Download - Test Trimming - Jerry Gao
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Jerry Gao2014-9-13
Test Trimming
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Why TrimmingTrimming allows the quality of a product to be enhanced during testing.
This is the only aspect of testing that adds value to the device.
Trimming is frequently performed after packaging to compensate for packaging effects.
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Simple Trimming Circuit
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Trimming Type
Fuse ( poly, metal )Laser ZenerE/EEPROM
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Trimming Type
Fuse
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FusePoly Fuse
Metal Fuse
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Rlsb
2Rlsb
4Rlsb
Rx
F1
F2
F3
RxRlsb/4
F3
Rlsb/2
F2
Rlsb
F1
Series-Connected Trim Memory/Ref.
Parallel-Connected Trim Memory/Ref.
Binary Weighted Resistor Trim Schemes Using Fuses
Fuses are blown by forcing a controlled current through them.A blown fuse appears to be an open circuit.Probe pads and control pads for each fuse are required.
No simulation available (difficult to simulate an open circuit).
TrimMemory
TrimReference
TrimReference
TrimMemory
Probe Pad
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Poly Fuse Specification
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Poly Fuse Blown Waveform
• Approximate 500ns duration of currents pulse during fuse blowing• Current pulse provide
For 3 fuses, take one capacitor 47uF
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Fuse Layout Before and After Trimming
Layout Of View Of Fuse MemoryBefore Trim
Microphotograph Of View Of Fuse MemoryAfter Trim
(Fuse links blown by laser)
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Trimming Type
FuseLaser
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Silicon-Oxide
p substrate
Thin-FilmDeposits
Example Laser Trims
Laser cut
Laser cut
Laser Trimming Thin-Film Resistors
Cut a thin-film resistor with a laser to increase its resistance value.Performed at the wafer level.
Rlsb
2Rlsb
4Rlsb
Rx
Trim Memory/Ref.
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Laser Trimming Metal Fuse
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Trimming Type
FuseLaserZener
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Series-ConnectedTrim Memory/Ref.
Rlsb
2Rlsb
4Rlsb
Rx
Z1
Z2
Z3
RxRlsb/4
Z3
Rlsb/2
Z2
Rlsb
Z1
Parallel-Connected Trim Memory/Ref.
Binary Weighted Resistor Trim Schemes Using Zener Diodes
Zener diodes are blown by forcing a controlled current through them.
A blown zener diode appears to be a short circuit.Probe pads and control pads are required for each zener diode.
Can be simulated to verify best trim code.
Probe Pad
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Trim Simulation Using Zener Diodes
Zener trim technology provides the ability to simulate zap effects by temporarily shorting individual zener diodes with test hardware relays.
There are no simulation techniques available for Fuse technology.
E/EEPROM technology can be simulated.
Trim Memory Trimmable
ReferenceControlRegisters Simulation Mode Trim Value
Simulation Mode Control
ReferenceVoltage
MUX
Trim Code
Rlsb
2Rlsb
4Rlsb
Rx
Z1
Z2
Z3
Switc
h D
ecod
er
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Zapping Zeners
Typical I/V Requirements:ABCD150 - ~13 V, 300 mAPVIP50 - ~5 V, 20 mA
Voltage in yellow, Current in red.
Voltage rises until zener breakdown
Current probe had offset, absolute values are shifted (notice negative current before the zap)
At breakdown, current increases quickly
Zener breakdown ~11v in this case
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After Zener Zap
Good zener zapBad zener zap, excessive current
A clear bright silver line in
junction indicates good
zap.
In some cases, the flow is
subterranean, and appears as a
fuzzy line.
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Trimming Type
FuseLaserZenerE/EEPROM
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E/EEPROM Trimmable Reference Circuit
E/EEPROM registers store digital values in memory that allow a DAC to adjust current or voltage values.
Except for the control pads, no probe pads are required.
EPROMS (One-Time Electrical Programmable Read Only Memory) can be programmed but not erased.
They can be programmed one time only, so these are used after the code is bug free.
An EEPROM (Electrically Erasable Programmable Read Only Memory) is similar to an EPROM but it can be erased.
Can be programmed many times, hence trim errors can be easily corrected.
E/EEPROM DAC
Trim Memory
E/EEPROM
Floating Gate MOS Technology
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EPROM Programming
Simulate and find the best-fit trim code.Program the EPROM register and verify result.Cycle power and read back programmed data. Verify that it is the correct data.Verify all electrical parameters.
EPROMRegisterControl
Registers
Test Mode Control
ReferenceVoltage
MUX
DACShiftRegister
Simplified Block Diagram
Bypass Mode
tmdatatmclk
Burn Bits
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EEPROM Programming
Simulate and find the best-fit trim code.Re-program the EEPROM register. Verify result.Cycle power and read back programmed data. Verify that the data is correct.Verify all electrical parameters.
EEPROMRegisterControl
Registers
Test Mode Control
ReferenceVoltage
MUX
DACShiftRegister
Simplified Block Diagram
Bypass Mode
tmdatatmclk
Burn Bits (Register)
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Trimming
Trim parameter folding
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Trim parameter folding
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Trimming
Trim parameter foldingReference Distributions
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Reference Distributions
VBG
temp25C
1.19V
100C
Part A Part B
0C
Code N
Code N-1
Code k
Code 2
Code 1
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Trimming
Trim parameter foldingReference DistributionsTrim Flow
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Trimming flow
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Execute() function
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