| In
the high-mix market served by dsi, the cost of an assembly
is based on the number of labor centers that are required to perform the
assembly and the time spent in each labor center. dsi employs
activity-based costing and has divided the assembly division into over 100
cost centers. |
| With
activity-based costing, there are two facets to consider. The first consideration
is machine, process, or area set-up that includes loading components on
an SMT line or staging through-hole parts on an assembly line. This set-up
cost is usually independent of the number of units to be assembled. Rather,
it is related to the number of different components that must be staged
in the work center. |
| The
second consideration is a variable run-time cost that changes based on the
total quantity of components to be processed within the work center. For
example, it might take one hour to set up an SMT machine, but the run time
(placing the components) might be only a few minutes. The cost of the job
within the work center is the sum of the set-up time and the process time,
all multiplied by the cost per minute for the work center. Because the work
center cost includes the set-up cost, the unit cost of the assembly becomes
highly dependent on the lot size processed through the work center. |
The
following characteristics can affect the cost of your circuit board assembly.
|
Assemblies
Requiring Surface Mount Components Only
- Fine pitch
components (with pitches 16 mil and under)
- High numbers
of QFP / BGA packages (waffle trays)
- 0201 packages
- Components
not supplied on tape & reel with allowance for feeder leader
or in tubes
- SMT components
requiring hand placement (ones larger than 2" or that snap
into place)
- Moisture
sensitive components (particularly ones with MSD levels of 5a
& 6)
- Edge connectors
which must be soldered top and bottom side
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|
Assemblies
Requiring Surface Mount & Through-hole Components (Mixed Technology)
Same items listed above as well as:
- SMT packages
smaller than 0603 on the solder side (if wave soldering)
- SMT components
placed on the wave side that cannot be wave soldered
(QFP / TSSOP / BGA / TO220 / SOIC less than 50 mil)
- Large numbers
of through-hole components on the solder side of the board
- Through-hole
components that hang off the edge of the board
|
|
Assemblies
Requiring Through-hole Components Only
- Components
requiring hand soldering including parts soldered to large ground
planes
- Complicated
hardware and heat sink
|
|
Other
Considerations
- Builds requiring
special handling (IPC Class 3 Builds)
- In-circuit
testing or functional testing with limited test points and/or
test coverage
- Bills of
material that do not contain secondary suppliers or cross-referenced
parts
- Special materials
(conformal coating, potting, bonding, etc.)
- Bills of
material that contain a high number of single-use components.
This increases the set-up cost, but has little impact on the run-time
cost.
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