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Re: Approximate cost of pcb assembly

N

Nemo

Jan 1, 1970
0
What is the approximate cost of pcb assembly relative to pcb
fabrication for low quantities? If I have 50 boards ordered at about
30\$ each for pcb fab can I expect about a 1:1 cost for assembly?

Lots of variables, but for a first finger-in-the-air estimate that's not
going to be far off.

In general for LARGE runs the assemblers consider how many components
there are to place, of how many different types. This determines how
much time / how many different types of reel will be needed.

But for small runs other items dominate the cost. Apart from component
prices, you need to consider if the components are available in these
quantities (that's tripped me up recently - I spec'd something only
available in quantities of 250 or more); how many different suppliers
the assembler will need to deal with, because that will take a lot of
time; whether there are any special operations like, mounting components
on the underside of a board.

I recently used a tiny (1 man!) assembler in the UK who used a
semi-automatic SM assembly machine. It was very impressive, placing
things under manual control but doing the fiddly work for him. Good
blend of machine and man for small scale stuff. Many assembly houses are
either purely manual or purely large-scale automatic SM machines, with
all the setup hassle their overheads imply.

J

John Larkin

Jan 1, 1970
0
Lots of variables, but for a first finger-in-the-air estimate that's not
going to be far off.

In general for LARGE runs the assemblers consider how many components
there are to place, of how many different types. This determines how
much time / how many different types of reel will be needed.

But for small runs other items dominate the cost. Apart from component
prices, you need to consider if the components are available in these
quantities (that's tripped me up recently - I spec'd something only
available in quantities of 250 or more); how many different suppliers
the assembler will need to deal with, because that will take a lot of
time; whether there are any special operations like, mounting components
on the underside of a board.

I recently used a tiny (1 man!) assembler in the UK who used a
semi-automatic SM assembly machine. It was very impressive, placing
things under manual control but doing the fiddly work for him. Good
blend of machine and man for small scale stuff. Many assembly houses are
either purely manual or purely large-scale automatic SM machines, with
all the setup hassle their overheads imply.

We have a couple of Essemtec semi-auto p+p machines. Great stuff.

John

N

Nemo

Jan 1, 1970
0
Bobby Joe writes
How does one setup the board to handle it? Do I need special placement
and alignment markings or is everything pretty much handled by the
EDA? Does the board need to have a boarder with the markings so I have
to add that or can I get away with just placing some markings in the
most convenient location and the placement machine will handle it?

I guess what I really need is an online site that explains the
process. I suppose I have to buy the components in reels and ship them
to them too? Do I get the left overs back? I suppose I can also do
partial assembly? Such as just the passives and I can handle solder
the IC's if need be?

For a relatively small run like this there are no industry standard
rules. You need to talk it over with the assembler you choose and they
will guide you through their assembly procedure. The small / medium ones
are pretty flexible as *they want your business*. Your CAD package can
probably output an x,y file to aid machine assembly of PCB's - ie "R4 is
at origin + 23mm in the x direction, +12mm in y direction". I think most
people put their origin at the bottom left corner of the PCB but it's
arbitrary. Some assemblers like "fiducial" marks (target shaped things)
on the PCB's to centre their camera-based component placement machines.

If you ask for the leftover components back, you should get them.

If mounting tiny LED's make sure there is some obvious polarisation.
I've seen PCB's where not one LED lit up because they'd all been put in
the wrong way round. Machine assembly is nothing if not consistent!
These days if I choose an LED I make sure there's some way to tell if
it's the right way round - not always an option if your design requires
miniaturisation, in which case you need to look at the manufacturer's
specs to see which way round it is fitted in the reel.

Anyhow - basically choose an assembler or two, then discuss with their
production engineers over the best approach.

If you're in the UK I can maybe help you a bit further with finding a
suitable assembler. If you're in the States, I leave you to the tender
mercies of your countrymen. Sounds like you're in a good position
though, a small run like this implies you are in a small company thus
have freedom to do whatever suits you - unlike large companies where you
have to use the Approved Suppliers and Procedures 8)

B

Ben Jackson

Jan 1, 1970
0
Your CAD package can
probably output an x,y file to aid machine assembly of PCB's - ie "R4 is
at origin + 23mm in the x direction, +12mm in y direction". I think most
people put their origin at the bottom left corner of the PCB but it's
arbitrary. Some assemblers like "fiducial" marks (target shaped things)
on the PCB's to centre their camera-based component placement machines.

My understanding from discussion of XY files on the PCB dev list is
that the exact XY position (center of the part, corner of the part,
etc) is so machine/vendor specific that they only expect rough
figures anyway. Then as part of the setup they tweak that file to
their process.

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