Si Chip Electrical Contact

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Si Chip Electrical Contact

• Wire bonding
• Tape Automated Bonding (TAB)
• Flip chip
• Planar bonding

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Wire Bonding

• Ultrasonic
• Thermo-compression
• Thermosonic
• Geometry Types
• Ball - wedgeShown in illustration
• Wedge - wedge

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Wire Bonding
From Small Precision Tools
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(No Transcript)
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Tape Automated Bonding (TAB)

• Fig. 3.26 A picture of a TAB film with the Cu
  pattern, as well as the holes in the film for
  excising the circuits, and the sprocket holes for
  moving the film during processing.

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Tape Automated Bonding (TAB)

• Interconnection by metallized flexible polymer
  tape

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Tape Automated Bonding (TAB)

• Connection made in two steps
• Inner Lead Bonding
• Connecting tape to chip
• Outer Lead Bonding
• Connecting tape to substrate
• Connection made by thermocompression

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TAB, continued

• Standard process
• Fabrication of gold bumps (Fig. 3.28)
• Deposition of contact/barrier metals
• Photolithography
• Electroplating
• Strip and etch barrier metals

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TAB, continued

• Fig. 3.27 The main steps in TAB processing.

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Advantages of TAB

• High packaging density
• Can contact chips with gt1000 I/O
• Excellent electrical properties (high frequency)
• Robust mounting
• Pre-testable (contrary to COB)
• Gold bumps give hermetic seal to chip
• Gang bonding gives high yield, is less time
  consuming than wirebonding
• TAB film can be used as daughter board

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Disadvantages of TAB

• Non-standard wafer processes
• Special custom design film for chip
• Needs special machine/tool for OLB
• Demanding repair
• Low availability of std. chips and TAB service
• Little standardization

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Flip chip

• Active face of chip is flipped towards substrate
• Substrate pads are identical to chip pads
• Area array connections possible
• All connections done simultaneously
• Smallest possible footprint (11)
• Short interconnections
• Low inductance and resistance
• Excellent electrical properties
• Little flexibility
• Change of chip pad configuration implies redesign
  of substrate
• Small, but increasing amount of interconnections
  are flip chip
• To be dealt with in much more detail

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Flip Chip, history

• Introduced by IBM 1962
• Flip chip has been used for decades, but with
  little impact
• Wire bonding is far more common
• Flip chip technology has not been considered
  mature
• The industrial infrastructure has been small
• The market share of flip chip connections is
  believed to increase significantly
• Wire bonding will remain dominating for many
  years
• Flip chip especially for advanced packaging

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Flip Chip consists of

• Chip
• Si, GaAs, etc.
• Substrate
• Ceramic, organic, dielectic-covered metal,
  silicon, etc.
• Interconnection system
• Metallization on chip and substrate pads
• Chip (or substrate) bumps
• Bonding material
• Underfill encapsulant

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Different Flip Chip technologies

• Flip chip is not standardized!

From C. Lee, ESTC 2006, Dresden
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Flip Chip, continued

• Advantages
• Highest packing density
• Excellent hi freq. properties
• Up to 10 000 I/O
• Disadvantages
• Very difficult placement and reliable
  solder/cleaning
• Lack of thermal flexibility

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Planar Bonding with Adaptive Routing

• Fig. 3.32 Planar bonding with laser-assisted
  adaptive conductor routing. The top two figures
  a) and b) show a substrate cross section with
  details of the mounting of the chip in an etched
  through-hole. Figure c) shows the conductor
  layers and polyimide insulation on top of the
  substrate. The bottom figures show an exploded
  view of all the layers.

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End of Chapter 3 Materials and Basic Processes

• Important issues
• Materials
• Distinguish between metals, ceramics, glasses and
  plastics
• Important mechanical and thermal parameters like
  modulus of eleasticity, thermal expansion
  coefficient and thermal conductivity.
• Important electrical parameters like dielectric
  constant and resistivity or conductivity
• Have a basic understand of the importance and
  value of the most important materials parameter,
  and why they are important for the use of the
  specific material in specific applications.
• For instance knowing the electrical conductivity
  of copper or thermal conductivity of epoxy within
  an accuracy of 25
• Basic processes
• Lithographics, screen and stencil printing,
  etching, plating, vacuum deposition, sputtering,
  soldering, gluing, wire bonding, TAB, and flip
  chip
• Other basic processes described in other
  chapters, like surface mount technology
• Questions and discussions?