Many schematics will incorporate new parts and these
present the greatest challenge to design processing.
New parts require that a job “Place Holder” be created
that can be used to collect decal, package, description
and a full company part number. Index Designs
designed its parallel BOM such that components
without part numbers are maintained and design
information can be collected through the process. The
state of each BOM line item is identified using color.
The logic by which BOM items are color-coded depends
on the view selected by the user. Having the data to
drive a PCB design process does not imply the data
exists to drive the assembly process. Jobs from
external customers might be annotated to where they
can be assembled but not to the degree required to
drive PCB assembly.
7. Additional Functions
Probably the most unique and useful piece of code in
the Index Designs library is a custom electronic
component indexing and lookup engine. This engine
uses several techniques to reduce a BOM line item
description to an in house part number. A very common
task is to convert microfarads to Pico farads. Line items
such a 0.001uf are matched to 1000pf. The indexer is
driven from any data source that contains a Company
Part number and a description. Additional code was
required to synchronize indexer tables with a company
database in a time efficient manner.
The second major requirement was a tool that allows a
complete machine setup to be saved, recalled and
changed. During the course of preparing a job for
assembly it is common to get “Changes”. Either an
existing part must change or a new part must be added.
In either case existing trays might already be stuffed
and the new or changed component must be worked
into the job setup.
The third major function that Index Designs has recently
added is a Package Wizard. The current scheme
required two PowerPCB libraries, one for land patterns
and another that identifies package shapes and contact
areas. A Package Wizard has been added that allows
parts definitions to be constructed outside of the
PowerPCB library editor. These package definitions are
applied against a IPC-7351 rule sets and generates
PowerPCB land patterns. This new scheme reduces the
number of libraries and allows quick and accurate
generation of land patterns.
8. Summary
While Index Designs has developed a significant
amount of code to automate this process (42K lines in
Delphi at last count) much of this has been added to
expedite the assembly of external jobs. If only in house
schematics and PCB designs are to be assembled then
several processes can be simplified.
• Only rotational data is required to map from
PowerPCB rotation to machine rotation. A very
simple script can adjust the CAM outputs.
• No search engine is required if schematic
library attributes are used to store rotation and
part feeder information. The search engine is a
powerful technique but most engineering
groups already live with extensive library
attributes.
• Trays are very useful for feeding all types of
loose parts but the code to “Compile” a BOM
into tray configurations is very complex. Strips
of tape placed on pin trays might be able to
simplify assembly machine setup. Much of what
is possible depends on assembly machine
software.
The current scheme at Index Designs has reduced part
setup to 1 hour for two medium sized boards with
remaining machine setup at about 30 minutes. Much of
this setup is preformed “Off Line” from the assembly
machine and does not affect other jobs. Stencil setup
and tear down requires another 30 minutes. Hand
placing of these boards is 4 to 6 hours each.
The remaining area where costs can be reduced is in
stencil costs. Stencil costs are currently about $150 per
side and there are shipping costs and delays. Our plan is to laser cut stencils using data from the new Package
Wizard.
Quality assembly starts with getting the correct amount
of solder paste in the correct position. Lead contact
areas define the correct position of paste. Solder paste
files that are received from customers tend to be based
on land patterns and for from optimal. If Index Designs
can generate custom laser cut stencils from package
data it should be able to improve the quality of the
assembled product and reduce costs.
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