Embedded Resistor Laser Trim

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Embedded Resistor Laser Trim

• Dr. D.O.K. (Kim) Fjeldsted
• ESI

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Worldwide Chip-R Forecast
Billions Of Units
SOURCE Prismark Partners LLC Paumonok Group
1/02
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Worldwide Chip-R Forecast By Package Size
SOURCE Paumanok Group Prismark Partners LLC,
1/02
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Embedded Resistor Roadmap
Market Status
Research Development
Prototype
Production
Exploration
Packages Small Modules
Parallel Termination
Markets
Cell Phones
Motherboards
Trim Req
Medium
None
High
Low
Max Value
100 kW
500 W
500 kW
10 untrimmed 1 trimmed
Tolerances
5 trimmed
20 untrimmed
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Worldwide Forecast Cellphones
SOURCE Custer Consulting, 6/02
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Embedded Resistor Technologies Roadmap
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Embedded Resistor Tolerances
SOURCE Greg Lucas 11/01, and others.
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Why Trim?
SOURCE Gould, 5/01
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Achieving Tighter Tolerances

• Without trimming
• Tolerances of 8 16 on embedded resistors
• With laser trimming
• Better than 1 tolerance on trimmed resistors

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Laser Trim In the PWB Process Flow
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Process Related Tolerance Drift
Tolerance
1 5
0
Trim
Subsequent steps (overcoat, lamination, reflow,
etc.)
Print
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The Trimming Process

• The resistor to be trimmed is connected to a
  high-speed test and measurement system
• The laser micromachines a cut in the resistor
  material
• When the resistor reaches its target value, the
  measurement system signals the laser to stop
  cutting

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Before After Laser Trimming
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Change In Resistance With Distance Trimmed
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Double Plunge Trim
1
2
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L-Cut Trim
Target R Value
R in W
Before trim value
Distance of trim
2
1
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Types Of Laser Trims
SERPENTINE
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Probing a Circuit
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Probing a Circuit (contd)
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Probing a Circuit (contd)
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Probing a Circuit (contd)
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Probe and Trim Guidelines

• Board and panel layout
• A systematic regular x-y layout of multi-up
  boards on a panel is preferred
• Pad placement
• A systematic, regular x-y layout of test pads is
  preferred
• Test pads should be arranged in generally
  repeated patterns
• Test pads should be proximal to the resistors
• Probe access (horizontal or vertical) to the test
  pads should not hinder laser view or access
  (overhead, vertical) to any resistors of trim
  interest
• Pad size
• Robust test probes for this application have
  typical tip diameters of 0.006 0.015 (150375
  µm)
• Resistors less than approximately 200 W may
  require 4 point probing (full Kelvin) for 1
  tolerance testing
• Minimum pad size should be 0.025 (625 µm)
  diameter to accommodate typical test probes
• Pad sizes greater than 0.050 (1.25 mm) diameter
  significantly improve test probe placement
  accuracy
• Resistor size
• The laser spot is approximately 0.001 0.007
  (25 175 µm) diameter depending on the subject
  materials
• High accuracy trims (tolerance ? 0.5) are best
  obtained for resistors larger than 0.020 x 0.020
  in2 (500 x 500 µm2)
• Resistors as small as 0.010 x 0.010 in2 (250 x
  250 µm2) are trimmable, with tolerances dependent
  on material and resistance values

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Panel Technologies Roadmap
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Embedded Passive Market
Model 4700 Embedded Passive Laser Trimming System
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Laser Trim on Printed Circuit Board (PCB)
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Embedded Resistor Laser Trim
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Laser Trim on Printed Circuit Board (PCB)
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Metal Thin Film
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Embedded Resistor Laser Trim
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Embedded Resistor Laser Trim
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Process Component Analysis
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Panel of Multiple up Boards

• Step and repeat
• in 6 rows and
• 6 columns
• 110 resistors/board
• 3,960 R/Panel
• (1.41 R/cm2)

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Multiple up Boards and Modules

• 18 resistors/module
• 108 modules/board
• 16 boards/panel
• 31,104 R/Panel
• (11.08 R/cm2)

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Cost of Ownership Model
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Cost Model Sensitivities