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Browse Prior Art Database

Flex Circuit to Replace External Wires

IP.com Disclosure Number: IPCOM000111750D
Original Publication Date: 1994-Mar-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 91K

Publishing Venue

IBM

Related People

Kornfeld, J: AUTHOR [+2]

Abstract

During the development of a new product, circuit cards are changed many times prior to the final design. When minior changes are made to a current embedded level of a card, external wires are often added for new circuits and land cuts are made to delete circuits. This process allows changes to be made very fast to exiting cards. After a pre-defined number of external-wire changes are made, a new embed raw card is released. The process starts over with the next change.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Flex Circuit to Replace External Wires

      During the development of a new product, circuit cards are
changed many times prior to the final design.  When minior changes
are made to a current embedded level of a card, external wires are
often added for new circuits and land cuts are made to delete
circuits.  This process allows changes to be made very fast to
exiting cards.  After a pre-defined number of external-wire changes
are made, a new embed raw card is released.  The process starts over
with the next change.

      Several problems have been found using the external-wire method
to make changes.  These problems can be resolved by using a flex
ciruit instead of external wires.

      PROBLEM 1 - When external wires are added to the back of the
card, they are loose except on each end.  When the card is handled or
inserted into the card cage, the wires can snag on other components
and can be broken or pulled off at the solder joint.  If not noticed,
this causes machine failure and re-work to repair the machine is
necessary.  This problem is enlarged after many external wires are
added as they cross over one another and protrude from the back of
the card.  This situation has caused card manufacturers to force an
early embed when only a few external wires have been added.

      PROBLEM 2 - In high frequency circuits, the length of the
embedded trace is very important to the proper operation of the
circuit.  Because of the difficulty of controlling the length and
routing of external wires, some circuits do not operate the same.

      PROBLEM 3 - With the external wires routed across the back of
the card, they can act as antennas and radiate electrical noise to
other cards or receive noise from other cards.  This can cause the
circuit of this card or another card to not perform as desired.

      The proposed new process would solve all three of the
aforementioned problems.  It involves making a flex ciruit
incorporating the desired changes and soldering it to the back of the
card to be reworked.  The process to delete wire/circuit changes
remains unchanged.

      When the added cicuitry is determined, a layout, including the
proper circuit design, routing can be designed.  From this layout a
flex circuit can be produced that will incorporate the desired
changes.  At each lead termination point, a thru hole will be made to
permit attachment to the solder point on the card.

      The f...