @whitequark committed Feb 24, 2014
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@@ -292,6 +292,8 @@ Quality: nearly perfect.
Interlude: water break test
---------------------------
+**Update:** see [On water break test](/notes/2014-02-24/on-water-break-test/).
+
I've noticed that the very first try, despite horribly selected conditions, yielded one
of the best imprints. I've also noticed that each time I clean the PCB from exposed
(and unexposed) resist, there remains a visible ghost picture of the traces from previous
@@ -0,0 +1,37 @@
+---
+layout: post
+title: "On water break test"
+date: 2014-02-24 10:07:49 +0400
+comments: true
+categories:
+ - pcb
+---
+
+I have used the water break test (checking whether copper surface is clean of contaminants
+based on the fact that really clean copper is hydrophobic) [in the past][photoresist], however
+I misunderstood how the test results must look.
+
+[photoresist]: /notes/2014-02-16/optimizing-for-best-photoresist-adhesion/#interlude-water-break-test
+
+<!-- more -->
+
+The PCB on left was immersed in NaOH 5%wt for 10 minutes, as in the note above.
+The PCB on right was left in same solution for about 11 hours.
+
+{% fancybox /images/pcb-cleaning/2014-02-24/water-break-test.jpeg 700 %}
+
+Only the right PCB truly passes the test. The amorphous blob on the picture is a really
+thin film of water uniformly (unlike a drop) spread over that area.
+
+I have thought that if water film spreads and remains on PCB for a few seconds, it means
+the surface is clean. Evidently, this is not the case. In fact, it is very easy to remove
+water from PCB on left by tilting it, whereas for the PCB on right it is only possible to
+wipe it or wait until it dries on its own.
+
+There are no immediately visible differences between resist attachment to two boards, but
+it seems that with properly cleaned board, resist sticks to it better in extreme circumstances:
+when it's placed over drilled holes or after it was contained in aggressive etching solution
+for >40 min:
+
+{% fancybox /images/pcb-cleaning/2014-02-24/good-attachment.jpeg 700 %}
+
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