Design for manufacture
Cost forming factors in PCB production:
1. Quantity and size
of the PCB
2. Number of layers
Try to route your board
with minimum number of layers. Some times is more cost effective to place some
jumpers on the board and to make it single side. Roughly speaking the cost of
double layer = 2 * cost single layer, cost of 4 layers = 2 * cost double layers
3. Effective panelization
The board laminates come in
different sizes, most used size is 1020 mm x 1220 mm (40"x48"). They have to be
cut on panels. Each panel must have technological space around the board area
for registration pins, plating holding frames etc. Each of these operations
generate laminate scrap. Some board sizes utilize up to 80% useability some down
to 50%. This would affect your price.
4. Manufacturing
yeld
Here you can save a lot into the design stage. Don't push the
manufacturer's limits. For instance if your manufacturer can produce 4 mils
don't route all your boards with 4 mils if you have space to route them with 40
mils.
5. Number of holes
The boards are drilled on
sophisticated NC drilling machines. These machines are quite expensive and the
machine time is expensive too, so less holes means less machine time for
drilling and lower cost.
6. Number of hole sizes
The slowest
operation in drilling is the tool change. Usually the boards are drilled at very
high RPM values up to 60-80.000 rpm/min. To change the tool the machine have to
stop the spindle, to wait until the tool stop rotating. To move to the drilling
rack, to place the old tool, to get new tool, to move back to board drill
position, to drive the spindle again and to wait the RPM value to reach the
drill RPM setpoint for the new tool. Each tool change takes approximately the
time for drilling 100-200 holes. Try to minimize the number of drill tools as
much as possible. Combine the tools with difference only few mils if your holes
will pass your required tolerances.
7. Laminate material
When
you intend to manufacture your board in volume the right choice for the board
laminate can save a lot of money. For instance dispite the superior
characteristics of FR-4, all consimer electronics today still is manufactured on
old paper FR-2 laminates.
8. Trace width / space
requirements
This is in close relation with the point 4. For instance if
your traces are wide enough (>20mils) the board can be manufactured with etch
resist single silkscreen priniting operation instead of dry film lamination,
exposure, developing.
9. Special board requirements, controlled
impedances etc.
This affects again the manufacturing yields.
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