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Old 16th October 2004, 11:40 AM   #1
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Question --- Leach Amp PCB Coatings - HELP ---

Hy everybody!

I want to build my own PCB for the Leach Amp, but I have a few questions.

The PCB is made with photo UV method and i finished the PCB including drilling but my true problem start here ....

After drilling what are the steps to protect the copper traces ?

Some people say PLASTIK 70 other say FLUX SK 10 but I heard
that FLUX must be removed at the end ... ? I'm very confused

Some datasheets for these two sprays .. PLS

I go crazy because I don't know how to continue ...
Please tell me a solution step by step
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Old 16th October 2004, 04:00 PM   #2
lykkedk is offline lykkedk  Denmark
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Just use e.g SK10 lotlack, or something like this, it's for preventing the cubber from 'oxyating' - remember to clean the drillholes (use a bigger drill, with you'r fingers), and clean the PCB, before using this. And let it dry 24H. I did this 2year's ago, and my PCB are still fine.
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Old 16th October 2004, 04:08 PM   #3
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OK, but when do I coat the PCB with flux ?

... right away after cleaning the UV lacquer (PCB drilled, no component on PCB) or after all components are soldered ?
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Old 16th October 2004, 04:11 PM   #4
lykkedk is offline lykkedk  Denmark
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when your'e done drilling the holes / before mounting the component's
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Old 16th October 2004, 04:17 PM   #5
lykkedk is offline lykkedk  Denmark
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And when your'e done with soldering, you can clean the hole pcb, with a glasslike brush (ask a dealer) - and some electronick cleaner, and give it flux again, for keeping the pcb nice and clean - the idea with the flux, is to make better soldering, and protect the pcb. You have to clean the hole pcb, when your'e done soldering, because it will look like sh.. then... when you read the leach-amp instruction's he is also mentioning it here!

good luck
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Old 16th October 2004, 04:22 PM   #6
Eva is offline Eva  Spain
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As a crude solution, if you used positive PCB with the UV sensitive layer built-in, you can keep that layer as a cheap and simple copper protection instead of cleaning it after etching

The strength and solderability of this layer may vary a lot between manufacturers, but for the material I use it works fine, it protects copper for years and it doesn't affect soldering at all since hot solder removes it very easily

Also, if you clean this layer too soon, days or even hours before soldering, copper may get dirty and oxidized enough to make soldering a pain

The board on the left was etched more then two years ago. The board on the right was etched a week ago
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Old 16th October 2004, 04:35 PM   #7
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I also intend to do a double side board for a vu-meter and to spray it with PLASTICK 70 RED varnish over both sides before soldering, because if I spray after soldering, copper traces under IC socket remain vulnerable at moisture, dust, etc

Also I want a more profi PCB ...

How it looks a pcb coated with PLASTICK 70 RED varnish ?
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Old 16th October 2004, 05:38 PM   #8
sss is offline sss  Israel
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i'm also using a positive UV pcb , i have never coated it with any type of protection , i just put solder on all traces

btw

i have a problem making very dark transparencies with my printer
how do u guys do that
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Old 16th October 2004, 09:06 PM   #9
Eva is offline Eva  Spain
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I get acceptable results by printing the masks in paper and then doing two photocopies on acetate transparencies. Then I use both photocopies supperposed, taking care to make them match and to place the toner sides facing down [closer to the PCB]

I use a heavy piece of glass to force the sheets to make good contact with the PCB

Two layers of toner are much more efficient than one at stopping UV light, so the UV sensitive layer doesn't get sensitized and weakened where it should'nt and thus etching time and concentrations are not so critical

It would be better to print the masks directly on acetate with a laser printer but I don't have access to one

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Old 16th October 2004, 10:10 PM   #10
dangus is offline dangus  Canada
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I vote for leaving the photoresist on the board. It's easy to solder through (unless you coated it yourself and used too much). I wouldn't worry about the traces under the ICs, although you could always spray a generous amount of conformal coating and let it run under the chips. I've done the "coat everything with solder" thing in the past, but it doesn't look as smooth as factory, and it requires an uncomfortable amount of heat to tin big areas, enough that I see signs of delamination.

I've used the electroless tin coating. It can look nice if the copper is very smooth to begin with, and if the tin coating is buffed afterwards (scrap piece of blue jeans worked for me). However, the tin oxidizes too, so it still needs protection.

The tool I use for cleaning the pads was called a "Rust Eraser" pen, found in the body repair section of an auto parts store. (that must be the same "glasslike brush" that lykkedk uses)

As for printing artwork: laser printers (and photocopiers) aren't that good; they just fundamentally seem to have a tough time doing wide black areas. This is one place where inkjets are superior. I've had good results using inkjet transparency film, stacking two copies to improve the density. Since the transparency film isn't cheap, it makes sense to print several copies on a single sheet, and if possible use the sheet more than once (print near the bottom).

I just discovered Irfanview image viewing software. http://www.irfanview.com/ I was having a hard time getting some artwork to print to scale, but Irfanview let me specify the dpi and print it exactly. Irfanview can also join images to make panoramas; I used that feature to print multiple images side by side (copy the image to several differently-named files first).
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