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  • Author Author: fmilburn
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Microscopes and Solder Masks

fmilburn

Now that the TI-RSLK robot RoadTest is finished I have turned my attention back to a problem spotted in the last round of PCBs ordered for the AIS alarm project.  But first, I have a new toy.

image

I have been looking for the right used Nikon microscope in budget but finally could not stand it any longer and bought this Chinese model after my friend bought one.  I am amazed at how much better this is than peering through a magnifying glass or loupe.  At low magnification stereoscopic details pops and there is good depth of field.  I bought a version that takes a C-mount camera but don't have a camera yet.  Good value for the money I think but this was a "want" rather than "need" purchase.

 

I went back and put some of my old PCB designs under the microscope and discovered several had a problem I reported in a previous blog - that is, the solder mask did not extend between the pins of smaller SMD packages.  This of course makes solder bridging and the resultant need for rework more likely.

 

I have had the problem occur for two reasons:

  1. The PCB manufactures had a minimum guaranteed spacing specification between the pad and the solder mask.  Check the specification especially with low cost prototyping services.
  2. I use KiCad and the default pad mask clearance is pretty high - so high that there is no mask between some SMD pins.  For KiCad the fix is to go into Dimensions -> Pad Mask Clearance while in pcbnew and change the default to the desired value.  OSHPark has a discussion on the topic and recommends 2 mil (0.05 mm) clearance for 2 layer boards.

 

The MSP430FR2xxx protoboard I put together a while back had the second problem and I did not realize it until I looked under the microscope.  They were made by OSH Park and it is hard to see the problem with the naked eye on that purple background.  Pesky default values....  I have reordered the board with the fix since they are inexpensive and I have another project in mind for that particular microcontroller.

  • in reply to Fred27

    Mine came with a 2x as well as the 0.5x.  I tried the 2x for the first time last night and as you say it will be great for the kids and may come in handy for some electronic stuff.  The distance to the stage really shrinks and it is no longer possible to easily work under it.  The depth of field is also greatly diminished of course.  Fun stuff....

  • in reply to rachaelp

    Hi Rachel,

     

    Thanks for all the great information.  Mine is an Amscope but my friend has one that appears identical under a different brand name.  As you say, the reviews I have seen are all good and I have been impressed so far.

     

    Thanks for your thoughts and insights on a camera.  As cheap as cameras are these days, it is somewhat surprising that the ones for microscopes are so expensive although I realize it must be a relatively small niche market.  I have a long time interest in still photography but have never been too interested in video so some study is in order.  Whatever I come up with I will post here on Element14. 

     

    RE:  solder mask - I am not an experienced PCB designer although I have used CAD software quite a bit.  Most (really all) of the errors I encounter can be traced back to me :-)

     

    Regards,

    Frank

  • in reply to fmilburn

    As far as I remember it was impossible to get the focus even close to being right. It got thrown in a box and I've not tried anything else as it wasn't really a priority. It was a cheap one from eBay so other adapters may be better.

     

     

    For anyone getting one of these I can recommend also getting a 2x barlow lens. When I got mine the two pack of barlow lenses was a good deal. The 0.5x is ideal for soldering and general electronic work, but the 2x is even better if the kids want to be grossed out by a spider, etc. You might as well get more use out of it!

  • in reply to Fred27

      wrote:

     

    Nice microscope. I've got the same one. I got mine with a camera included but it captures a much smaller area than you can see through the eyepiece. I intended to sort out something better but haven't managed to yet. Tried a DSLR C mount adapter without success.

    Hi David,

    Thanks for the comment.  I was planning to try a C mount adapter for my DSLR.   Can you describe more  the issues you had with it? 

  • Nice microscope. I've got the same one. I got mine with a camera included but it captures a much smaller area than you can see through the eyepiece. I intended to sort out something better but haven't managed to yet. Tried a DSLR C mount adapter without success.