On Friday 07 March 2008 07:27:31 pm Richard Cooke wrote:
> Is there a rule of thumb for estimating the cost of getting circuit
> boards assembled?
In a past life I worked for a large Contract Manufacture,
http://www.matrc.com . I don't mean this to a plug for them,
but the tour of the place is helpful for the discusion:
http://www.matric.com/tour.html
http://www.matric.com/info/tour/smt.htm
To a CM it is all about *Time*. When it comes to parts, the actually part
cost is really insignificant as far as cost contribution goes. Most of the
cost goes to the time it takes to setup and teardown.
For a broad brush overview of cost steps:
One shot fee for getting your project into the system. Someone
has to enter your BOM, and schedule into the amourphys blob
known as "The System". Any change that you do triggers
a recalculation, that you either payfor or is amortized
across your boards. Every future order you place will have
a small "trigger few" to pay for someone to enter your order.
Included in that is a fee for someone to do a time analyze of the number of
operations that your project will require. A unit time value is assigned to
each operation, and each operation has a cost, that is, as far
as I know, calculated by Magick (All CM's use Magick for this step
to my knowledge).
If you supply the parts there will be fees for entering a carrying
fee per new part number into The System. Some cost analysis guru at GM,
long ago, decided to simply have a number in The System carries
a charge of $50 or so per year. The accountants just love
to beat up the engineering department for "we have to many
parts in the warehouse". Company owner wants to keep
inventory turnover high. Also cost for physically getting
your parts into The System, such has putting them
in the warehouse, typing in the data etc.
There will be a scrapping fee to get your stuff
out of The System if you take your project someplace
else.
Those None Recurring Engineering (NRE) fees you either
pay for up front, or it is amortized across the number of boards.
This is why the range can seem so different between different
CMs. Some hide the fees, some don't.
Also when you supply the parts the price of each part
will be market up by a *minimum* of 33% (More Guru
calculations). If you don't mark the price up by
this amount you lose money each time you touch the part.
You are changed for the use of the warehouse space,
like renting a storage unit.
Now lets say you let the CM supply the parts. In general
this will get you a lower per part cost for the commodity parts.
As they will be using 100,000 0.1 uF 0603 caps a day,
the pick and place machine will have that loaded.
So you don't have to pay for loading your reel of
much smaller volume part. Also the CM will have
negotiated a much better price than you got
from Digikey. The downside here is that you lose
some measure of control, which can be a problem
if you have to meet UL/MSHA/FDA etc. regulations.
Which reminds me there will be extera charges
for projects that involve the pain of FDA paperwork,
such a per lot tracking etc. Other acronyms
apply as well, UL, FCC etc.
There is a fee for having the solder paste stencil made.
Now that the NRE's are out of the way, lets build
a Thousand Widgets.
Someone answers the phone and enters
an order into The System to build a Thousand Widgets.
The System checks the warehouse to see if all
of the parts area available. Your order
is then routed to Purchasing to get the parts
that are not available ordered, or routed
to planing to get your order into the build
que.
When your build hits the top of the que:
Someone pulls the parts from the warehouse,
at the minimum your PCB; time.
Your bareboards are put in an oven and baked to drive out any moisture,
you pay the handling and electricity; time.
Your parts are loaded on the Pick&Place machine; time.
The board go from the oven to SMT Assembly; time.
Someone pulls your stencil out of the rack and puts it in the paste machine.
Past is applied to your board; time.
Your board is put into the Pick&Place and your parts are mounted; electricity
and time.
Your board then goes through the IR reflow oven for soldering; electricity and
time.
The boards are then cleaned; fluids and time.
Any of your parts left on the P&P are removed, and put
back in the warehouse, when Widget #1000 comes out
the end of the machine; time.
The stencil is cleaned. You pay for whatever the cleaning
fluid is and time.
The stencil is put back in the rack; time.
If your boards are in a array, they are then cut apart.
It is cheaper to build arrays, but it adds this cutting fee; time.
If there are parts that could not be mounted in the P&P machine
they are done by hand, or put through the wave solder machine,
then cleaned a second time. There is a big hit in costs for
anyting done by hand such as connectors, transformers,
cable assemblies etc. Time.
The boards then go to Quality Control for the level of inspection
that you paid for. Simple visual to full functional test. Time
Boards leave QC and go to shipping where they are put
in Anti-Static bags and cardboard boxes and shipped off
to you. Time.
You pay the shipping one way or the other.
There could also be Added Value items such as your boards
are put in an enclosure. You pay for someone to do it right
down to the number of seconds it takes to tighten down the
screws.
By now you probably have gotten the idea that Time is important.
When you were looking up stuff in the DigiKey catalog were you
billing yourself the time it took to do it? Probably not...
> The 500 piece cost for the electonic parts from Digi-key is
> about $4.20
Did you include the Anti-Static Bag, the yellow Anti-Static
Sticker that seals the bag, the solder (price of metals is going up every
day), and any board cleaning fluid chemicals / deionized-water in that price
of $4.20, and the time to do those items? I didn't think so...
A good CM knows the cost of every operation and will be around a long time.
A new CM doesn't know his costs. Hence the wide variation in CM quotes.
Matric developed a reputation for being a high price CM, and customers
would leave based on cost, rather than value. However many of them would
return after a while saying "we got what we paid for", and never left again.
In the end my advice is to analyze the value of the services you are paying
for, not the cost of the parts.
--
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