Werner, This sounds like a NO MORE EXCUSES manifesto to me. Thanks, ya done good. --- Ron K. Jeffries @ronkjeffries
On Mon, Feb 7, 2011 at 07:08, Werner Almesberger <[email protected]>wrote: > Here are a few more thoughts about the Universal Breakout Board: > > http://downloads.qi-hardware.com/people/werner/ubb/ubb.jpg > > Since several people have expressed interest in manufacturing UBBs, > I discuss the industrial production process at the end. > > > Motivation > ---------- > > My motivation for making it was a) because I needed something like > it for the atusb project, and b) because I think we're not seeing > enough use of the Ben's 8:10 card slot. > > Let me give a bit of background one the latter point. Back when > Rikard "discovered" the 8:10 card slot, we talked a lot about how > access to it could be made convenient. > > One idea was to make a extension cable that would end in a 100 mil > header that could then plug into a development board. Wolfgang had > a few of these made in China as a "street job". This picture shows > one, minus the 100 mil header: > > http://en.qi-hardware.com/wiki/File:Rfm12_microsd.jpg > > Alas, not much happened beyond this. I think part of the problem is > that there are many different ways in which one may want to connect > something to the Ben, and a 100 mil header, although popular and > versatile, may not always be desirable. > > Another issue is that, while the extension cable is simple, turning > this into a proper product that can be made in quantity at a > reasonable price and with good quality would be more time-consuming > and more expensive than one may expect. > > UBB dodges the issue of how to connect at the other end (more about > this below), and addresses only the problem of getting the signals > out of the Ben. Specifically, > > - UBB provides the non-trivial electromechanical interface to the > Ben's 8:10 slot, but > > - it is the user/customer's responsibility to design a connection > suitable for their needs, and > > - it is also the user's responsibility to implement that > connection and to verify its function. > > UBB should be easy to manufacture and "productize" in general. (More > about this later, too.) > > > For whom ? > ---------- > > I see the use of UBB mainly in three areas: first, to make the Ben > more popular as a "master" for circuit development, be this for > hobbyists or professionally. The master would typically be a > placeholder for some other device that connects in the final design > or that may even be embedded in it, but the master may also perform > temporary tasks, such as in-system programming and acting as a > debugging aid. > > Second, similar to the "master" role, aid in experiments where only a > partial circuit is made, with the objective of examining certain > properties of acting as a tool with a limited lifetime, but where > this circuit is not intended to become part of a "finished" device. > > For such experiments, it's important to have a flexible "master" > device. A small Linux system that can connect directly into the > circuit while providing all the usual tools and infrastructure is > ideal. > > Third, lower the bar for experiments with extension circuits designed > for the Ben. Such circuits could later become proper 8:10 cards or > they could even be integrated into future NanoNote products. > > > The ribbon cable > ---------------- > > I picked a ribbon cable, because these cable are easy to obtain > anywhere and they are quite versatile. Here are a few examples > that illustrate possible uses in combination with ribbon cables: > > First of all, there are convenient press-fit connectors for them, > like the ones used for old (PATA) IDE cables: > > http://downloads.qi-hardware.com/people/werner/ubb/use/hdr-f-pres.jpg > > The picture shows a connector with ten contacts. UBB has only eight, > but while connectors and even cables of this shape with only eight > contacts do exist [1, 2], they are not very common. It is easier to > use a cable with ten signals and just cut off the two unused ones > after the connector. (And to reserve a bit of extra space where the > connector attaches.) > > One can also solder the wires individually, e.g., in this type of > connector (for 100 mil headers): > > http://downloads.qi-hardware.com/people/werner/ubb/use/sil-conn-f.jpg > > It's of course possible to solder the cable directly to a circuit, > like I've done with the atusb I'm currently working on: > > > http://downloads.qi-hardware.com/people/werner/wpan/tmp/atusb-20110131-bench.jpg > > Or maybe to an adapter board: > > http://downloads.qi-hardware.com/people/werner/ubb/use/dil-adapter.jpg > > Or with a custom-made PCB like one of these, which allows to apply at > both ends the approach of directly attaching the ribbon cable to the > board: > > http://gallery.slashhome.se/main.php?g2_itemId=4881 > > http://downloads.qi-hardware.com/people/werner/wpan/tmp/atusb-pgm-20110203.jpg > http://downloads.qi-hardware.com/people/werner/f32x/c2ben-run1.jpg > > For the nostalgically inclined, there are also press-fit connectors > in the shape of DIP IC packages: > > http://downloads.qi-hardware.com/people/werner/ubb/use/dil-conn.jpg > > Another non-permanent way of connecting things is with probe clips: > > http://downloads.qi-hardware.com/people/werner/ubb/use/clips.jpg > > And so on. > > > The anatomy of UBB > ------------------ > > The following drawing shows the various zones of the UBB board: > > http://downloads.qi-hardware.com/people/werner/ubb/zones.pdf > > From right to left: > > - Permanently inserted: when the board is in use, this area remains > permanently inside the Ben's 8:10 card slot. > > - Temporarily inserted: when pushing the card to insert or remove it, > this part of the card is pushed into the Ben. While the card is > inserted, this area stays outside the case and forms a small gap. > > This 1.4 mm gap can be seen on cards that have an outside part > that's wider than the inserted part, e.g., the UART board: > > http://downloads.qi-hardware.com/people/werner/uart/pix/uart-inserted.jpg > > The gap is marked in UBB with a small indentations at each end. > These indentations only serve as markers and have no other > function. > > - Coating overshoot: when coating the contacts with silicone or some > other isolating material, the coating has to terminate within this > 1.5 mm wide area. Transparent coatings can seen in this picture: > > http://downloads.qi-hardware.com/people/werner/f32x/c2ben-run1.jpg > > - Cable contacts: this is where the bare wire ends get soldered to the > exposed contact pads. > > - Cable landing: this is a 5 mm wide space to which the cable can be > glued. Attaching the cable with glue ensure that the wires and the > pads remain in a fixed position relative to each other and makes it > easy to solder them. > > For the best soldering results, one should first tin the wires and > then gently bend them down, towards the pads. The following kind of > tool works great for removing the isolation from the ribbon cable > ends: > > http://downloads.qi-hardware.com/people/werner/ubb/cable-stripper.jpg > http://downloads.qi-hardware.com/people/werner/ubb/strip-ribbon.jpg > > > Industrially producing UBB > -------------------------- > > The following areas need to be considered when taking UBB to a PCB > fab: > > - the board material, > > - the Gerbers that define what goes onto the boards (copper, solder > mask, silk screen), > > - the cutting of the board, > > - and panelization. > > Below are a few explanations that should help to obtain the desired > results. > > Disclaimer: I haven't interacted with a PCB house myself yet, so all > this is based on theory and on second hand knowledge. > > > The PCB is 0.8 mm (1/32") FR4 with 1 oz copper on each side. The > surface finish would ideally be gold (ENIG), but tin-plating may be > acceptable. Note that gold-plating, while sounding like something > expensive, may not add significantly to the overall board cost. > > There is one plated through-hole (PTH) via. The via hole has a > diameter of 10 mil, but this can be changed to larger or smaller > values if necessary. > > Solder mask can and should be applied for appearance and to make it > easier to solder the ribbon cable. (It's okay if the solder mask is > scratched during use.) A silk screen should be applied. > > > When generating Gerbers, at least the following layers are needed to > produce the board: Front, Back, Mask_Front, and PCB_Edges. > > SilkS_Front (front silk screen) is strongly recommended - it contains > labels, the project name, "qi-hw.com", and the license (CC-BY-SA). > > The Comments layer is optional and probably best avoided. It has > meaningful content if merged into the silk screen, but makes the board > look a little crowded. Note that it also contains a drawing that's > outside the board. > > Mask_Back is optional (it's empty - the back is just one large ground > plane). > > There are two potential pitfalls when generating Gerbers with KiCad's > pcbnew: > > - the ground zone at the back may not be filled. To make sure it's up > to date, either run the DRC or "Fill or Refill All Zones" > > - make sure to check "Exclude pcb edge layer" in the plot dialog. > Otherwise, the board outline is placed on all layers, including the > copper layers, leaving a ~2.5 mil path of thin copper around the > edge. This may not only look odd, but could also cause trouble if > shorn off. > > For reference, I've uploaded the latest Gerbers as > > http://downloads.qi-hardware.com/people/werner/ubb/ubb-gerbers-20110207.tar.gz > > I recommend using "gerbv" to view Gerber files. > > > The board geometry has to be fairly precise. Tolerances of up to > +/- 0.1 mm are probably acceptable, but more accuracy is better. > Here are the general dimensions of an 8:10 card (all in millimeters): > > http://downloads.qi-hardware.com/people/werner/ubb/8_10-card.pdf > > The board outline is specified in the PCB_Edges layer with a 5 mil > line whose center (!) is where the physical board edge should be. > The following drawing illustrates this: > > http://downloads.qi-hardware.com/people/werner/wpan/tmp/top.pdf > > The yellow line is the board outline as drawn in the layout. The > expected actual board surface is shown with black stripes. Here is > a side view showing how the cutting tool has to be offset to obtain > the desired result (not to scale): > > http://downloads.qi-hardware.com/people/werner/wpan/tmp/edge.pdf > > In case the PCB house is unable to generate correct toolpaths with the > data provided, I can also perform the offset calculation according to > their tool specification. > > The board needs an edge that falls off sharply. V-scoring would almost > certainly yield undesirable mechanical properties and/or require > extensive manual post-processing. > > > Since the UBB board is small, multiple UBBs should be made from a > single board. For this, the UBBs have to be arranged in an array, > according to the specifications provided by the PCB factory. If the > PCB fab can do this themselves, even better. > > If the PCB fab cannot produce a cut that goes all around the UBB board, > it needs to remain attached at some point to the original PCB. This is > often done with a perforated bridge that is later broken off. The > following drawing shows which areas of UBB are more or less suitable > for placing such bridges: > > http://downloads.qi-hardware.com/people/werner/wpan/tmp/edge.pdf > > The red zone should be avoided, because it would be difficult to > remove any remains of the bridge. The yellow zone is easier to handle. > The green zone does not need cleaning. > > > [1] > http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=609-3570-ND > [2] > http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MD08R-100-ND > > - Werner > > _______________________________________________ > Qi Hardware Discussion List > Mail to list (members only): [email protected] > Subscribe or Unsubscribe: > http://lists.en.qi-hardware.com/mailman/listinfo/discussion >
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