Sleeping Crystals and DLD Drive Level Dependency Copyright

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Sleeping Crystals and DLD ( Drive Level Dependency ) Copyright, 2000 © Hong Kong

Sleeping Crystals and DLD ( Drive Level Dependency ) Copyright, 2000 © Hong Kong X’tals Limited. http: //www. Hong. Kong. Crystal. com Arthur Lee Technical Director 1

What is Sleeping Crystals ? ? ? Sleeping crystal is a well known phenomenon

What is Sleeping Crystals ? ? ? Sleeping crystal is a well known phenomenon in the 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 ( usually with power removed), it sleeps again --- not functioning. The time that it begins to sleep again is unpredictable, could be minutes or months. Hong Kong X’tals Limited 2

Sleeping Crystals make ambiguous failures ! This phenomenon is one of the reasons why

Sleeping Crystals make ambiguous failures ! This phenomenon is one of the reasons why when a crystal user finds a faulty crystal, returns it to the crystal maker, but the failure analysis reports says the crystal is good. Most likely the sleeping crystal was “woken up” by either the mechanical shock / vibration during transportation, or being tested at a relatively high drive level during failure analysis. ( note : there are many other reasons for these send-faulty, return-good situations, sleeping crystal is one of them ). Hong Kong X’tals Limited 3

I have been using crystals for years. Why I haven’t ever seen a Sleeping

I have been using crystals for years. Why I haven’t ever seen a Sleeping crystal. Hong Kong X’tals Limited 4

Slow Starting Crystals = Sleeping Crystals !? ? Decades ago, electronic circuits worked at

Slow Starting Crystals = Sleeping Crystals !? ? Decades ago, electronic circuits worked at higher voltages and lower frequencies. Hence, crystals operated at higher drive levels ( say, 1000 W or above ). The high drive levels of these circuits woke up the crystal every time it was switched on, hence, in the olden days, this sleeping phenomenon was not a big problem. However, the high drive level of these circuit still require some time ( from m. Sec to Seconds ) to wake up the sleeping crystal. That is why some engineers call these crystals “Slow Starting”. Hong Kong X’tals Limited 5

Nowadays application are more demanding ! v The lower voltage of application circuits usually

Nowadays application are more demanding ! v The lower voltage of application circuits usually result in lower drive levels, v The higher operating frequencies, hence more phase lag in circuits usually result in lower drive level ( due to lower load capacitance CL ), v Applications now demand faster start up time, say for example : VGA display cards, USB devices with hot plug feature, PC card with hot plug feature, etc. , v Battery operated devices with power saving mode demand very fast start up time, say for example : PDA, mobil phones, cordless phones, and pagers that switch on and off in milli-seconds cycles so as to save battery power. Hong Kong X’tals Limited 6

Why do Crystals sleep ? The root cause of sleeping crystals is contamination in

Why do Crystals sleep ? The root cause of sleeping crystals is contamination in the various production stages. Contamination of quartz crystals is not only limited to dirt particles, but traces of moisture, gases, oils, etc are also considered as contamination. Hence, the cost of controlling contamination in all the production stages is high, and it is some times very difficult to locate the source of contamination. Hong Kong X’tals Limited 7

The Structure of a Quartz Crystal Cover Quartz Wafer ( Blank ) Any Silver

The Structure of a Quartz Crystal Cover Quartz Wafer ( Blank ) Any Silver Electrode contamination will affect on both sides performance of the crystal, Silver Epoxy including : Sealed with Clean, Dry, inert gas Base Hong Kong X’tals Limited Contamination on the quartz surface and, inside the structure. 8

Hot topic in the industry Today, sleeping crystals are still a hot topic in

Hot topic in the industry Today, sleeping crystals are still a hot topic in the industry and a lot of research work is still being done by a lot of crystal makers. However, not all crystal makers know how to avoid producing sleeping crystals. That is why some of them do not like to talk about this topic. Hong Kong X’tals Limited 9

Is there a cure for Sleeping Crystals ? Unfortunately there is no cure, a

Is there a cure for Sleeping Crystals ? Unfortunately there is no cure, a sleeping crystal will sleep again, even after excited / woken up. The sleeping state is the crystal’s natural stable state, it will return to this stable state after external excitation is removed for some duration. There is no way that a Sleeping crystal can be cured and become a non-sleeping crystal again. There is no way to remove contamination after the manufacturing process. v. There is NO cure ! Hong Kong X’tals Limited 10

High Driving -- by Crystal Makers ? ? Some crystal makers “high drive” their

High Driving -- by Crystal Makers ? ? Some crystal makers “high drive” their crystals in their production ( driving the crystal with a very high drive level ) so as to wake up all the crystals before outgoing test hence, achieving a higher output yield. This means delivering sleeping crystal to users, but these crystals will sleep again eventually. Hong Kong X’tals Limited 11

High Driving – wrong specification !? For the same reason, you should specify the

High Driving – wrong specification !? For the same reason, you should specify the operating drive level of your circuit correctly, so that good crystal makers will not test ( drive ) the crystal inappropriately. Say for example, if your circuit operates the crystal at 50 W, but you specify 1 m. W ( by copying from old specification sheets ), then you are instructing your crystal makers to wake up ( high drive ) all the sleeping crystals during their production, and final outgoing test. Please note that 1 m. W is considered as a very high drive level nowadays, due to the much lower drive levels in application circuits and much smaller crystal sizes than older packages. If you have difficulty specifying the drive level of your circuit, send your PCBA to your crystal maker for measurement. Hong Kong X’tals Limited 12

How to detect Sleeping Crystals ? The major difficulty in detecting a sleeping crystal

How to detect Sleeping Crystals ? The major difficulty in detecting a sleeping crystal is : once it is woken up, it behaves like a good crystal, and the time required to wait until it sleeps again is unpredictable ( could be seconds, minutes, days, or weeks ). We have to detect sleeping crystals indirectly, making use of DLD ( Drive Level Dependency ) of the crystal. Drive level dependency of a crystal is caused by the same root cause as Sleeping Crystal, contamination, but less serious. Hong Kong X’tals Limited 13

The DLD characteristics of an ideal crystal Over a wide drive level range (

The DLD characteristics of an ideal crystal Over a wide drive level range ( decades of drive level ) the ESR and frequency of the crystal changes very little until the drive level reaches its structural limit. However, a Sleeping crystal may show the same characteristic after a large external excitation. When Drive Level is below the structural limit, ESR changes very little, or no change. When Drive Level is higher than the structural limit, ESR increases dramatically, this is normal. Hong Kong X’tals Limited 14

The DLD characteristics of some non-ideal crystals : Below the structural maximum drive level,

The DLD characteristics of some non-ideal crystals : Below the structural maximum drive level, the ESR and frequency of a non-ideal crystal changes a lot ( ESR changes by several times, Frequency changes by several tens of ppm ) due to contamination in various production processes. When Drive Level is higher than the structural limit, ESR increases dramatically, this is normal. The four crystals shown here are bad DLD crystals due to large ESR change Hong Kong X’tals Limited 15

Non-repeatability dilemma To measure this DLD characteristic, the maximum measurement drive level specified in

Non-repeatability dilemma To measure this DLD characteristic, the maximum measurement drive level specified in the range must be high enough to excite ( wake up ) the crystal. Hence, after measuring the first time, the DLD characteristic of the same crystal changes ( usually appears better ). And, if the maximum measurement drive level is high enough, the crystal will be totally woken up, and may perform like an ideal crystal for some time ( like the above ideal DLD curve ). Hence, this measurement is NOT repeatable, and we should only rely on the first measurement result. Hong Kong X’tals Limited 16

Important note If the DLD characteristic of a crystal does not change with time,

Important note If the DLD characteristic of a crystal does not change with time, nor does it change with external excitations, then, this crystal is NOT a sleeping crystal ( it may be a poor DLD crystal, but not a sleeping crystal ). Depending on the application circuit’s operating drive level, this poor DLD crystal may or may not be a good crystal : v if the application circuit works fine with the ESR at the operating level ( including consideration of start up speed), this is a good crystal, else, v if the application circuit can not operate with the ESR at the operating drive level ( including consideration of start up speed), then this is a failure. Hong Kong X’tals Limited 17

At 10 n. W Rs=37 At 100 u. W Rs=31, non-ideal process, depending on

At 10 n. W Rs=37 At 100 u. W 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 KH 1200 Test data Hong Kong X’tals Limited 18

Time characteristic of DLD ESR at low Drive Level, or DLD-d. Rs, or DLD-d.

Time characteristic of DLD ESR at low Drive Level, or DLD-d. Rs, or DLD-d. Fs The DLD characteristic of a crystal may change with time, and will also be changed by external excitation. Excited by external small stimulation : slightly waken up Hong Kong X’tals Limited Sleep mode : stable steady state Waken mode : Unstable state Time Excited by external larger amplitude stimulation : much waken up 19

Gamma ratio test for DLD When we attempt to test a crystal chosen at

Gamma ratio test for DLD When we attempt to test a crystal chosen at random, can we determine the status of the crystal : sleeping ? waken ? or semiwaken up ? Or, how to device test methods that can better test a crystal’s Sleeping ( non-repeating DLD ) characteristic? The answer to the question is not simple. Some crystal engineers devised a test method focusing on the ESR ratio instead of the absolute change in ESR, hoping to solve the problem by comparing the ratio of ESR ( and frequency ) between several measurements taken at different drive levels. Hong Kong X’tals Limited 20

Gamma ratio test for DLD The test method compares the ratio of ESR, and

Gamma ratio test for DLD The test method compares the ratio of ESR, and frequency change between the 1 st : 2 nd, and 1 st : 3 rd measurements. Where : 12 = ESR of 1 st measurement / ESR of 2 nd measurement <= specified limit 13 = ESR of 1 st measurement / ESR of 3 rd measurement <= specified limit ( Fr of 1 st measurement – Fr of 2 nd measurement ) <= specified limit ( Fr of 1 st measurement – Fr of 3 rd measurement ) <= specified limit Hong Kong X’tals Limited 21

Multiple measurement points Some engineers further modify this method with multiple measurement points so

Multiple measurement points Some engineers further modify this method with multiple measurement points so as to detect ESR / Frequency changes in between the minimum and maximum drive levels. For details, please refer to the IEC standards 444 -6. These methods are still under evaluation in the crystal industry, and there is still, as yet, no final conclusion, especially when the discussion has to cover a wide range of applications : military, professional, industry and commercial. The Kolinker KH 1200 network analyzer provides a convenient user interface for crystal engineers to further investigate these methods. Hong Kong X’tals Limited 22

Definition of Sleeping --Relationship of Sleeping and DLD The ESR and frequency of a

Definition of Sleeping --Relationship of Sleeping and DLD The ESR and frequency of a commercial grade crystal change inevitably with drive level. Some may change by as little as 1 Ohm, while some may change by a few hundreds or even a few K Ohms, or the ESR becomes so high that even professional crystal measurement systems are not able to measure the ESR, and indicate an “unstable crystal”. But will a poor DLD crystal sleep ? Or, how poor is the DLD of a sleeping crystal ? Or, how …. Hong Kong X’tals Limited 23

Relationship of Sleeping and DLD Structural Limit ( Design Limitation ) Other Reasons (

Relationship of Sleeping and DLD Structural Limit ( Design Limitation ) Other Reasons ( unknown ) Hong Kong X’tals Limited Poor DLD characteristic Contamination ( Non-ideal process ) Fail at operating Drive level Nonrepeatable DLD ( Difficult to measure ) Repeatable DLD Sleeping Fail below operating Slow Starting & Sleeping Drive Level Pass both of the above Good Crystal, but safety margin should be set in DLD specification, to avoid potential Sleeping crystal Fail at operating Drive level Simple Failure, easy to detect Fail below operating Slow Starting, easy to detect Drive Level Pass both of the above Good crystal 24

Rough Definition Roughly speaking, Sleeping Crystals are crystals with Nonrepeatable DLD characteristic and fail

Rough Definition Roughly speaking, Sleeping Crystals are crystals with Nonrepeatable DLD characteristic and fail to operate in the application circuit at either: v the operating drive level of the application circuit, or v the drive level roughly 5 to 10 times below the operating. Practically, this definition is correct, but quite dependent on the characteristic of the application circuit that it is not easily understandable by most crystal users. Unfortunately, there is no clear formal definition for a Sleeping crystal in the crystal industry. Hong Kong X’tals Limited 25

Crystal Measurement Precautions v. DLD measurement v. Measurement results verification v. Failure analysis v“Fs

Crystal Measurement Precautions v. DLD measurement v. Measurement results verification v. Failure analysis v“Fs stable, FL unstable” crystals Hong Kong X’tals Limited 26

DLD Measurement Precautions To further eliminate the possible measurement error due to equipment (

DLD Measurement Precautions To further eliminate the possible measurement error due to equipment ( FL and RL measurement error ) : Do not measure DLD-d. FL, or DLD-d. RL … etc v. For crystal below 100 MHz, measure DLD-d. Fr, and DLD-d. Rr, and v. For crystal at 100 MHz or above, measure DLD-d. Fs, and DLDd. Rs Hong Kong X’tals Limited 27

Measurement Result verification Measurement results verification ( including all other parameters ) : When

Measurement Result verification Measurement results verification ( including all other parameters ) : When verifying measurement results by re-measuring the crystal, bear in mind that the crystal may have been woken up after the first measurement. It is a good habit to leave the crystals for a few days before any re-measurement. v Note : The same applies for all oscillators. Hong Kong X’tals Limited 28

Failure analysis Precaution When performing failure analysis, bear in mind the parameters of a

Failure analysis Precaution When performing failure analysis, bear in mind the parameters of a crystal with “Poor aging characteristics” also change with time, but poor aging crystals could not be woken up by excitation. Of course, some bad crystal may have both failure modes : poor aging and poor DLD. v Note : The same applies for all oscillators. Hong Kong X’tals Limited 29

“Fs stable, FL unstable” crystals v Some crystals when measured for FL will show

“Fs stable, FL unstable” crystals v Some crystals when measured for FL will show “Unstable”, but when measured for Fs, or Fr will show stable. v Most likely, these crystals have DLD problems. In such an event, use the DLD graphic scan in KH 1200 to find out the DLD characteristic of such crystals. Hong Kong X’tals Limited 30

Technical Support from HKC Send HKC your production failures Send us your latest PCBA

Technical Support from HKC Send HKC your production failures Send us your latest PCBA for crystal specification verification. Web Page : http: //www. Hong. Kong. Crystal. com E-mail : HKXtals@Hong. Kong. Crystal. com FAX : ( 852 ) 24985908 Copyright, 2000 © Hong Kong X’tals Limited 31