Work With PNC To Reduce PC Board Costs

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Work With PNC To Reduce PC Board Costs
When it comes to reducing the manufacturing cost
of a PCB, it is important to remember that a
significant part of the cost of a PCB assembly is
already baked in at the design concept stage. 
The product concept defines the PCB size and
shape, while the performance of the system
dictates the microprocessor, memory and other
functional elements of the circuit.
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However, some of the assembly cost can still be
affected by design choices made by the PCB
designer.  A PCB that is designed for
manufacturing (DFM) can reduce both the
fabrication cost of the PCB and the costs of
component assembly and soldering. A DFM approach
to design can also reduce the likelihood of the
hidden costs of poor yield in production.
The best way to achieve the lowest cost, most
manufacturable design is to work closely with the
prospective  manufacturer, since the way to
maximize DFM cost savings is to design for a
manufacturers specific equipment and technology,
rather than to rely on general rules.
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Reducing PCB Fabrication Costs
The first step to reducing costs in PCB
fabrication to reduce the number of operations
performed by the manufacturer.  The second step
is to optimize the PCB design to leverage a
manufacturers particular fabrication technology.
One way to reduce costs is to eliminate or
minimize the amount of machining required around
the board edge or within the PCB itself. 
Rectilinear PCB outlines without internal slots
will minimize machining, and the rectangular
shape allows the PCB to be grouped in larger
panels that are separated after assembly.  These
large panels streamline assembly by allowing a
several PCB to go through component assembly and
reflow at the same time, improving throughput.
For example, PNC can process a maximum panel size
of 18 X 24. To ensure that the components on
the PCB are not damaged during the scoring and
separation from the panel, components should be
kept 200 mil from the board edge.
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Reducing board layers to reduce fabrication costs
The generally accepted rule that reducing the
number of PCB layers in a stack-up will reduce
cost has become more complicated with the advent
of HDI technology.   The reason is that the cost
of an additional Printed Circuit Board layer is
not linear, so a cost calculation needs to be
made for each jump in the number of layers.
Is it cheaper to use finer trace widths and
buried vias to reduce the layer count from six to
four?  Only the manufacturer is going to know. 
However, as a board gets past eight layers costs
increase non-linearly with each additional
layer.  The aspect ratio of the through hole vias
begin to become a factor, as well as the sheer
number of vias that need to be drilled and plated
to connect all those layers.   At an eight layer
stack up or above, the additional cost of HDI
technology begins to make economic sense if it is
used to reduce the number of stack-up layers
required.
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Respect drill to copper clearance and aspect
ratio design rules
Respect the design rules for hole sizes and hole
to copper clearance.  If the real estate on the
PCB allows it, selecting hole sizes clearances
and annular ring sizes larger than the absolute
minimum will improve fabrication yield. Here are
the through hole design rules for PNC
Non-Plated Through Hole (NPTH)? Finished hole
size (minimum) 0.006"? Edge to edge clearance
(from any other surface element) (minimum)
0.005"Plated Through Hole (PTH)? Finished hole
size (Minimum) 0.004"? Annular ring size
(Minimum) 0.004? Edge to edge clearance (from
any other surface element) (minimum) 0.009"
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Reducing PCB Assembly Costs
To reduce assembly costs the objective is the
same as reducing PCB fabrication costs reduce
the number of operations, and optimize the PCB
design to leverage a manufacturers particular
fabrication technology.
One easy way to reduce assembly costs is to stay
away from the smallest passive packages.  0603
passives are easier to place than 0402 or the
almost invisible 0201.  If possible, chose active
parts that have leads rather than ball grids,
because they are easier to place, they can be
visually inspected instead of x-rayed, and they
are easier to rework.
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Avoid parts that have to be manually soldered
Manual operations are always expensive, and the
designer should do everything they can to avoid
the need for them.
Component manufacturers have recognized this and
now offer through-hole components (typically
connectors) that can be reflow soldered.  This
technology called Through-Hole Reflow allows
through-hole components to be soldered in the
same reflow process as the SMD components,
eliminating a pass through the wave soldering
machine or manual soldering.
Finally, if possible, avoid putting components on
both sides of the board.  The cost of a higher
density PCB with components on one side may be
cheaper than a lower density PCB with components
on both sides.
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Dont wait until the PCB design is finished
before talking with PNC
The best time to talk with the PC Board design
experts at PNC is early in the layout process. 
They can tell you when to use HDI to reduce costs
and can advise on how to optimize panel size. The
experts in the assembly department can also work
with you to select components that will reduce
assembly costs and increase yield.
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Contact Us
115 East Centre St. Nutley, NJ 07110
PHONE [phone]
EMAIL sales_at_pnconline.com
www.pnconline.com