Sunday, February 22, 2015

Meeting #4 - Recap

To celebrate a year of EAST Knowledge, Pat Nystrom returned for meeting #4 where he showed off two things:

  1. Recent work on his pick and place machine
  2. A DIY solder mask application

Pat is an engaging, knowledgeable speaker and he gave a tremendous talk. As usual, we’ll do our best to capture the meeting in these humble notes, but we won’t pretend to do the speaker justice. You really have to see these presentations in person.

Pick and Place Machine

When Pat last talked at EAST Knowledge he showed us his nearly completed pick and place machine. Pat’s goal is to produce a low cost pick and place machine for hobbyists and prototype assembly. He wants to combine what people do best with what machines do best. His pick and place machine will allow the human operator to pick up parts, while letting the machine perform final placement.

However, before finishing his machine, Pat was contacted to perform some other work that had extremely tight deadlines and required PCB assembly of multiple boards. The deadlines were so tight that he would not have been able to have the PCBs assembled by a manufacturing firm, so Pat turned to his mostly finished pick and place machine to assemble the boards himself. However, he found that while his current pick and place machine had buttery smooth motion when manually operated (as intended), it did not have the fine control he desired for part placement while being operated manually.

Manual Pick and Place

So Pat put together a new pick and place frame. For the two axes, this has rigid arms with small rollers that can be manipulated with the fingers for fine adjustment. Each axis has just enough stiction to keep from moving while the other axis is being adjusted. Additionally, Pat outfitted the parts head (taken from the previous machine) with a digital camera that he could use to see where the part was while placing it.

The machine isn’t perfect. For instance, the camera doesn’t have a perfect view of the part needle, so getting used to where the needle would place the part required a small learning curve. Despite the limitations, the machine allowed Pat to stuff 16 boards with small scale parts in about 4 hours without the fatigue and mistakes he would’ve experienced had he been using magnifiers and tweezers. Additionally, he successfully completed the prototypes. It’s hard to argue with success.

For the future, Pat would like to add a second camera to the head to provide a better view, and a laser dot that will provide an easy way to see where the part will be placed.

Lessons Learned

Beyond the technical issues, Pat felt he learned some valuable lessons while working on the manual pick and place. Being forced to work quickly required him to come up with ideas that he could try out quickly. This rapid pace allowed him to discover bad ideas earlier and discard them. Whereas before he was trying to get to product completion quickly, he is now thinking more along the lines of iterating his way to product refinement. Additionally, the manual pick and place is useful as it is right now even without all the automation. Focusing on having a useful product at each stage of development also allows for rapidly trying ideas.

It appears that the pick and place machine itself feeds into Pat’s entire process. It allows him to rapidly try ideas on not just the pick and place machine but also on the other things he works on.

DIY Solder Mask Application

After showing us his work on the pick and place machine, Pat gave a demonstration of a method he has developed for applying solder masks to his prototype circuit boards. Pat mills his own circuit boards, but the method will apply to any circuit boards you may make or have made. While you don’t need solder masks just for a prototype board, having a solder mask:

  • Improves the reliability of the board
  • Increases the lifetime of the board
  • Makes it easier to rework the boards

In short, it is often better to have a solder mask, so being able to apply a solder mask to boards you make yourself is a boon.

How it Works

Pat found a source of solder mask material that comes as a sheet. One side of the sheet is adhesive. This material is light sensitive, so Pat keeps it rolled up in a tube.

Required materials and tools:
  1. Solder mask material
  2. Solder mask stencil (it’s black everywhere you don’t want solder mask, i.e., over the component pads)
  3. Exposure frame
  4. Laminator (Pat used a Harbor Freight laminator)
  5. UV Light source (Pat used a lamp that is normally used to cure finger nail polish)
  6. Masking Tape
  7. Exacto blade
  8. Scissors
  9. Latex gloves (mostly for cleanliness)
  10. Canned air
  1. Warm up the laminator.
  2. Wash PCB and dry with canned air.
  3. Cut a piece out of the sheet of solder mask material to be bigger than your PCB. Pat used scissors to get a rough cut.
  4. Using masking tape, attach to the dull side of the solder mask sheet, and pull off the protective covering. This exposes the adhesive side.
  5. Apply the adhesive side to the PCB.
  6. Use the exacto blade to trim off the excess material.
  7. Run the PCB through the laminator. This will cause the solder mask material to adhere to the PCB surface.
  8. Tape the stencil to the bottom of the exposure plate. Make sure the ink side of the stencil is away from the plate (which will be towards the PCB).
  9. Close the exposure plate down over the PCB and align the PCB to the stencil.
  10. Once the stencil and PCB are aligned. Clamp the exposure plate down so that the PCB won’t move.
  11. Place the PCB into the UV light source for about 2 minutes. Let cure for another 5 minutes (optional).
  12. Remove the PCB from the exposure frame, and lift the top protective sheet from the solder mask.
  13. Use sodium carbonate and a brush to remove uncured solder mask material. Anywhere the UV light was blocked by the stencil should come right off.
  14. Rinse the board again.
  15. Enjoy your freshly solder masked PCB!

Pat was talking to the group as he demonstrated his method, but it looks like it only takes a few minutes of work to apply the solder mask.

Exposure Frame:


The UV source being applied to circuit board in the exposure frame:

The circuit board with solder mask applied. The green areas are where the solder mask stuck, and the copper areas are just the bare circuit board:

This was another excellent demonstration of Pat’s methods for quickly bringing his circuit ideas to life.