Daniel - see below, and good luck with the report. Peter Daniel Themann <[log in to unmask]> 15/08/2002 06:30 AM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to themandj To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: [TN] Smoke Detector Circuit Board Dear List, I recently contacted the Australian Surface Mount and Circuit Board Association with some technical questions relating to PCB manufacturing, but their instructors are currently traveling and Dianne Hunt recommended that I contact Technet. I am a student at the University of Cincinnati and my teammate and I must write a report describing in detail how a circuit board is manufactured. I recognize that you are certainly not employed to assist college students with technical questions, but if you have a moment and could address the following points without too much trouble, I would very much appreciate your help. Our circuit board comes from a smoke detector and is approximately 1.5 $B!I (B by 3.5 $B!I (B. It contains both surface mount (resistors, capacitors, etc.) and through- hole components (ionization chamber, electric horn, battery contacts, etc.). These components are placed on ONE SIDE ONLY. We have tentatively drawn up the following process steps. 1. Screen Print Solder Paste on side one **OK** 2. Place surface mount components on side one **OK** 3. Dry paste **No! - drying the paste will remove the volatiles from the flux and wreck the wetting action. Boards should be reflow soldered as soon after component placement as possible (without drying)to minimise solderability problems.** 4. Reflow Solder **OK, but if using water-soluble flux, boards should be cleaned here to remove residues ASAP before they harden. You would probably be using no-clean, though, on a smoke detector board** 5. Insert through hole components on side one **OK** 6. Invert Board and apply adhesive on side two **What purpose does adhesive serve when, from your description, there is nothing on side two?** 7. Wave solder **OK. You might want to consider clinching or half-clinching two diametrically opposing leads beforehand to prevent components rising out of the board on the wave. There are other component-holding techniques as well to prevent this happening. **Less likely on something like a smoke detector board, mask any empty component holes on the solder side of the board (side 2) where there are component shortages or modification options. This prevents the wave filling them with solder, if you want to use these holes later. For something as commercial as smoke detector boards, you wouldn't build with component shortages, or modify them once built, as this is more trouble and cost than it's worth, and masking is an additional operation that's also additional cost and time.** 8. Final Clean **OK** **9. De-panelise.** Question 1. Does the process described above seem reasonable? In particular, is step 6 necessary if all components are applied to one side only? **See above** Question 2. What type of batch sizes would be reasonable in $B!H (Blow volume $B!I (B and in $B!H (Bhigh volume $B!I (B processes for a board of this type and size? **I'm in the Aerospace industry where all our products are considered "low volume" - typically anywhere between 1 or 2 for prototypes and 50 units for entire production runs. "High volume" depends on your line set-up, whether you work shifts or around the clock, and how many component sets your machines can handle before they need to be re-loaded - in other words, the resources you have at your disposal to do the job and if they're shared with other jobs or not. Also the solder paste stencil will need to be cleaned every few prints (could be automatic), and fresh paste added (could also be automatic). Dream-up the sort of assembly line that could make this board, add in any limitations you like (lack of people, the line is needed two days a week for another job, the people only work 9-5, etc., then use the set-up to explain any economic batch size you think of. Typically it will be a case of how many boards do you want to build, or how many boards can you process in a working day, given all the process run times, time for documenting the progress of the job. Bear in mind that one board panel does not have to be complete before the next one starts. ** Question 3. What would be approximate setup and run times for each process? We need these times both for our process route sheets and as input into our cost analysis. ** Aerospace product processes tend to be slower than high-volume commercial stuff because there isn't the same commercial urgency or to deliver lots of product to an eager population of consumers. More care has to be taken, and the High-volume machinery is more expensive in general than low volume stuff, which is therefore less efficient (i.e. slower). So use my answers as a guide only and hope that someone in the mass production arena can give you more accurate info. ** **Solder paste printing - maybe half an hour to fit the stencil to the printer, do a test print and inspect it for height, coverage and accuracy. Run time per panel of boards (they're probably panelised until removed after the last operation, rather than being individual boards)is maybe 1 to 2 minutes. **P&P - If this is a first ever run, a Pick & Place programme will have to be created from the Neutral file information in the Gerber data (Gerber data digitally describes every feature the PCB, including the component layouts, sizes orientations and location on the board). For a small, simple, board, this might take an hour to do and check. Component loading and checking to the P&P machine - for such a small board, maybe 1-1.5 hours to fit components to feeders, load feeders and check loading is correct and load up the placement programme. Add another half hour or so if you want do a confirmatory run and inspect it for alignment, placement and so on (called an FAI (First Article Inspection) run where a bare board is covered with sticky plactic sheet (sticky side outwards) and the components populated onto the adhesive. This is then inspected manually or using AOI machine for correct placement/non-placement, orientation, alignment and so on). Population of a panel of boards with SMT parts is probably 1 to 2 minutes** **Wave solder - fitting boards to conveyor frame, setting up the conveyor speed, setting pre-heater temperature, wave height and so on, is maybe half an hour if parameters are known. Maybe half a day to establish all the parameters if the board run is the first ever of its type. Cycle time is about 5-7 mins. once the parameters are known and set. **Cleaning - fairly standard process with no specific set-up. Cycle time is about 10 minutes, and if using water wash, maybe half an hour in an oven to dry the boards afterwards. Question 4. Is it possible to purchase the board itself (without the components attached) from an outside vendor and to simply attach the components in-house? Or does the manufacture of the board and the soldering processes by which the components are attached constitute one continuous process? If the board itself can be purchased outside, how much might it cost given low and high volumes? **PCB's are normally fabricated by a specialist company for population by its customer. There are companies, though, that offer a "turn-key" service - i.e. they will take charge of having the PCB made, the components bought and the whole lot assembled and tested for you. All you have to do is to supply them with the relevant drawings and parts lists. This is an option if you have no assembly facilities yourself, and depends on relative economics (i.e. it's cheaper to subcontract everything rather than invest in the process machinery yourself). In short, fabrication houses specialise in producing bare boards and assembly shops specialise in mounting components to the bare boards. Usually, these specialisations are separate trading entities.** Question 5. Does you know of any companies that manufacture special through- hole components such as the electric horn and the ionization chamber? Do you know where prices on such components, and more common components such as resistors and capacitors, could be obtained? **No, but for normal components, you can find any number of component distributor on the Net. You can probably find your Horn and Chamber people there too, if you put in the right key search words.** If you could spare us a few minutes of your time we would be most grateful. If you feel that you can assist with some questions, but not with others we would still appreciate any insights you can offer. If you know of anyone else who might be able to help, please feel free to forward this message on. The project is due in less than two weeks so timely responses would be fantastic. Thank you in advance for your help. Sincerely, Daniel Themann Arthur Jackson **Short of actually writing the report for you, I'll try to help with any other questions you may have (time permitting), unless you acquire a guru with more relevant experience to help you. You've just put your toe into a very large, very deep and very murky pond, though - such is the world of electronics manufacturing. Good luck. If you get an A*, you'll owe us a beer! Peter --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 --------------------------------------------------------------------------------- [This e-mail is confidential and may also be privileged. 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