2. 1 Quartz Crystal : IQC procedures and Reliability Issues Arthur Lee Technical Director Copyright, 1999 © Hong Kong X’tals Limited.

3. Hong Kong X’tals Limited 2 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 !

4. Hong Kong X’tals Limited 3 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

5. Hong Kong X’tals Limited 4 The Structure of a Quartz Crystal Cover Base Silver Electrode on both sides Silver Epoxy Quartz Wafer ( Blank ) Sealed with Clean, Dry, inert gas Electrical Energy Voltage & Current Mechanical Energy Stress and Motion

6. Hong Kong X’tals Limited 5 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

7. Hong Kong X’tals Limited 6 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.

8. Hong Kong X’tals Limited 7 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.

9. Hong Kong X’tals Limited 8 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 ?

10. Hong Kong X’tals Limited 9 What is …. ??? Sleeping Crystals, and DLD Spurious modes ??

11. Hong Kong X’tals Limited 10 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 ).

12. Hong Kong X’tals Limited 11 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.

13. Hong Kong X’tals Limited 12 Crystal DLD Typical Example Changes due to Design limit, not because of poor process Kolinker KH1200 Test data At 10nW Rs=37 At 100uW Rs=31, non-ideal process, depending on applications, could be good or no good

14. Hong Kong X’tals Limited 13 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

15. Hong Kong X’tals Limited 14 Details in DLD or Sleeping Crystals See Handout for details, or Contact E-mail : HKXtals@HongKongCrystal.com for a separated paper.

16. Hong Kong X’tals Limited 15 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 !

17. Hong Kong X’tals Limited 16 Couple modes at Room temperature Main mode : AT Cut, Thickness Shear All other couple modes are NOT AT Cut, Thickness Shear mode Couple Mode is also known as : Spurious mode inharmonic mode unwanted mode

18. Hong Kong X’tals Limited 17 Couple modes at Room temperature Good Example Main mode : AT Cut, Thickness Shear Kolinker KH1200 Test data

19. Hong Kong X’tals Limited 18 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.

20. Hong Kong X’tals Limited 19 IQC -- Normal Level Add : –Drop Shock –Vibration ( option for automobile industry ) –Accelerated Aging Test Refer to hand out for detail chart All environmental condition, e.g. Drop Shock, Aging, Vibration, etc Test after environmental condition, For all electrical parameters Compare results with specified limits

21. Hong Kong X’tals Limited 20 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 MHz50 cm –>= 12 MHz35 cm Spring Mount –Below 16 MHz75 cm –>= 16 MHz50 cm

22. Hong Kong X’tals Limited 21 Accelerated Aging Test Standards Industrial Standards, usually –105 degree C, 7 days, or –85 degree C, 30 days, or 1000 hours 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.

23. Hong Kong X’tals Limited 22 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.

24. Hong Kong X’tals Limited 23 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 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

25. Hong Kong X’tals Limited 24 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.

26. Hong Kong X’tals Limited 25 Temperature Cycle Good Example Kolinker KH1200TS Test data

27. Hong Kong X’tals Limited 26 Temperature Cycle Bad Example Kolinker KH1200TS Test data

28. Hong Kong X’tals Limited 27 Couple modes over temperature Bad Example Kolinker KH1200TS Test data

29. Hong Kong X’tals Limited 28 Couple modes over temperature When Temperature Change : Frequency changes, ESR changes Main mode All other couple modes change according to the TC curves of each of their own modes

30. Hong Kong X’tals Limited 29 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.

31. Hong Kong X’tals Limited 30 Couple modes over temperature Good Example Kolinker KH1200TS Test data

32. Hong Kong X’tals Limited 31 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 ?

33. Hong Kong X’tals Limited 32 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 ….

34. Hong Kong X’tals Limited 33 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.

35. Hong Kong X’tals Limited 34 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.

36. Hong Kong X’tals Limited 35 Your tester with the PCBA of the product Oscillator Circuit buffer Do Not Test here : avoid loading the oscillator Test at other functional check point to avoid loading the oscillator. Check for function including frequency, pullability and amplitude Socket for crystal : Low Inductance Low stray capacitance Prefer gold plated Obtain from your crystal supplier Safety Factor for ESR : Resistor = about 2  maximum ESR at room temperature DUT

37. Hong Kong X’tals Limited 36 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.

38. Hong Kong X’tals Limited 37 Difference : Self-build testers and Standard tester

39. Hong Kong X’tals Limited 38 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

40. 39 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 : HKXtals@HongKongCrystal.com FAX : ( 852 ) 24985908 Copyright, 1998 © Hong Kong X’tals Limited