Download Quartz Crystal

Quartz Crystal :
IQC procedures
and Reliability Issues
Copyright, 1999
©
Hong Kong X’tals Limited.
Arthur Lee
Technical Director
1
What is a Quartz Crystal ???
• Production Engineers :
– It is the first component you replace
when you have a failure board !
• Purchasing Officers :
– It is a component that you could
never get a reliable vendor !
• R&D Engineers :
– It is a mysterious little black box !
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What is a
Quartz Crystal ?
A crystal is a Piezo-Electric
Device, i.e. :
Energy is converted between
electrical and mechanical,
millions of times per second.
Hence, its characteristic is very different form
other components, as oppose to :
• Resistor -- Pure Electrical
• Screw -- Pure mechanical
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The Structure of a
Quartz Crystal
Cover
Silver Electrode
on both sides
Quartz Wafer
( Blank )
Silver Epoxy
Sealed with
Clean, Dry,
inert gas
Base
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Mechanical Energy
Stress and Motion
Electrical Energy
Voltage & Current
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What is special with a
Quartz Crystal?
Due to the Electro-mechanical nature, a quartz
crystal has some unique characteristic that
require attention, such as :
–
–
–
–
–
–
Sleeping Crystals ( DLD characteristic )
Spurious modes at room temperature
Drop Test / Shock and vibration Tests
Aging ( Frequency and ESR drift )
Temperature Cycle
Over Temperature characteristic
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5
Full Analysis at IQC ?
• A full analysis on all crystal parameters,
especially the reliability performance, requires a
lot of effort and equipment.
• The function of IQC is to check some critical
parameters that may affect your products’
quality / performance, but NOT to act as your
suppliers’ outgoing QA.
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What parameters can be
included in IQC ?
– All room temperature parameters, including
• Sleeping Crystals ( DLD characteristic )
• Spurious modes at room temperature
– Drop Test / Shock and vibration Tests
– Aging ( Frequency and ESR drift )
• Optionally depending on package type and
vendor, solderability test may be needed.
• Over temperature test and thermal cycle test are
usually skipped due to cost and time.
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IQC -- Relaxed Level
• AQL depends on crystal user or
crystal supplier, typical 0.4%, or
0.15%; or optional C=0 Sampling
method
• Depending on Crystal user's company
policy, data of 10 pcs pass crystals,
and any failure should be printed out
and kept together with supplier's
batch code for tracibility.
• Skip Drop Shock and Accelerated
Aging tests as compared to Normal
Level, so as to reduce IQC work load
Mil-Std-105D Level I,
Sampling for each incoming batches
Visual Check for marking and outlook
Electrical Parameter Test using KH1200
includes :
DLD, Spurious, FL, ESR, Co, C1, Ts,
( and optional DL=FL1-FL2 etc.. )
Pass ?
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What is …. ???
• Sleeping Crystals, and DLD
• Spurious modes ??
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Sleeping Crystals
• Sleeping crystal is a well known phenomenon in Crystal
Industry :
– The Crystal will NOT start, but after the crystal is started by some
mechanical or electrical excitation, it works fine for some time, then, after
some unknown time, it sleeps again – not functioning.
– The time that it begins to sleep again is unpredictable, could be minutes or
months.
– Not all crystal makers know how to avoid producing sleeping crystals, that’s
why not many crystal makers like to talk about this.
• Root Cause : Improper Cleanliness
• Cure : None, a sleeping crystal will sleep again.
• Test Method : DLD, or high drive
( note high drive is a test, not a cure ).
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DLD or Starting ESR
• Same root cause as Sleeping Crystal, less serious.
• If your circuit has starting problem, you should specify
extra requirement of ESR at a lower drive level.
• This specification depends on your circuit’s drive level, and
starting gain.
• Do NOT over specify, it costs.
7
6
5
4
ESR
3
2
1
0
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Drive Level
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At 10nW Rs=37
At 100uW Rs=31, non-ideal process,
depending on applications, could be
good or no good
Crystal DLD
Typical Example
Changes due to
Design limit, not
because of poor
process
Kolinker
KH1200
Test data
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12
Typical DLD Specification
• Ask your crystal vendor the operating Drive level (DL) of
your circuit, and also whether your circuit has a good
starting gain.
• If your circuit has a good starting gain, specify :
– DLD test range : from 2.5nW/Ohm to
1 µW/Ohm or operating DL ( whichever the lower);
and, ESR change in above power range <  ( 20% to 120%,
depending on ESR )
• If your circuit does not has a good starting gain :
– discuss with your vendor.
• This specification safeguard against Sleeping Crystal with
very high safety factor, hence may affect cost
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Details in DLD
or Sleeping Crystals
• See Handout for details, or
• Contact E-mail : [email protected]
for a separated paper.
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Spurious Modes ( Couple Modes )
• Couple modes always exist !
– Couple modes are caused by energy coupling from the main mode of
vibration ( AT cut thickness shear ) to other unwanted vibration mode. Just
like when you hit a guitar wire, other then the fundamental frequency, it will
always produces other harmonic and inharmonic frequencies.
• Must specify Minimum ratio of :
ESR(worst unwanted mode) / ESR(operation) > 2.5
• ( to 10 times for very demanding applications )
• If the unwanted modes are too active, the oscillator may :
– jump from one frequency to another, or too much jitter / phase
noise
– produce impure spectrum that may jam your circuits.
• Do Not over specify, it costs !
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Couple modes at Room temperature
Main mode : AT Cut,
Thickness Shear
1.2
1
0.8
Couple Mode is also
known as :
•Spurious mode
•inharmonic mode
•unwanted mode
0.6
0.4
0.2
0
All other couple modes are NOT AT Cut,
Thickness Shear mode
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Couple modes at Room temperature
Good Example
Main mode : AT
Cut, Thickness
Shear
Kolinker
KH1200
Test data
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Deficiency of Relaxed Level
• Only Room temperature test
• No Drop Test, Aging Test, and over temperature
test
• Do Not forget to set up Spurious Test and DLD
test, this helps.
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IQC -- Normal Level
• Add :
– Drop Shock
– Vibration ( option for
automobile industry )
– Accelerated Aging Test
All environmental condition,
e.g. Drop Shock, Aging, Vibration, etc
Test after environmental condition,
For all electrical parameters
• Refer to hand out for
detail chart
Compare results with
specified limits
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Drop Test
• Very Important Reliability Specification
• Do Not over specify, it costs !
– Different for different grade of crystals and different application
and different vendors.
• Typical Drop shock performance :
Clip Mount :
– Below 12 MHz
– >= 12 MHz
50 cm
35 cm
Spring Mount
– Below 16 MHz
– >= 16 MHz
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75 cm
50 cm
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Accelerated Aging Test Standards
• Industrial Standards, usually
15
– 105 degree C, 7 days, or
– 85 degree C, 30 days, or 1000
hours
10
5
ppm
• These require too much time
• Aging test check for excess
stress and contamination in
the crystal, if too serious, the
crystal may become dead
after some time.
0
-5
1st 2nd 3rd 4th 5th 6th 7th
day day day day day day day
-10
-15
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Short Cut :
Accelerated Aging Test
• Usually :
– 85 degree C to 120 degree C,
– for 1 to 2 hours
– Then check for difference before and after test, usually :
• Difference in Fs : < +/- 5 to 10 ppm
• Difference in ESR : < +/- 10 to 20% + 2 Ohm
• Important note :
– Since this is not a standard test, some crystal vendor agree, some do not.
You will have to discuss with them.
– You need a good instrument to test, the R&R ( Repeatability and
Reproducibility ) of the instrument should be well within the
requirement.
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IQC -- Tighten Level
• Add :
Room temperature parameter
record between each
environmental condition, and
compare difference of Fs and
ESR.
• Usually, difference in Fs < 5 to
10 ppm, and difference in ESR <
5 to 20% + 2 Ohm
• Note : This is too tight for
commercial grade applications
• Refer to hand out for detail chart
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Test before environmental condition,
For Fs and ESR
One environmental condition, e.g. Aging
Test after environmental condition,
For Fs and ESR
Compare difference between
: Before and after of each
individual condition
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Reliability Issues
Not covered by above IQC
• Temperature Cycle
– Usually NOT specified and tested by crystal vendor for
commercial grade crystal
• Over Temperature Characteristic
– For commercial grade, usually only specified as ??
ppm over temperature
– But the crystal may change dramatically over some
narrow temperature ranges.
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Temperature Cycle
Good Example
Kolinker
KH1200TS
Test data
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Temperature Cycle
Bad Example
Kolinker
KH1200TS
Test data
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Couple modes over temperature
Bad Example
Kolinker
KH1200TS
Test data
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Couple modes over temperature
Main mode
1.2
1
0.8
0.6
0.4
0.2
When Temperature Change :
Frequency changes, ESR changes
All other couple modes change
according to the TC curves of
each of their own modes
0
1.2
1
0.8
0.6
0.4
0.2
0
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The Frequency and ESR of the
Main mode is affected by how the
other couple modes are changing
over temperature.
If a crystal is not designed
properly, the crystal may exhibit
frequency jump or severe ESR
change over temperature.
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Couple modes over temperature
Good Example
Kolinker
KH1200TS
Test data
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IQC Consideration
• Reliability issues that you may include into
your IQC procedures :
•
•
•
•
DLD -- Sleeping Crystals
Spurious mode
Drop Shock / Vibration
Accelerated aging
• Reliability issues that will cost you if you
include into your IQC procedures :
• Over temperature characteristic
• Temperature Cycle
• Solderability
• What kind of tester do I need ?
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Standards for the Crystal Industry
• Measurement Standards
– IEC 444 is the commonly recognized and adapted by the
crystal industry
– Sometimes, EIA 512 is used in very high frequency ( above
200 MHz )
• Specification Standards
– There are various standards ( e.g. Mil-Std 3098 ... ), but most
of them are outdated, and not suitable for nowadays’
application and crystal packages
– An example is : drive level = 1 mW is well too high for
nowadays crystal packages like HC-49U, HC-49US, 57
SMD, UM-1, UM-5 ….
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Measurement Instrument
• IEC 444 Measurement Standard
– IEC 444 describes how crystal can be measured with transmission
technique. It also defines explicitly a matching network to match the
crystal impedance to the 50 Ohm coaxial cables commonly used in most
network analyzers
– For measuring, Co, FR and ESR, it is not too difficult to follow.
– However, for FL and other parameters, it is extremely difficult for
electronic product engineer to follow through all the details and develop
compensation techniques for specific test jig and fixtures.
• There are test instruments commercially available complying
with this standard.
– The discussion and measurement herein are based on the Kolinker
KH1200 Pi network crystal measurement system.
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Can I build my own tester ?
• Yes, but you must do it properly.
– Do NOT use any test circuit other than EXACTLY the same
one as the particular product.
– Do NOT target to build some standard general test jig that
can measure crystal parameter accurately for all types of
crystal. You will have big difficulties in determining phase
shift and stray component compensation. Usually, most
crystal vendors will have difficulty in accepting readings
from such testers.
– It is acceptable if you have one tester for each model/series
of product, using the PCBA of the product.
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Your tester with
the PCBA of the product
Safety Factor for ESR :
Resistor = about 2
maximum ESR at room
temperature
Socket for crystal :
•Low Inductance
•Low stray capacitance
•Prefer gold plated
•Obtain from your
crystal supplier
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Do Not Test here :
avoid loading the
oscillator
Oscillator
Circuit
Test at other functional check point
to avoid loading the oscillator.
Check for function including
frequency, pullability and
amplitude
buffer
DUT
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Building your own tester
• Build ONE set of test jigs for each individual model/series. Use THE
PCBA of the product, target for a GO / NG test, not a parameter test.
• The extra Resistor is to safe guard against changes due to :
–
–
–
–
–
Power supply variations
Temperature change thus affecting the components on the PCB
Component tolerance in mass volumn
Start up time
The crystal’s ESR may change due to drive level, temperature
• However, the extra Resistor may induce extra stray impedance ( both
inductance and capacitance ) which affect frequency, so if you want
accurate frequency measurement, you may have to consider building 2
test jig :
– one without Resistor for frequency test
– one with Resistor for maximum ESR test
• Do provide one extra set to your crystal vendor for crystal specification
identification.
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Difference : Self-build testers
and Standard tester
IEC444 compliance instruments
Require One time investment
No need to build tester for each new
model
Easy communication with crystal
vendor
Easy second sourcing
Self-build testers
No one time investment
Have to build tester for each new model
More work required to communication
with crystal vendor(s)
More work required during second
sourcing
Require a good written specification for Send the tester to your crystal vendor, let
each type of crystal. Most of the time
him specify the crystal for you ( do this
you will have to send your PCBA to
with every new model, or every new
your vendor for specification
vendor )
verification.
Parametric test for better control
Simple GO/NG test
Both method acceptable by most crystal vendors
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Crystal Passing IQC,
but fail in Production !
• This is No good, some corrective action MUST be
done !
• Possible cause :
– Crystal quality problem not covered by IQC ( Improper IQC
procedures / coverage )
– Improper crystal specification ( matching )
– Improper testing instrument
– Problems with other components
• Contact your Crystal Vendor, see whether they could
give you proper support
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Technical Support from HKC
Send HKC your production failures
Send us your latest PCBA for crystal
specification verification.
Web Page : http://www.HongKongCrystal.com
E-mail : [email protected]
FAX : ( 852 ) 24985908
Copyright, 1998 © Hong Kong X’tals Limited
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