Save money on PCB fab and how to cut the board apart with CNC mill (or table saw, press drill).

For lab geeks or hobbyist who often sends out small quantity PCB fab orders but doesn’t care about a little bit extra work, this  post will help save a decent amount of money on PCB manufacture cost by putting multiple design images on a single board. PCB fab houses usually charge a fixed amount of money per order with no regard to what is actually on the design file such as Gerber. This produces a money-saving opportunity by putting more than one design images (sometimes is also called “array”) on a single board file , and you will only be charged by just “one” order. Some PCB houses doesn’t allow this kind of thing by explicitly saying “No array allowed”. For those don’t care about this, this is actually a win-win situation because the PCB house wins your deal with no extra manufacture cost, and you save money!

If you are an Altium Desinger user, putting multiple images on a PCB design file is fairly easy. First of all, you need to have all your sub design files ready. Then, create an empty PCB and go to menu -> Place – > Embedde Board Array/Panelize. Shown in the snapshot below, you will be asked for the location of each sub design files, the size of the grid and the distance between each image. You must leave sufficient space between each images for the cutting tool to eat through. I would recommend 1/8″ ~ 1/4″ for safety, otherwise, the cutting tools are getting close enough to damage your traces.

After a couple days of anxious waiting, you receive the finished boards from the awesome PCB house, which only charged you only single order of money!

But, there comes a little bit of the extra work — you have to cut it apart before soldering the components on. I have tried different kinds of tools to cut the board apart such as table saw, press drill and CNC. All of them worked pretty well depending on different task requirements. Here are some thoughts:

  • Drill press:
    I actually never tried a press drill to mill apart the PCB board. But based on the experience from the CNC machine, I would assume that a press drill should produce pretty high accuracy if it comes with a compound table.
  • CNC:
    Undoubtedly, this incredible piece of machine produces the best ever cutting results with an accuracy of 0.0001″. It  is also capable of cutting any shape of outline if programmed properly. Here is a video clip of it:

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Extend the 3D stereo camera module of LG thrill phone P925

This is a quite interesting project which requires digging out the 3D stereo camera module from the LG thrill P925 smart phone and driving it somewhere outside the smart phone. What…? Sounds like put your eye balls miles away and… you are still able to see through them!

Is it possible?
– Of course yes, as long as you can extend the cable! Here is how I did it (with photos):

1. A brand new LG thrill P925, equipped with dual 5MP camera module that is capable of stereoscopic 3D capture:

2. Take off the back and expose the pretty big 3.7V Li-Ion battery. Use #00 Phillips-head screwdriver to avoid stripping the screws:

3. Remove the speaker module. The speaker module is actually installed on top of the middle plastic frame that is protecting the mother board and such. So it needs to go first:

4. With the speaker module being removed, it is quite easy to remove the middle frame with just a little bit efforts:

5. Under the middle frame goes the mother board and almost everything of interest. As you can see, the dual-camera module is vertically embedded into the circuit boards with FPC connector on the side. An LED flash is coming from the other side and being laid on top of the camera module, making advantage of its metal frame as heat sink. Looks like all I need to do is to dig out the camera module and then to make an extension cable for the FPC connector:

6. Flip up the flash and totally expose the camera module:

7. Pull out the camera module from its bed. This requires some efforts as the module is taped on its bottom and the outline fits the bed pretty tight.

8. Gently disconnect the FPC connector from the mother board and the camera module is completely separated:

9. Now I am facing the real challenge: how to make a cable with the connectors that mate with the ones on the phone mother board and the camera module. With some measurements, it is not difficult to find out that it’s a 40-pin, 0.4mm-pitch connector.  If Digikey or some components distributor would carry the same products, things would be much easier. Unfortunately they don’t. I ordered all the available 40-pin, 0.4mm-pitch connectors but none of them fit the cell phone. After talking to the LG phone repair shop, I finally figured out its connector is “GB042-40S-H10-E3000” from LG. Apparently, this component is not that easy to get hold of.

Since it is almost impossible to buy the mating connectors, the next possible approach is to replace the original connectors with the ones available from Digikey. So I ordered several pairs of the connectors “DF40C-40DP-0.4V(51)” and “DF40C-40DS-0.4V(51)” from Digikey. Both are manufactured by Hirose.

10. Replacing the 40-pin, 0.4mm-pitch connector is not non-trivial job. It requires some desoldering / soldering skills. I strongly recommend Chip Quick’s Removal Package “SMD1” for components removing. Here is the photo of the LG thrill when the camera module connector is remove from its mother board:

11. A closer look at the solder pad. Although I was doing this with extreme care, I still mistakenly wiped out one pad. I was just lucky as I later on figured out that this pin is for ground so it was fixable by jumping a wire to some nearby ground.

12. Soldering a new connector is considerably easier than removing. Here is the photo and a closer look when it is done:

13. Now the mother board has a new connector, so should the camera module.

14.When both sides have been upgraded with the new connectors, a function test should be carried out before I move on to the cable part. Simply plug in the camera module back into the new socket and turn on the cell phone. Make sure everything still works after the replacement procedure.

Next step towards the final “extension” goal is to literally make the extension cable. The FPC cable tailing on the camera module would be an ideal solution for the extension, but the cost is going to be an issue. For this prototype, I decided to make low cost circuit boards as the adapter.

Adapter board for camera module:

Adapter board for mother board:

15. Solder connectors on the mother board side adapter, and the finished board looks like:

16. After the adapter is finished, plug into the mother board and tighten the screws to the phone body. Since the PCB is little big, I had to trim off the inner plastic frame to make it fit. White cables are 0.5mm-pitch, 20-conductor FPC jumper ordered from Arrow. FPC BackFlip™, Easy-On™ connectors are from Digikey.

17. Then finish the camera-side adapter. The vertical FPC connectors are from Digikey. As shown on the left side of the picture below, there are a series of bypass capacitors being mounted close to the camera connector. These bypass capacitors are critical for the extension to work since the camera module is a high-speed digital device requiring large current to switch between logic low and high at high frequency. Bypass capacitors work as energy storage to supply the surging current and avoid voltage drop, which will cause the device failure. When the camera module is extended away from the mother board, it also leaves its “energy storage” on the mother board. So some local bypass capacitors are required on the adapter board.

18. Everything is ready for the final assembly. Make sure cables are connected tightly and turn on the phone. The camera module is working outside the body now!

Here is the final application for this project:

A Cell Phone Based Platform for Facial Performance Capture. (http://gl.ict.usc.edu/Research/CellHeadCam/)