Understanding Vertical Probe Cards (1)

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Understanding Vertical Probe Cards

• Semi Probes

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• Vertical-contact probe cards for wafer testing
  have several advantages, including full array
  testing and high parallel probing flexibility.
  Regardless of how the pads are arranged, several
  dice can be probed and examined at the same time.
  Parallel testing procedures can significantly cut
  costs.

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Full -Array Probing

• The widespread use of flip-chips and other array
  bumping techniques necessitates the contact of a
  large number of pads on a single square
  centimeter. Because of the physical limits
  imposed by the needle's horizontal arrangement,
  this application cannot be carried out with epoxy
  ring probe cards.
• Increasing the throughput of a probing line
  lowers test costs and, lowers manufacturing
  costs. As a result, the goal is to test as many
  chips as feasible at the same time while reducing
  the number of touchdowns per wafer. The pads on
  the wafer must be placed in specific patterns for
  epoxy ring probe cards, due to physical
  limitations in the horizontal placement of the
  needles, parallel probing was adopted. Parallel
  probing with epoxy ring probe cards are
  frequently required to be factored into the chip
  design. This highlights a few drawbacks in the
  use of parallel probing.

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High-Temperature Range

• During the die test, the temperature range
  gradually widens. Temperatures of 0 to 125C are
  necessary for numerous sorts of probing
  procedures. In this case, too, the traditional
  probing card technology demonstrates its
  limitations. In terms of thermal behavior, the
  construction of a needle card is exceedingly
  intricate and difficult to control.
• Higher probing requirements can be met with
  vertical-contact probe cards. The buckling-beam
  principle is the foundation for a vertical probe
  card (or buckling wire). The bending or buckling
  of columns is defined by mathematical formulae as
  a function of loads applied to them. This
  relationship demonstrates that if a force is
  applied to the wire's end, the wire will bend and
  generate a spring force that is nearly
  independent of the wire's displacement. The force
  graph is constructed as a function of
  displacement for a buckling wire and a
  compression spring as a comparison. A significant
  non-linear spring characteristic is achieved,
  resulting in homogeneous force distribution over
  all contacts of a vertical probe card, in
  contrast to the spring concept of a needle card.

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Vertical Probing Assembly

• The ViP head, which contacts the wafer (DUT), and
  the ViP connection, which ensures good contact to
  the PCB, make up the vertical probing assembly.
  The ViP head is made up of guide plates that are
  drilled to match the wafer footprint. The holes
  must be placed with exceptional precision to
  ensure high probe positioning accuracy of the
  buckling wires. The ViP head's buckling beams
  align perfectly with the wires in the ViP
  connector, ensuring great contact. This design
  also makes it easy to change the ViP head for
  maintenance. The following capabilities were
  given significant consideration during
  development high density probing flexible,
  parallel probing the high accuracy of contact
  points and suitability for high-temperature
  ranges.

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High-Density Probing

• The vertical technology allows for the precise
  arrangement of thousands of contacts on a postage
  stamp's surface. Buckling beams (spring wires)
  that have been specially made are positioned in
  guide plates that have been perforated according
  to the footprint of the DUT. There are two types
  of vertical probe tip shapes flat and pointy.
  When contacting solder bump vertical probe card,
  a flat tip is always utilized when contacting
  aluminum surfaces, a pointed tip is better since
  it will penetrate any oxide layer and when
  contacting gold surfaces, both pointed and flat
  tips can be used. Parallel probing reduces test
  time by a significant amount. If the contact
  pattern can be easily modified according to the
  intended parallel test strategy, the vertical
  probe card is especially ideal for parallel
  probing. This is accomplished by drilling a guide
  plate based on the DUT's footprints. Parallel
  testing must be factored into the wafer design.

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In Short

• ViProbe can be used to probe memory wafers in a
  variety of ways, including array probing,
  peripheral parallel probing, and multi-die
  probing. When it comes to array probing, the
  ViProbe is particularly well suited to full array
  probing, such as on flip-chip wafers. Semi Probe
  offers a wide range of probe cards and
  accessories, check out for details.

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