PPS Pro version 8.2 - 第174页
User Manual 4022 591 98247 170 PPS-Pro v8.2 05.07 Guidelines for using PPS-Pro componen ts that the s ystem w ould search f or in the G erber file . How ever , standar d pad lay out design s often chan ge and man y desig…
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APPENDIX B Gerber Files
B.1 What is Gerber Data?
Many people have difficulty evaluating and using Gerber processing software
because it is difficult to see how it relates to “CAD data”.
Gerber data is an old data format (in the electronics assembly calendar) that is
used to operate photo plotters. Photo plotters create the patterns of bare
boards and therefore the data used to drive the plotter is the closest represen
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tation of the actual product available. Conversely, people not involved in
assembly develop CAD data during board design. The X, Y positions of
components are defined by part libraries in the CAD system that may not match
the centroid that the manufacturing engineer needs for the placement or
insertion system. This CAD data is then used to generate the Gerber files in an
additional step. There are often differences between ASCII CAD positional data
and Gerber data due to the CAD system’s design as well as the conversion
process to Gerber.
Furthermore, if the board fabricator makes changes to the Gerber file for manu-
facturability reasons, the CAD data is then useless. Gerber data is also generally
available since it must be used to fabricate the board, and the data is stand
-
ardized unlike the myriad of different CAD formats on the market. For a manu-
facturer receiving boards from many different customers with different CAD
systems, the cost of several interfaces and the training involved in different
formats can be prohibitively expensive. Don’t worry about software revision.
changes to data formats— Gerber data is a universally employed format and is
here to stay! In general, it is the most accurate, most available, and only truly
standardized board data!
B.2 The Downside of Gerber Data
Because the Gerber format is so old, the previous version
(274D)
is plagued by
a need for what is called an
“aperture list.”
To understand aperture lists,
consider a pen plotter, which is very similar to the older photo plotting
equipment. The pen needs to be moved about the paper and the plotter must be
told which pen to use at all times. Original photo plotters used light shined
through “apertures” to project the board patterns. The aperture list is a file
separate from the Gerber files and defines the apertures used by the CAD
engineer’s system when the file was generated. This sounds simple enough—
except that there is no standard for aperture list formatting and they are often
difficult to import for use by a Gerber digitizing system.
The Gerber format
(274X)
eliminates the need for aperture lists and is
becoming more common. Gerber data consists only of graphics. There is no data
storage of part information, rotation, or designator. Also, until recently there
was no way to easily extract the pad or through-hole groupings of each
component due to the graphics-only nature of the data. Systems required that
the user maintain and develop “libraries” of standard pad groupings of
User Manual 4022 591 98247
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Guidelines for using PPS-Pro
components that the system would search for in the Gerber file. However,
standard pad layout designs often change and many designers customize their
pad groupings for various reasons, rendering these libraries useless. The
operator then needs to “teach” the new groupings. As you can imagine, this
becomes a time intensive and aggravating task for the operator of the appli
-
cation. Finally, until recently, the fastest means of extracting reference desig-
nators from the file was a text recognition system that looks for text of a
certain size and then joins it to the closest part on the board. This process
takes a very long time and is not always reliable. As anyone who works with
boards knows, the reference designators are often difficult to associate with
component locations on dense assemblies— imagine how hard it is for a
computer lacking intuition! Also imagine how hard it is to find the errors the
computer made on a 400-component board! You might as well enter the data
manually in the first place. Finally, present digitizers cannot process layers
with traces on them and need special, time-consuming manipulation of rastered
pads.
(See definition below)
B.3 What is a rastered pad?
Pads are often drawn as a single “flash” in Gerber files. However, as technology
changes, more files are using “rastered pads.” Each pad can be constructed of
many lines (40-60) drawn in a zigzag fashion to fill in the pad area. In order for
most Gerber digitizers to accept this type of pad, extra manual manipulation is
needed on each component to change the pads into flashes! This is a time-
consuming step on your way to a digitized assembly.
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APPENDIX C What to do in case of a problem
C.1 Survey
To enable Assembléon to find a solution data must be gathered, some checks
can be performed that may lead to a solution right away. These checks are
described in the ‘pre-gather-stage’. If eventually no solution is found, all
information must be gathered. This is described in the ‘gather-stage’. After
this stage, all information can be sent to the local Customer Support
(hereafter CS). This is described in the ‘post-gather-stage’. All three stages are
related to PPS 8.1.
If you are familiar with gathering information, the checklist can directly be
used
(see C.4 on page 178).
C.2 Pre gather stage
Before submitting the information, you can try to find the solution by
yourself. This chapter provides you with some checks which can be performed
in order to attempt this:
■ Check the Release Notes if it is documented and known
■ Use the manual, maybe the solution is already described.
■ Ensure that the latest software version has been installed.
■ Place the project on a local drive if it is not already placed.
■ Check if the length of the total path does not exceed the maximum path-
length which is described in the user manual.
■ Delete all spaces in path and file names.
■ Delete all forbidden characters which are described in the user manual.
■ Use the correct ALE file.
■ Use the correct PSI file.
■ Use the correct aperture files
■ Check that there is enough free diskspace available (20Mb).
■ Check the read/write rights on the involved files and/or directories.
■ Use Help (see SCREEN 86 on page 172).