#127 - design for manufacture - Page 1
Forum section: electronics / general

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 15, 2010, 12:46:40 pm
content: A few comments...Assemblers hate tubes, as they take time to load, and picking can be unreliable (and they can be put in backwards) - some places will re-reel tubed ICs to reduce downtime on the P&P machine - Get SOICs on tape wherever possible - sometimes this is a choice between manufacturers for similar parts (e.g. 74HC logic, voltage regulators etc.).Device programming - it's rarely true that manufacturers prefer to program on-board unless there is already some testing going on that needs a pogo-pin jig etc. They will usually use external programming companies who will program devices (some will also source parts, and their bulk-buying power may cover all or part of the programming cost) , as well as mark & re-reel for very little cost - pennies per part. There will be a setup cost so you need to be into a few hundred before this is viable.Microchip have a very cheap and flexible programming service, so you can set up your own part numbers, and then buy ready-programmed parts, labelled/marked and packaged as you specify. I think you can also set it up so your assembly house can be authorised to order your preprogrammed parts if they are sourcing other parts as well. Another benefit of the Microchip service is you can get parts reeled at lower quantites than you can buy blank parts on reel, to avoid using tubes.Panelisation - if your PCB is rectangular, it is usually cheaper to do a V-scored panel instead of routing unless you need the smooth sides, as there is less wastage (smaller overall panel size due to no gaps), and breakout takes less effort than breaking out tabbed boards. A panel with lots of small PCBs can take a lot of time (i.e. cost) to break out. If you do use tabs, put them on the edges, not the corners (as shown on Dave's example) , as depanelising toolslike this manual oneneed space for the blade either side. Powered versions of these are also commonly used - ask your assembler what clearance and rout width they need for their depanelising equipment.Similarly on odd-shaped PCBs, think about where to put the tabs to allow access to a tool - for curved PCBs you may need to add extra rout-outs into the waste to allow the straight blade to get in there.If you have parts that overhang the PCB edge (e.g. USB sockets), remember that this will overhang an adjacent PCB in the panel!Fiducials - it's a good idea to make these not symmetrical about the panel, so if the board is loaded the wrong way round the fid check will fail to alert the operator.Gold plating - another benefit of gold, especially on proto and hand-assembled PCBs is that the colour contrast against the silver of solder makes it very easy to spot non-soldered joints, or where paste is inadequate.Another general point - make your PCB as small as you can - the PCBs will be cheaper, and if you can get more on a panel this will reduce assembly cost. With odd-shaped PCBs, consider how efficiently they will panelise, and adjust if needed.Many assemblers keep common stock parts, e.g. 10K resistors, 100n caps permanently loaded on machines - ask them about this. Also, if they are buying parts for multiple customers there may be some savings to be made getting them to source parts instead of supplying them with kits.When sending them a kit of parts, if the parts are expensive enough to not justify a full reel, you need to include spares to cover the wastage due to the take-up and trailer their machines need - typically a minimum of 6 inches, plus a few percent to cover mis-picks. Label any particularly expensive parts & ask them to keep any that come out during loading or rejected during assembly - P&P machines can typically be programmed to place rejected parts in specific bins.If you get a part-reel back from an assembler DO NOT cut off the loose cover tape & empty part of the tape, as this is used to thread-up the reel next time - if you cut it, you'll lose a few inches worth of parts next time.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: November 15, 2010, 04:02:32 pm
content: That was a very interesting video which opened my eyes! Thanks for that, Dave!From my limited experience of PCB design ( I built my own bench PSU using home etched boards from an Electronics World article several years ago ) I can appreciate just how much attention to detail one needs to get the boards populated! Never mind for volume production!

author: allanw
author_rank: Frequent Contributor
timestamp: November 15, 2010, 07:31:26 pm
content: Thanks Mike, good tips as well.I wish I picked gold plating for my last batch of PCB's. It would have been only $4 more and it would have looked much cooler.

author: Psi
author_rank: Super Contributor
timestamp: November 16, 2010, 01:19:00 am
content: i must say, that was a very useful and interesting video

author: .o:0|O|0:o.
author_rank: Regular Contributor
timestamp: November 18, 2010, 03:53:53 am
content: Excellent video! Just got around to watching it and learned a great deal. Can't wait to produce my own at some stage. A while ago I came across Dave's PCB eBook; I don't have the link right now but I think it would be worth linking to it ......So a "mil" is a "thou", but not a "millimeter". I can see how that little detail might cause people a lot of trouble..o:0|O|0:o.

author: DJPhil
author_rank: Frequent Contributor
timestamp: November 18, 2010, 07:32:22 am
content: Quote from: .o:0|O|0:o. on November 18, 2010, 03:53:53 amHere ya go.

author: tyblu
author_rank: Frequent Contributor
timestamp: November 18, 2010, 01:45:25 pm
content: Great video - I enjoyed it! Those are some sexy boards, too.Thanks.

author: thakidd
author_rank: Regular Contributor
timestamp: November 20, 2010, 06:51:44 am
content: Dave, loved the video. Very informative as I have never taken anything to that scale.I wondered, what software was used for the development? Was that Eagle? If so I need to upgrade.Also a question specifically to Dave: When you need to do a one off before you take it to a pick-and-place or pcb mfg, what method do you use if you need to make a board right in the shop?

author: armandas
author_rank: Frequent Contributor
timestamp: November 20, 2010, 12:39:46 pm
content: Great video, Dave, thanks!I've got a couple of questions regarding the PCB design.1. Should mounting holes be connected to the ground? If the circuit/case is earthed, I'd assume the mounting holes would be connected to the earth? What should be done when there is no earth connection? What if the screws are exposed and can be touched by the user (I'm talking about low-voltage stuff, so not a safety issue)?2. Allan shared some pictures of theinsides of Tektronix DPO4034scope. Just wondering what the squares (see attachment) are for?

author: armandas
author_rank: Frequent Contributor
timestamp: November 20, 2010, 12:42:34 pm
content: Quote from: thakidd on November 20, 2010, 06:51:44 amIf you're talking about the software in the video, it was A!tium Designer (replace ! with L)

author: jahonen
author_rank: Super Contributor
timestamp: November 20, 2010, 12:54:35 pm
content: Quote from: armandas on November 20, 2010, 12:39:46 pmScrew connection is often an EMC and ground loop issue. The best connection should be considered from that perspective. Behaviour on ESD and emission perspective should be considered. AC connection to the chassis is often used, as it prevents low-frequency loops but retains high frequency grounding.The squares are balancing features added by the PCB manufacturer, to get better copper distribution during copper growth/etch process. Large void areas are difficult to grow/etch copper evenly, so manufacturers often add extra copper to void areas, if design otherwise permits.Regards,Janne

author: allanw
author_rank: Frequent Contributor
timestamp: November 20, 2010, 03:34:34 pm
content: Quote from: jahonen on November 20, 2010, 12:54:35 pmI notice in multi-layer boards that the top and bottom layers do not have ground pours like a 2-layer board would. Why not?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 20, 2010, 03:54:41 pm
content: I am against the idea " Build anything in SMD (SMT ) .1)They are not repairable.2)The damaged board gets trashed , with many good parts on it. ( wasted materials)3)No the SMD repairs , even today they are not the widest known method.The throe-hole design rules even today , at any corner of our planet.4)Since when the production cost rules over anything.( Its possibly just me, disagreeing here, but I had to say my rant ... )

author: armandas
author_rank: Frequent Contributor
timestamp: November 20, 2010, 04:05:07 pm
content: Quote from: jahonen on November 20, 2010, 12:54:35 pmI guess it's time to go read some stuff on Compliance Club website.Quote from: jahonen on November 20, 2010, 12:54:35 pmHm, I thought copper balancing was the thing of the past..Quote from: allanw on November 20, 2010, 03:34:34 pmI've read that it's a matter of preference. When you have power and ground planes, there is no need to have pours on the outer layers. The etched copper can be recovered and you don't have to worry about stiching.

author: Unknown
author_rank: Unknown
timestamp: November 20, 2010, 04:09:15 pm
content: Quote from: Kiriakos-GR on November 20, 2010, 03:54:41 pmUnless you're competent. Desoldering through-hole components with lots of pins is without damage much harder than SMT. No risk of pulling out plating from multi-layer PCB's with SMT, and less heat is needed. Not to say that through-hole is impossible, but it's definitely harder than applying some hot air.Quote from: Kiriakos-GR on November 20, 2010, 03:54:41 pmThat's just a trade-off of rework costs vs. materials, plenty of through-hole designs aren't repaired either, since most through-hole designs these days are cheap crap (except power electronics, obviously).Quote from: Kiriakos-GR on November 20, 2010, 03:54:41 pmPlenty of places do cell-phone repair, it's not like SMT rework is a rare skill.Quote from: Kiriakos-GR on November 20, 2010, 03:54:41 pmHow many high-quality through-hole designs were made in the last fifteen years? Yes, sometimes older stuff is better, but usually not. Without SMT, our cell phones, cameras, MP3 players, laptops and other portable electronics would be a lot larger, less powerful and more expensive. If you want to use any modern components, you're usually limited to SMT. Try to find a modern 32-bit MCU or FPGA in through-hole!Quote from: Kiriakos-GR on November 20, 2010, 03:54:41 pmIt does not, it's a trade-off between costs and benefits. Expected returns and sales are also factored into this. But it's not like you would sell a lot more iPad's if it were through-hole, or that it would be anymore reliable.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 20, 2010, 05:14:29 pm
content: My rant was targeting electronic designs for industrial use.And another point that probably got missed ( I watched only the half video..)Must be the consideration about hazardous materials on the PCB, and recycling.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 20, 2010, 07:25:33 pm
content: even big companies have to keep up with the latest tech, otherwise they'll lose or simply dissapear. recently i tried to fix through hole component/board and it turned out to be pain in the arse, not the usual thing that i had, i had couple of experience of this kind. the pcb hole just barely fit the TH component leg, simply sucking the solder wont do it, i have to use screwdriver and plier to take the component out. let it be in smd (resistor), it will just a matter of secs to poke that one out with two irons. btw, i still in failure downloading the full Dave's vidzand my BW is in jeopardized

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: November 20, 2010, 07:51:01 pm
content: The serviceable through hole PCB , it had to be made with high quality PCB, so to be able to "take" abuse.Unfortunately , the last time that I have seen it, was on some old televisions made in Germany,and in the Fluke 80XX DMM's .

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 23, 2010, 03:20:15 pm
content: Quote from: alm on November 20, 2010, 04:09:15 pmIntel and AMD have been making through hole 32 bit and 64 bit CPUs until recently.I have learned to work with SMD (smallest I have done is a Flash chip in a USB Flash drive) and understand that it is the way the future is going. (I mostly work on power electronics, where the big stuff will always be through hole or at least large footprint SMD.)I'm sure that back in the days when tubes and discrete semiconductors were the norm, some complained about the tightness of the DIP package.

author: scrat
author_rank: Frequent Contributor
timestamp: November 23, 2010, 05:02:25 pm
content: Quote from: DJPhil on November 18, 2010, 07:32:22 amI have read and appreciated it one or two years ago, when I didn't know who that David L. Jones was.Now that I know him, if I will have read it but not the author's name, I'll probably have recognized the style

author: EEVblog
author_rank: Unknown
timestamp: November 23, 2010, 11:39:21 pm
content: Quote from: scrat on November 23, 2010, 05:02:25 pmI was never really happy with that tutorial, it was just thrown together on a weekend as an article in Silicon Chip mag after I perhaps foolishly said to Leo Simpson that I recon I could write an article on PCB design.I subsequently released the PDF version and it's just been ridiculously popular since then. The number of downloads is into the hundreds of thousands.Was always meaning to update and expand it, but never got around to it.Dave.

author: slburris
author_rank: Frequent Contributor
timestamp: November 24, 2010, 04:19:55 am
content: RE: SMD partsI'm finding I actually prefer to design with SMD parts these days. Not thatI enjoy hand soldering 208 pin TQFPs, but I really hate havingto form the leads, flip the board over, solder, clip the leads, repeat.I recently completed building the all transistor clock:http://transistorclock.com/and I'm still finding clipped leads all over my electronics area!About the only through hole components I go out of my way to useare LED displays, because then I know the alignment is perfect.I'd find that very hard to do with SMD displays. Until the hobbyistpick and place machine comes about, that is :-)Scott