Display boards populated

Mark decided to work on the Flash display drivers this weekend to finish populating the cards.  He is now done, and has tested the boards and they all display.  I know I like pictures so here are some.

Here is the board taped with the Kapton stencil.  The stencil reduced the amount of time to populate the boards significantly.  The second picture shows all of the boards populated.  That would be 4 player boards, and the master display board.

Kapton Stencil for surface mount parts

Kapton Stencil for surface mount parts

All displays now populated

All displays now populated

One thing to watch for is solder bridging especially around the dual channel FETs for driving the segments.  Here is a picture of two solder bridges that needed to be fixed.


Shorted pins on dual N channel FET

Shorted pins on dual N channel FET

The short is the small bit of solder between the bottom three pins.  This is a highly magnified picture and a little touch with some solder wick and a hot iron fixed this right up.  It was relatively easy to find these shorts because the LED segment would be fully on.  Here is a quote from Mark:  “Used solder mask for first time, easier to apply paste although the thinner cross section did not reflow as well leaving numerous shorting bridges. Fixed with scalpel under microscope and retouched each lead with soldering iron to reflow.”

Using the stencil is a lot faster, but there is still a learning curve.  Here is the final picture of one of the displays being powered by the Flash machine.

Initial power on of display board

Initial power on of display board

You can see some of the debug info built into the code.  At initialization, the master card discovers the displays on the i2c bus.  It then either prints the display number that it found, or prints a 0 to indicate the display is missing.  In this case, only display 1 is plugged in, while display 2, 3, and 4 are missing so they are reported as 0 on the master control board.

The cables haven’t been finished yet, but that should happen later this week.  Pinball night is moving to Wednesday because of scheduling conflicts, so maybe we can actually run a couple of games and be able to see how many credits, and which ball the game is on.

The displays are very bright, and I think that we are both pretty happy with how they are coming out.  I’m glad that I added a voltage regulator to allow the displays to be dimmed to the appropriate level.  The mounting holes are a little bit small, so these have to be drilled out a little bit to use the original mounting hardware on the Williams game.

Hopefully another post later in the week about it working, but more than likely it will take another day or two to debug the interface to the pinball machine itself.

If anyone owns a Williams Flash game and would be willing to take pictures of their backglass, please get in touch with me.  That is the one thing that is really messed up on this game, and I want to do a translite, but the more pictures that we have, the better the translite will be.  The backglass on this machine is completely trashed, so any pictures at all would be appreciated.

4 responses to “Display boards populated

  1. Are you hand soldering? Those bridges shouldn’t happen normally, and the solder looks very dirty in those bridges.

    I suspect the problem comes down to iron temp and/or flux. With SMT I always lay down tacky paste flux (The kind you get in syringes). This holds the part in place while appying a generous amount of flux to the board. Then you can just wet the iron tip and touch the leads, the solder will naturally jump to the pad and part. This makes doing SOIC parts super easy since you can actually just drag solder each line. If something bridges just head it up and the solder mask + flux will sort it for you. Worst case add a bit of solder wick.

    It also looks like you have a HUGE cut area for your solder mask. You should shrink this to a very small area past the pads, such that there is a very large amount of it between pins. Your board house should have solder mask tolerances, use those.

    For example, here’s the tStop layer on one of my boards. http://imgur.com/3WhAGEj the white crossed out area over each pin is where solder mask isn’t applied. Note there’s still a nice chunk of it between the tiny SOIC-16 package pins, which does a lot to reduce bridges.

    • No, this is reflow soldering using a mask and a hot plate. The problem is that the part that is shown with the solder bridges is an SC-88 package. That package only has .65 mm between the centers of the pins. SOIC parts are huge in comparison at 1.27mm between centers of the pins. With reflow soldering, you assume the extra solder is going to wick up the pins and stop solder bridges from happening. The issue with the SC-88 package is that the pins are so small, that you have to have very good control on the amount of solder paste that you put on the pads. (Better control than what we actually have). Populating the boards, there were something like 14 of these parts per board, 4 boards, and Mark ended up seeing three solder bridges for all the cards. That is a pretty good percentage for that size parts. We also don’t have a great way to control the temp/consistency of the solder paste. If the paste would have been a little bit cooler, I think he would have had better luck. A little bit of solder wick got rid of the extra solder and fixed the bridge. (The pictures are taken through a microscope with 40x magnification.)

      The voltage regulator definitely should have a smaller cutout for the base of it. It should be broken into four smaller areas, but I knew that was going to be hand soldered so I didn’t really care. I agree that it needs to be fixed.

      Switching to reflow soldering from hand soldering probably saved around 60% of the time. I got the mask for free because I needed a couple masks for work and Ohararp sells Kapton in 8.5 x 11 inch sheets. I grab the unused portion for extra projects. The other nice part about reflow soldering is it naturally pulls the parts onto the pads. Even if the placement is off a bit, the solder paste will naturally try to center the parts on the pads.

  2. Where in MA are you? I just picked up a Flash with a nice BG…. and oddly enough, I’m working on a display project for it too…

    • I’m in the ‘burbs in Westford. I just got pictures of a backglass up at Pinball Wizard Arcade, but the lighting was way too dark. Mark, the actual guy that owns the Flash machine, is going to munge the pictures that he has together. He is currently out of money for the project, so I’m sort of in limbo. With the display project, I’m working on it, but slowly. I’m having problems with the i2c bus on the displays. If I would do it again, I would use a SPI bus implementation. Mark gave me all the hardware to finish it up, so probably in the next month or two, we will try to do another integration run with the actual pinball machine. (One of the difficulties is that I now live two states away from the pinball machine that I’m trying to help work on.)

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