Best practices and basic techniques used for short run SMT of boards?
ke4pjw
Posts: 1,173
I have a Propeller based project that I want bring to market. I want to do a run of about 100 of these. They will be sold as a plug n' go type of product, not a kit. It is a USB based dongle device. My prototype is compete and very solid. I am using ExpressPCB as my layout software. I have used them for other projects and have been very happy with their software and service. Everything I have done so far is thru-hole type design.
Here are some of my question...
Is there any type of good literature that describes how assembly houses do production runs? (As far as component soldering and placement)
Are there any simple or basic techniques I should know about, to best do the layout?
Does anyone have any advice to offer about doing such a project?
Thanks much!
--Terry
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Feel the need for speed between your PC's com port and Prop?
Try the FTDI 245 and the FullDuplexParallel Object.
Here are some of my question...
Is there any type of good literature that describes how assembly houses do production runs? (As far as component soldering and placement)
Are there any simple or basic techniques I should know about, to best do the layout?
Does anyone have any advice to offer about doing such a project?
Thanks much!
--Terry
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Feel the need for speed between your PC's com port and Prop?
Try the FTDI 245 and the FullDuplexParallel Object.
Comments
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- Stephen
You will probably need to budget for something like CE approval, depending on the regulations in your country. It can be expensive.
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Leon Heller
Amateur radio callsign: G1HSM
Post Edited (Leon) : 8/4/2010 4:53:14 AM GMT
This is a bit long, but actually cut very short for my potential answer.
The basics for a production house are as follows:
a) RS274X Gerber files with readme describing each file
b) Assembly DWG
c) Fab DWG
d) Excel BOM with AVL (Approved Vendor List) that contains MPNs (Manufacturer Part Numbers)
optional:
e) ASCii CAD File
f) IPC-D-356 Netlist file
g) Centroid File (X/Y data for components)
Gerber files should be of each layer in the fab makeup. For a two layer board, an example file set would include:
Top Silkscreen
Top Soldermask
Top Paste*
Top Copper
Bottom Copper
Bottom Paste*
Bottom Soldermask
Bottom Silkscreen
NCDrill File
*optional and only if PCB has SMT, but these are used by the stencil manufacturer
Basically, the assembly DWG at a minimum needs to have the solder type (tin/lead or rohs), what industry standard to be built to (IPC-610, class 2 is the typical for Propeller based product), and any special notes such as unused holes that must remain free of solder, programming/functional test required, mechanical assembly functions like heatsink hardware, etc
The fab drawing will not be necessary if you are supplying the fabs, but would contain layer stackup details, drill details, key dimensions (tooling holes, slots, etc), panelization details, copper weights, and other fab related information
The Excel BOM with AVL will provide the necessary information for the manufacturer to do two things. One, if you are having the manufacturer procure the material, this will contain the information to source the parts from distributors. Second, whether you are providing the material or not, it gives the manufacturer the ability to determine how to process certain parts. For example, some through-hole switches are not sealed so they cannot be water washed during manufacturing and the assembly house needs to know this.
I am uncertain as to what ExpressPCB provides you for assembly files, but I do know you have to purchase a gerber package from them when you need them for assembly. I would expect that they would at least supply you with a paste layer for stencil fabrication and a centroid file for machine placement.
I do actually have a project to create a sample file set that can be shared publicly so everyone can see a real life example of all of these file types and the "right" way to present them for assembly. Right now, the file set I created can only be shared with my work's customers.
~~~~~~~~~
As for the actual assembly, it depends on how your board is designed, what types of parts are on it (IE: SMT, TH, Mechanical, Wires), processing requirements (RoHS, conformal coat, testing, etc), and other details. During an RFQ (request for quote) by an assembly house, they will determine what steps the board will go through. Here are some questions that are part of the quoting process:
What's the EAU (estimated annual usage) and order size of the product
Can the SMT parts be placed by machine?
How will the SMT parts be supplied? (IE: Reel, tube, tray, cut tape, loose in a bag)
Can the assembly be washed?
Is it panelized?
Do any parts hang over the edge which limit automated assembly?
Does the board have fiducials?
Can the TH parts be waved or do they require handsoldering?
Are there special test requirements?
I could go on for a while, but I think you get the idea. This is something I go through several times a week for PCBs, cable assemblies, and mechanical assemblies at work (an electronics contract manufacturer). I have been building PCBs for 19 years now and the last 11 years have been with two CMs. I have a presentation that will cover all of this on the back burner (was supposed to be a UPEW presentation) because it comes up from time to time on various forums and I would like to share my experience.
As for the actual assembly process, send me a PM or email with more details on your board and I can write you up a DFM report (Design for Manufacturing). This will explain the processes that your board will typically go through at an assembly house and any limitations that your design will present for a manufacturer.
In regards to CE marking, most products you see with CE marking are self-certified which costs nada, so do your research before you blow off the European markets.
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Andrew Williams
WBA Consulting
PowerTwig Dual Output Power Supply Module
My Prop projects: Reverse Geo-Cache Box, Custom Metronome, Micro Plunge Logger
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Leon Heller
Amateur radio callsign: G1HSM
ps.
Terry, do not use Google for information on CE marking. The first few pages of results can be confusing and mis-leading (mostly sites with offers to help "for free" but not actually contain any real information as to how to complete the process unless you pay for the "consultation" or "course".
ec.europa.eu/enterprise/policies/single-market-goods/cemarking/
Start with the "leaflet for economic operators" PDF there.
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Andrew Williams
WBA Consulting
PowerTwig Dual Output Power Supply Module
My Prop projects: Reverse Geo-Cache Box, Custom Metronome, Micro Plunge Logger
Where I used to work we hired a facility for half a day to do our own testing (about £500), fixed any problems, and then the formal testing was just a formality. I designed their first product, the only problem was a VHF emission on the RS-232 cable, which was easily fixed with some filtering.
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Leon Heller
Amateur radio callsign: G1HSM
Post Edited (Leon) : 8/4/2010 7:56:24 PM GMT
@Leon: CE conformity should not be an issue for me as I do not intend to sell it in the EU. This will be a device that is regulated by the FCC as a 47 CFR 15 Subpart B, Class A device. I am researching if a declaration of conformity will be needed. I am sure that I can attenuate any common mode emissions fairly easily, but having to pay someone to confirm what I can test myself could be a deal breaker.
@Andrew: Wow! What a great wealth of information! I had not considered using an actual assembly house to put the project together. I just can't imagine those places being able to cater to a hobbyist sized run of boards. I will spend some time investigating what you have posted. It's really helpful to have some insight into the way the pros do this. I am sure I will have some follow up questions. Thank you!
@Stephen: That's exactly the scale of project I am looking at. The reflow toaster oven will probably be my most cost effective choice. [noparse]:)[/noparse]
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Feel the need for speed between your PC's com port and Prop?
Try the FTDI 245 and the FullDuplexParallel Object.
I'll probably be making my M44D40+ Modules with toaster oven reflow once I characterize the toaster oven with the profiler we use at work for our "real" reflow ovens. I'd like to make a controller for the oven, but so far the boards I am doing have not needed any special things to get a desired profile. Plus I still have to finish my other two active projects.
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Andrew Williams
WBA Consulting
PowerTwig Dual Output Power Supply Module
My Prop projects: Reverse Geo-Cache Box, Custom Metronome, Micro Plunge Logger
I had Screaming Circuits assemble 50 boards for me from an ExpressPCB fab. It cost more than the quote because they had to generate files, but they came back perfect, other than a couple fab flaws from ExpressPCB. 2 flaws in 50 boards, that is terrible! I've said it before: once you are at this point (thinking about assembly and more than a handful of boards), you need to drop ExpressPCB. They have issues and limit you. Once you look beyond the simple board or two and hand soldering they start costing more than buying a standalone CAD suite and using higher quality fabrication done for cheaper.
I now use the Sunstone/Screaming combo and all my boards so far have come back perfect. They also offer CE (and other) certification.
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April, 2008: when I discovered the answers to all my micro-computational-botherations!
Some of my objects:
MCP3X0X ADC Driver - Programmable Schmitt inputs, frequency reading, and more!
Simple Propeller-based Database - Making life easier and more readable for all your EEPROM storage needs.
String Manipulation Library - Don't allow strings to be the bane of the Propeller, bend them to your will!
Fast Inter-Propeller Comm - Fast communication between two propellers (1.37MB/s @100MHz)!
Regards,
Terry
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Feel the need for speed between your PC's com port and Prop?
Try the FTDI 245 and the FullDuplexParallel Object.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
April, 2008: when I discovered the answers to all my micro-computational-botherations!
Some of my objects:
MCP3X0X ADC Driver - Programmable Schmitt inputs, frequency reading, and more!
Simple Propeller-based Database - Making life easier and more readable for all your EEPROM storage needs.
String Manipulation Library - Don't allow strings to be the bane of the Propeller, bend them to your will!
Fast Inter-Propeller Comm - Fast communication between two propellers (1.37MB/s @100MHz)!
As already mentioned, the problem with ExpressPCB is when your design needs to go to the next level which requires a better price for the fab as well as design files for the assembly house. Fab houses hand out "free" software because it gets paid for by forcing you to order from them. DipTrace is just as easy as any fab house freebie software.
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Andrew Williams
WBA Consulting
PowerTwig Dual Output Power Supply Module
My Prop projects: Reverse Geo-Cache Box, Custom Metronome, Micro Plunge Logger
Rich H
I haven't used ExpressPCB but in my slight bit of experience, I have found that the over seas shops are only slightly less expensive with noticeably lower quality and longer turn around times. I don't feel the need to take jobs away from my neighbors to save a few cents per board.
Rich H
http://dorkbotpdx.org/wiki/pcb_order
This group compiles multiple orders into one large order. This entices the fab house to offer competitive prices. I've used them and the boards came back looking great!
Maybe this will help someone.
Tim
Yet again, the Parallax forum proves its value!
I'm also going to file Sunstone away in my memory for when I need large boards.
This post looks like you have shared the complete steps or process of the production house. Amazing!!!