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Emails about electronics manufacturing


Date:    20010108
From:    Bob Paddock <bpaddock@csonline.net>
To:      Multiple recipients of the Chipdir Mailing List
Subject: Re: Manufacturing questions

I have a question about electronics manufacturing. I may need to arrange to manufacture some quantity (10K to 50K units) of a design, but not having dealt with this quantity before I am unfamiliar with the services that are available.

Some places only deal in large volumes, some places only deal in small volumes, there can be different issues.

I know that Semions (sp?)/Infinion has a contract division that does volume stuff.

I work for a company that does the lower volume stuff, generally under runs of 5000, this is written from that perspective. www.matric.com/

Can anyone recommend references on the processes involved or some firms that do this sort of work (PCB assembly)?

Do they like to receive PCBs and parts and perform the assembly, or will they source these themselves?

It is usually better to let the contract house to source their own parts. They will buy a far higher volume worth of parts than you alone will.

If there are parts that are unique to your job then you should supply them.

Doing a 'kit' of parts always cause problems with stuff that is out of date, especially firmware issues.

What mechanical requirements exist for the PCB to make assembly easier for pick and place machines or any other processes that might be used?

Spacing to allow for the flying heads to 'fit', not all that much. The foot prints of the parts are more important to get proper solder flow. There are also issues of placing proper targets for the test equipment.

Its a 50/50 call on if it is better to let the contractor do the PCB layout (they will charge you for this) or you supply it. The both have there advantages and problems.

If the contractor does it, you can be sure it will fit their equipment, but maybe you have 'noise' issues or RF issues where your own layout would be better. Some melding of the two are the best option.

What sort of cost might I be looking at for placing the parts, soldering (wave or reflow process)?

This is actually the smallest part of a contract job, which surprises most people, see below for details.

Can the firm that does assembly advise me on these points?

The good ones can, if they can't move on, as it is in their best interest to help you. However some places do charge for doing 'Request For Quotes', its mostly a issue of paying for the time.

Any advice would be appreciated.

This is a insider view of why things cost so much:

The first item to consider is how well put together is your design package. Does your Bill of Material specify parts fully? For example I was given a BOM that said "C1 Capacitor". The customer got mad when I asked what value it was. It should tell me the value, the tolerance, the voltage. If there is a existing PCB layout it needs to give me a exact foot print, or a industry standard reference. Do you require a exact part (higher cost) for some reason like approval issues UL, FCC, MSHA etc, or can I use what I already stock (costs are lower because I buy by the tens-of-thousands a month).

A simple .1uF cap can cause problems if your approval paper work says its a purple-one for example, and we use a blue one (inspectors want thing to LOOK EXACTLY THE SAME), or maybe it doesn't matter at all for this application, you need to document issues like this.

Do you have full design prints that show complete parts layout, a good schematic? If not I'll have to draw them, this takes time and costs. Just because YOU know where the parts go, doesn't mean that the person building it for you does. A schematic is not required to simply build the boards but if you want us to test them then it is.

Is there any regulatory issues that need dealt with? Do we have to seek FCC Part 15 for you?

Its your design, we just build it, but when it doesn't work, it always seems to be 'our fault'. We do look for obvious problems, but some customers get mad when we point out problems. Do you want us to test it once it is built? This takes our time. Do you have a test fixture that you can supply or do we have to design and build it?

Does your board 'fit' our equipment? For example, to go on the automated test line you need to have references targets on the PCB for alignment. If there are no alignment references things get done by hand, taking more time, raising the cost.

Is the board SMT? If so we need to have a paste stencil made at a costs up to $500 for large boards. We pass this on to you. There are other setup fees that may come up depending on the job. Does your part spacing allow clearance for the flying 'head' that places the parts?

Does your job require us to get tools or equipment that we might not have? Frequently we will eat this cost, but if it seems likely that you are the only job that will ever need it, then we pass this on to you.

The stuffing of the boards is usually the smallest part of the time, it is the up front setup, and tear down items that take time, testing and documentation that drives up the costs.

As you can see there are many places where time must be spent, that generally get over looked when you are 'doing it your self', because you consider your time 'free'.

For comparing companies you need to find out their policies on giving you quotes. Do they charge for this? Some do, some don't, we decided on a case by case bases. We usually have some up front one time fee to cover the one shot items, SMT stencils for example, but some companies 'hide' these costs by raising the cost per board.

We've had people leave us "because you cost to much" only to return after a time saying "we got what we paid for". Keep this in mind if nothing else.

For locating companies in your region, start by asking at your local computer store, vocational school/technical collage, or Amateur Radio Club. There will be a person some place at one of them that can point you in the right place.

You might also want to look up "The American Contract Show" organization that puts on regional shows every year:
www.amcomshows.com/

Bob Paddock


Date:    20010109
From:    Bob Smith
To:      Multiple recipients of Chipdir Mailing List
Subject: Re: Manufacturing questions

Bob Paddock gives good advice, but I have only a couple of things to add:

  1. It is generally better to let the assembly house source all common parts because, for automatic insertion, the parts must be bought in the correct packaging to fit their equipment, i.e. tape and reel, fan-fold box, pick and place trays.
  2. Go to www.4pcb.com/contractassemblers.htm. They have a list of contract assembly houses in North America organized by state/area.

Good luck, Bob Smith

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www.et-info.com/textsuch.htm ET-Info (in German)

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