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Re: [Homebrew_PCBs] Re: photo layer coming off

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  • Harvey White
    ... As a complete guess on the exposure, look for a good exposure to be 3 to 4 minutes. This is based on my own experiences, different photoresist, more UV
    Message 1 of 24 , May 13, 2013
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      On Mon, 13 May 2013 18:36:03 -0000, you wrote:

      >cheers for the advice I will try another test strip but go over longer time.
      >The uv box is a converted scanner with four UV 9W tubes from a nail curing unit
      >The boards are positive photo from Maplins
      >it is clear acetate lazer printer. I print 2 images to double up the thickness

      As a complete guess on the exposure, look for a good exposure to be 3
      to 4 minutes. This is based on my own experiences, different
      photoresist, more UV light (perhaps).

      I do think that 15 seconds is way too small.

      Positive photoresist is a polymer (long chain molecules). It is
      damaged (read unlinked, read broken apart) by UV light. This happens
      from the top down to the board surface. The mask prevents that from
      happening.

      Under UV light, the top down starts to change into a form that can be
      dissolved. Note that the stripper is just a more concentrated
      solution, so we're dealing with degrees, not absolutes.

      Underexpose, and with too strong a developer, you tend to strip the
      board. That very thin layer of photoresist may not work to keep the
      etchant away.

      You may want to check the strength of your developer. IIRC, it took
      very little time (15 to 30 seconds) to "develop" photoresist.

      Harvey


      >Dave
      >
      >--- In Homebrew_PCBs@yahoogroups.com, "smilingcat90254" <smilingcat@...> wrote:
      >>
      >> One thing not mentioned so far is to cure the image after exposure-development.
      >>
      >> After the image is developed on the board, some recommend to cure the remaining resist by exposing the image to harden the image. Some resist may not be compatible with this step so check first.
      >>
      >> Another issue is resist adhesion. Lots of discussion on this too. I always wear rubber glove to keep the board free of oil from my hand and to keep chemicals off my hand. Some even have recommended to mildly pre-etch the blank then apply the resist. And so on...
      >>
      >> If you want to be accurate with exposure, you might want to use Stouffer's 21 step exposure guide. do a google search if you want one.
      >>
      >
    • Mitch Davis
      ... My 2c: When making boards at home I print onto drafting paper. 8mil is no problem:
      Message 2 of 24 , May 13, 2013
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        On Tue, May 14, 2013 at 2:36 AM, dave_donlan <dhd01@...> wrote:
        > cheers for the advice I will try another test strip but go over longer time.
        >
        > it is clear acetate lazer printer. I print 2 images to double up the thickness

        My 2c: When making boards at home I print onto drafting paper. 8mil
        is no problem:

        http://capnstech.blogspot.com/2011/05/playpause-making-pcbs-at-home.html

        Drafting paper is transparent to UV, and I worry less when it goes
        through the printer.

        (And now my plug: I supply pro-quality PCBs, double sided everything,
        10 boards for USD19 inc worldwide delivery.
        http://tinyurl.com/hvpcbfaq)

        Mitch.
      • Jeff Heiss
        Do you mean $19 per board when 10 boards are ordered ($190 total)? What is the cost for one or two boards? Jeff _____ From: Homebrew_PCBs@yahoogroups.com
        Message 3 of 24 , May 13, 2013
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          Do you mean $19 per board when 10 boards are ordered ($190 total)? What is
          the cost for one or two boards?



          Jeff

          _____

          From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
          On Behalf Of Mitch Davis
          Sent: Monday, May 13, 2013 10:56 PM
          To: Homebrew_PCBs@yahoogroups.com
          Subject: Re: [Homebrew_PCBs] Re: photo layer coming off





          On Tue, May 14, 2013 at 2:36 AM, dave_donlan <dhd01@...
          <mailto:dhd01%40live.co.uk> > wrote:
          > cheers for the advice I will try another test strip but go over longer
          time.
          >
          > it is clear acetate lazer printer. I print 2 images to double up the
          thickness

          My 2c: When making boards at home I print onto drafting paper. 8mil
          is no problem:

          http://capnstech.blogspot.com/2011/05/playpause-making-pcbs-at-home.html

          Drafting paper is transparent to UV, and I worry less when it goes
          through the printer.

          (And now my plug: I supply pro-quality PCBs, double sided everything,
          10 boards for USD19 inc worldwide delivery.
          http://tinyurl.com/hvpcbfaq)

          Mitch.





          [Non-text portions of this message have been removed]
        • Mitch Davis
          Hello Jeff, hello homebrewing PCB folks. First, something on-topic: When I was getting started with home etching, I also made a test strip. I used my CAD
          Message 4 of 24 , May 13, 2013
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            Hello Jeff, hello homebrewing PCB folks.

            First, something on-topic: When I was getting started with home
            etching, I also made a test strip. I used my CAD program (KiCad) to
            place 10 SOIC-14 footprints at 1-inch intervals, and wired each chip
            to its neighbours with traces of various thicknesses. After printing
            (see the blog entry from my last group email), I made marks at 1-inch
            intervals on the back of the blank board. Then I got two pieces of
            card, and slipped the blank between them with only the last inch
            hanging out. Off to my UV light, and I started a timer. Every thirty
            seconds I pulled out another inch, so that after about five minutes,
            I'd exposed all of the strip. I then developed and etched it. What I
            found was that for my UV light setup, and the blank I was using, 2½-3
            minutes was fine. I was able to get reliable 8mil traces through
            drafting paper with only one run through the printer. (I should point
            out that my making of boards at home is entirely unconnected to the
            professional PCBs I supply to customers)

            On Tue, May 14, 2013 at 11:39 AM, Jeff Heiss <jeff.heiss@...> wrote:
            >
            > Do you mean $19 per board when 10 boards are ordered ($190 total)?

            Haha, oh goodness no! I wouldn't do any business! That's USD19 total
            for 10 boards.

            As an example, this customer paid me the Australian equivalent of
            USD19 for these boards:

            http://nanibox.com/2013/03/kurobox-prototype/

            He also paid USD3 for registered shipping, but that's it. (He and I
            are both Australian so it was easier for us this way).

            According to my records, for his order, I checked and processed his
            order same day, board manufacture took 3 days, and shipping was 7
            days.

            There are some other important details: That's the up-to-5x5cm price,
            and for Paypal it's +5%. For more info, read my guide:

            http://tinyurl.com/hvpcbfaq

            > What is the cost for one or two boards?

            I have a 10-for-5 offer for boards that are up to 5x5cm (USD19), and
            10-for-5 on up to 10x10cm (USD36, but smaller sizes are cheaper.
            Also, thinner is cheaper). If you're really only after one or two, 'm
            very happy to make 5 and throw 3 or 4 away before shipping them to
            you. Or you can give them to budding engineers or use them for SMT
            soldering practice.

            Oh, and here's another happy customer:

            http://electronics.ozonejunkie.com/2012/11/pcb-manufacture/

            His boards were also USD19, but he also paid me USD25 for DHL.

            If you're greedy, you can visit these too:

            http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=4722
            http://dangerousprototypes.com/2012/12/06/workshop-video-interview-with-mitch-from-hackvana/

            Talking to my customers is the highlight of my day. I have a 24-hour
            live chatroom where several dozen of my customers hang out and talk
            about electronics, give feedback to each other on their PCB designs,
            and generally have a good time. You're all welcome to join (see my
            guide).

            Like most of you I'm an engineer and a tinkerer. I love making stuff,
            and I get a buzz out of helping others to make stuff.

            Lest I wear out my welcome here, if you'd like to know more, please
            send me a private email, or come chat with me and other customers in
            the chat room.

            Regards,

            Mitch.
          • Paul
            Hi Mitch More power to you, it s a really great idea to have someone on the ground as an interface between Europe/USA and the Chinese PCB makers although I
            Message 5 of 24 , May 13, 2013
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              Hi Mitch

              More power to you, it's a really great idea to have someone on the
              ground as an "interface" between Europe/USA and the Chinese PCB makers
              although I do have a great Chinese friend in HK who is into specialist
              electronics manufacturing and who helps me out.

              A couple of questions

              How about a sideline in supplying some PCB materials for us homebrew
              hackers? Pre-sensitised board is expensive here and solder resist
              laminate film is expensive and very difficult to find in small quantities.

              What kind of costs for a solder paste mask? (I saw somewhere you can
              supply them)

              Do you miss the Fosters?

              Ooops that's three questions.....

              Regards

              Paul

              On 14/05/2013 05:44, Mitch Davis wrote:
              >
              > Hello Jeff, hello homebrewing PCB folks.
              >
              >
              >
              > On Tue, May 14, 2013 at 11:39 AM, Jeff Heiss <jeff.heiss@...
              > <mailto:jeff.heiss%40comcast.net>> wrote:
              > >
              > > Do you mean $19 per board when 10 boards are ordered ($190 total)?
              >
              > Haha, oh goodness no! I wouldn't do any business! That's USD19 total
              > for 10 boards.
              >



              [Non-text portions of this message have been removed]
            • Mitch Davis
              ... That s what I do. I speak Chinese so you don t have to. I check boards thoroughly and give a report on each one. This saves you a lot of time and money.
              Message 6 of 24 , May 13, 2013
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                On Tue, May 14, 2013 at 2:11 PM, Paul <paul@...> wrote:
                >
                > More power to you, it's a really great idea to have someone on the
                > ground as an "interface" between Europe/USA and the Chinese PCB makers
                > although

                That's what I do. I speak Chinese so you don't have to. I check
                boards thoroughly and give a report on each one. This saves you a lot
                of time and money. And I'm there to make sure the fabs do a great job
                every time.

                >I do have a great Chinese friend in HK who is into specialist
                > electronics manufacturing and who helps me out.

                I'd be interested in talking to him, as I don't have good contacts for assembly.

                > How about a sideline in supplying some PCB materials for us homebrew
                > hackers? Pre-sensitised board is expensive here and solder resist
                > laminate film is expensive and very difficult to find in small quantities.

                I'd really love to. One issue is freight. Fibreglass is extremely
                heavy. Freight for a few boards can often end up more than for the
                boards. For another issue, see below.

                > What kind of costs for a solder paste mask? (I saw somewhere you can
                > supply them)

                I was selling laser-cut stainless frameless solderpaste stencils of up
                to A4 in size for USD25. I have stopped doing that for the moment
                though, as I really really have to concentrate on getting web ordering
                of PCBs going. (And 90% of that is the back-end processing, not the
                customer-facing stuff).

                If you'd like to make your own solderpaste stencils, it's not hard:

                http://lowpowerlab.com/blog/2013/02/11/diy-smd-metal-stencils-the-definitive-tutorial/

                I think everyone should try that. (Felix is another customer of mine :-) )

                > Do you miss the Fosters?

                LOL, Fosters is megaswill, I never drink it. I brew my own beer :-)
                That's what this group is for eh, making your own?

                Mitch.
              • Mitch Davis
                ... I should clarify that I check the design. Here s a recent report for a customer: - No board outline file. Please see attached. The purple lines should
                Message 7 of 24 , May 13, 2013
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                  On Tue, May 14, 2013 at 2:26 PM, Mitch Davis <mjd@...> wrote:
                  >
                  > I check boards thoroughly and give a report on each one.

                  I should clarify that I check the design. Here's a recent report for a
                  customer:

                  - No board outline file. Please see attached. The purple lines should
                  be a rectangle enclosing the whole board. You can have right angle or arc
                  corners. In particular, please pay close attention to the shape of the
                  board in the area of the four RJ45 connectors (or whatever they are).

                  - Be aware of PCB manufacture limitations if your final board outline
                  has sharp angled concave corners near the RJ45s. It's not possible to
                  faithfully reproduce sharp angled concave corners. The mill bit is 0.8mm,
                  and therefore the smallest radius of curvature of the arc you'll get on
                  concave corners is 0.4mm. Please let me know that this is ok.

                  - The fab will "pull back" copper very slightly so there's no copper
                  right at the very edge of the board. There will be a very thin copperless
                  margin right around the board. If you don't want the fab to do pullback
                  (for example, if your design had SMA connectors) then please tell me and
                  I'll tell the fab.

                  - Many packages use .dri for drill files, but Eagle wants to put drill
                  holes into .txt files. That's ok, but the files to include in your .zip
                  are the .txt files. (Also, with our .cam file, we can't find a way to stop
                  Eagle from generating useless .gpi files, sigh).

                  - On the top you have silkscreen across the pads. What will happen is
                  that the soldermask will be used to mask the silkscreen - silkcreen will be
                  omitted where it crosses pads. This is not a fatal problem, but if you're
                  expecting to get back boards where the silk looks just as you designed it,
                  this can be a bit of a shock. The easiest solution to this is to redefine
                  your footprints so no silk crosses the pads, but you'll still need to
                  carefully review every part of your board if you want a total remedy.

                  - The "XYZ" text is covering up "ABC".

                  - No silkscreen on the bottom layer (that's ok, but please tell me it's
                  intentional).

                  My chat channel is also a very good place to get a review.

                  Mitch.


                  [Non-text portions of this message have been removed]
                • Paul
                  ... But they keep telling us on the TV ads that it is amber nectar! You imply they are telling porkie pies? :-) Real ale myself... proper Brit stuff. I do brew
                  Message 8 of 24 , May 14, 2013
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                    On 14/05/2013 07:26, Mitch Davis wrote:
                    >
                    >
                    >
                    > > Do you miss the Fosters?
                    >
                    > LOL, Fosters is megaswill, I never drink it. I brew my own beer :-)
                    > That's what this group is for eh, making your own?
                    >
                    > Mitch.
                    >
                    > _
                    But they keep telling us on the TV ads that it is amber nectar! You
                    imply they are telling porkie pies? :-) Real ale myself... proper Brit
                    stuff. I do brew although none on the go at the moment.

                    Paul


                    [Non-text portions of this message have been removed]
                  • Mitch Davis
                    ... That it was an ad should be enough of a giveaway, that it was also on the TV means it s incredible. Desperate attempt to stay on topic: How long does
                    Message 9 of 24 , May 14, 2013
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                      On Tue, May 14, 2013 at 3:45 PM, Paul <paul@...> wrote:
                      >
                      > But they keep telling us on the TV ads that it is amber nectar!

                      That it was an ad should be enough of a giveaway, that it was also on
                      the TV means it's incredible.

                      Desperate attempt to stay on topic: How long does presensitised board
                      last when the bag is sealed? How about once it's been opened but then
                      sealed up? (Not talking about what the manufacturer recommends, which
                      is probably going to be "after using your 2x2cm square, throw the rest
                      of the board away" but what folks have found for themselves...)

                      Cheers,

                      Mitch.
                    • lists
                      In article , ... Thank God for that. -- Stuart Winsor Midlands RISC OS and Raspberry pi
                      Message 10 of 24 , May 14, 2013
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                        In article
                        <CA+KzSgJHRQsZ3gojr0ij=1UkLBWx-MdtbHRscDmzLUKbLxarHQ@...>,
                        Mitch Davis <mjd@...> wrote:
                        > > Do you miss the Fosters?

                        > LOL, Fosters is megaswill, I never drink it. I brew my own beer :-)

                        Thank God for that.

                        --
                        Stuart Winsor

                        Midlands RISC OS and Raspberry pi show, 13th July 2013

                        http://www.mug.riscos.org/show13/MUGshow.html
                      • lists
                        In article , ... Maplin - Arrgh Bought some board from them once, they had to order it because they had none in stock at the
                        Message 11 of 24 , May 14, 2013
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                          In article <51914A6B.9000102@...>,
                          Paul <paul@...> wrote:
                          > Maplin board!

                          Maplin - Arrgh

                          Bought some board from them once, they had to order it because they had
                          none in stock at the local shop. That was usual. I would go in with a list
                          and if I was lucky they might have two of the items I wanted - must have
                          cost them a fortune in postage because they would send direct from head
                          office post free.

                          When it turned up it seemed to be covered in scratches, which I judged
                          would have gone right through the protective film and the photo-resist. I
                          complained and they sent me a replacement piece that looked worse than the
                          first - looked like somebody had been kicking and scuffing it around on
                          the floor. I was in a hurry and desperate so I had to use it - broken
                          tracks everywhere where the scratches had removed the resist.

                          One would have thought that because I had complained they would have
                          checked the replacement over before sending it out.

                          --
                          Stuart Winsor

                          Midlands RISC OS and Raspberry pi show, 13th July 2013

                          http://www.mug.riscos.org/show13/MUGshow.html
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