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Method of Designing a Double-Sided PCB Requiring Only One Solder Stencil Image

IP.com Disclosure Number: IPCOM000116931D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 119K

Publishing Venue

IBM

Related People

Csonka-Peeren, JV: AUTHOR [+2]

Abstract

Disclosed is a method of obtaining an identical footprint pattern for a double-sided PCB, which requires only one stencil image for solder paste application. The method involves the creation and placement of "dummy" pads on the PCB surfaces, namely pads which do not serve a functional purpose and are not connected to any part of the PCB electrical circuit.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Method of Designing a Double-Sided PCB Requiring Only One Solder
Stencil Image

      Disclosed is a method of obtaining an identical footprint
pattern for a double-sided PCB, which requires only one stencil image
for solder paste application.  The method involves the creation and
placement of "dummy" pads on the PCB surfaces, namely pads which do
not serve a functional purpose and are not connected to any part of
the PCB electrical circuit.

      During PCB assembly, a pad footprint image on the foil of a
stencil is used to apply solder paste to a panel of a PCB.  Solder
paste is pressed through all of the apertures of the image onto the
surface of the panel, thereby forming a pattern of pads onto which
electronic components are placed in later stages of assembly.  For
double-sided asymmetrical panels two different images are required,
one for the first surface of the panel and the other for the second
surface thereof.  However, a symmetrical panel, requiring a single
panel image to apply paste to the front and back sides, can be
obtained if the front and back sides of the double-sided PCB are
designed to have an identical footprint pattern.

      Figs. 1A and 1B show a PCB which has an identical footprint
pattern on the front (Fig. 1A) and back (Fig. 1B) surfaces.  These
figures show the pads, wiring, and vias on each surface, and the card
outline with the edges labelled.  The method for generating an
identical footprint pattern for the front and back sides of a PCB is
practised as follows:
  1.  A pair of reference points is first defined for the PCB, each
       reference point pertaining to one surface of the PCB.  The
       geometric relationship between the chosen reference points
must
       be such that they are located along the same edge of the PCB,
at
       opposite corners thereof.  For instance, if the edges of the
       first surface of the PCB are labelled in a clockwise direction
in
       Fig. 1A as A, B, C and D, respectively, the point where the
       extensions of edges A and D meet may be selected to define the
       reference point or origin of the first panel surface.
Rotation
       of the panel surface of Fig. 1A by 180 degrees about edge A
will
       reveal the second panel surface, as shown in Fig. 1B.  The
point
       where edges C and D of the second surface meet may be selected
to
       define the origin for the second panel surface.  As explained,
       each of these selected point...