(ultra)acoustic in circuit component level crack detector? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2018, 01:51:12 pm
content: So you can get fractures in components that lead to failure, sometimes they are slow to propagate.Can you possibly make something like ultrasonic tweezers to get a profile of a part after its soldered down so you can basically use the tweezers are a VNA type device but that works with ultrasonic frequencies to see a mechanical change in a part?Or would the substrate give too much noise?i thought it might be as simple as getting some metal tweezers that are somewhat thick, mounting them to a compliant grip to isolate your hands (silicone rubber), and mount two of those cheap ultrasonic devices to it some how (the little cans with the mesh meant to be transducers that also happen to receive).The idea is that you would finish a PCB then measure the various SMD components like capacitors and then remeasure them as a part of inspection.Perhaps like after a burn in period to eliminate initial drift factors (but this is where the crack might form so I am not sure).Or you might need to cut the tweezers in half carefully with a jewelers saw and then bond them through a vibration dampener (so you measure the component), Maybe two different tools. It depends on the impedance of the component compared to the impedance of the junction its kind of like setting a VNA impedance I think?In lieu of complex dsp or pressure settings in measurements perhaps you can record the oscilloscope readout in a video form when a 'squeeze' test is performed to get rid of contact pressure related problems (since you get a a contact pressure sweep this way).I was hoping a crack might show up as a very visible anomaly. Maybe you can just bond a inductor thats going to be vibrated with a magnetic field then a real transducer. If you use a shielded inductor and shielded cable (maybe mu metal) it might reduce crosstalk through free space and limit it to magnetics.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 02:25:43 pm
content: Try it!

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2018, 02:27:45 pm
content: I don't want to waste my time if there is some kind of crack detector on the market already. I have serious doubts. And I don't know how to do the mechanical coupling well or good transducers to use. I know piezo is hard. And I don; thave a impedance analyzer.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 02:42:12 pm
content: People invent huge things and don't get a penny from them all the time. It's in many cases better to sit on your ideas until you have some capital. Or they will just get stolen from you.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2018, 02:56:40 pm
content: I am afraid the solder and board can have quite some effect on the ultrasonic properties. So chances are one would only see major defects and not those small initial ones. With ceramic caps, which would be my main target ther piezo electric properties of the capacitors make things more complicate, as there would be additional damping, that depends on the history of the part.The transducers of choice would be likely a piezo type. However those small part would need high frequencies - more like several MHz for 1206 size and more if smaller. So it is no am easy task.

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2018, 03:04:55 pm
content: Quote from: cdev on December 20, 2018, 02:42:12 pmyou know if its gonna be used as a maintenance check on an air liner or something its probably too big of an idea for meim not gonna charge for safety and reliability ideas like those IEC fuckers trying to make me pay like 3 grand to figure out how a lighting protection system for a building works. its fucking profiteering just like pharma companiesand its the holidays

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2018, 03:14:08 pm
content: Quote from: Kleinstein on December 20, 2018, 02:56:40 pmwell if you have a coupling capacitor on a PCB and you squeeze steel tweezers on it some how (or a clip that has a tension spring) how much energy would you need and what frequencies would be good?Does it matter if its mounted not right next to the clip part (so its like a tool like a LCR meter with the transducer being more in the handle?As for driving transducers could you use a LT1010 to drive a transformer (its from a app note) to step it up with some kind of impedance matching network? How about the receiver?What transducers would you use? Could a variable air capacitor be used to figure it out empirically?

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2018, 03:27:28 pm
content: They do make crack detectors which work using ultrasonics but I do not know about using them on such small structures.Cracks can be found in finished printed circuit boards using x-ray inspection.

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2018, 03:51:58 pm
content: Quote from: David Hess on December 20, 2018, 03:27:28 pmthats really hardcore and slow and expensive. I can imagine this being made cheap if it works. and fast and idiot proof.maybe you can even do that transform to bring it into the audio range and listen to it on headphones if you do FFT shifting and scaling. like break it into bins and shift em aroundor/also if its a in circuit maintenance test you might be able to beam it into smart glasses so you can see the spectrum while you work and inspect wiring and stuffthe book 'airframe' comes to mind, maybe it would be a use for smart computers if you talk outloud and it tabulates the data so you say like r17 looks good or even ask to see/ replay what you measured before if you store your maintenance data on a network drive or something.https://en.wikipedia.org/wiki/Airframe_(novel)maybe you can check crimps this way too?would be nice for a multimeter and oscilloscope/scopemeter too. i would actually get smart glasses if you can do that. and take something like siri seriously. you could actually focus on not frying half the board moving the probes around while you work, what we do now is antediluvian.

author: Benta
author_rank: Super Contributor
timestamp: December 20, 2018, 04:09:32 pm
content: I don't think the cheap, small round transducers will give you any joy. They operate at 40 kHz, the ultrasonic equipment I know of for materials checking operate in the 100s of kHz into the MHz range, very often with frequency sweeping.But it's certainly an interesting idea.

author: Mr. Scram
author_rank: Super Contributor
timestamp: December 20, 2018, 04:22:11 pm
content: Quote from: coppercone2 on December 20, 2018, 03:51:58 pmSounds good. Develop it!

author: ejeffrey
author_rank: Super Contributor
timestamp: December 20, 2018, 04:50:13 pm
content: What you are describing sounds very similar to scanning acoustic microscopy (SAM) which is a very common technique to look for cracks within materials. We use it to assess wafer bonding to look for voids in the bond. I think the tools to do this are quite complicated and expensive to actually get good results. I doubt you are going to have much luck with the cheap 40 kHz range finding piezo transducers and just shooting random ultrasound in an uncontrolled fashion, at least for something as small as an IC. It would be an interesting thing to try on some larger objects like some metal casting or something to see if you can get useful data out of a much simpler setup.

author: coppercone2
author_rank: Super Contributor
timestamp: December 20, 2018, 05:11:10 pm
content: what does this multi MHz transducer look like, cost, who sells one that can be attached to tweezers? i am guessing you can't vibrate a inductor for this purpose?or electrorestriction using a capacitor as a source and reciever. Are the amplitude levels too low to be measurable if you connect it to a high gain multi stage amplifier?

author: Benta
author_rank: Super Contributor
timestamp: December 20, 2018, 05:29:46 pm
content: Quote from: coppercone2 on December 20, 2018, 05:11:10 pmThis is something that the companies making this kind of equipment keep very close to their chest as trade secrets. Any dork can build electronics, but transducers are specialty knowledge. Off the shelf parts are unlikely.I know of piezo transducers, but magnetostriction types are also around, and perhaps the best option for your project.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2018, 05:44:24 pm
content: The transducers in the MHz range would likely be small (e.g. 1x1x0.2 mm³) piezos. Coupling to the sample would likely need something like a small cone or pyramid from a relatively hard metal or similar to protect the actual transducer and get a reasonable point like contact. Attaching this to a pair of tweezers could be tricky. I would consider his remotely similar to a crystal type record pickup, just a little smaller. So something to do under a microscope, maybe using wire bonding.The ones I once used had the transducer at the end of an 3.2 mm rod with a flat thin metal film on top and the actual transducer inside embedded in some plastics. I used those to check small samples (e.g. 2x2x3 mm³), using the sample corners for weak contact.I remember it was not that easy to find those transducers.

author: rhb
author_rank: Super Contributor
timestamp: December 20, 2018, 07:58:18 pm
content: This is a very interesting idea.Besides general reflection seismology, I have been heavily involved professionally in what is called "rock physics". This involves among other things making measurements of propagation velocity of small core plugs (1" x 2.5") using ultrasonic transducers at 1-2 MHz.I suggest testing the following arrangement:A long reach caliper with tranducers on each arm, a source and a receiver with a fairly soft pad on each arm to provide good coupling. the source on the one side of the PCB and component and the receiver on the otehr.A cracked device should show up as a large attenuation of the signal through the board.I suggest using some cheap 40 MHz 3rd overtone quartz xtals as transducers. At least to start with.I have a bin full and will see see if I can construct a satisfactory experimental setup. I have already found that by clamping the leads in a vise and pointing a Wen hot air gun at the case I could easily desolder and remove the metal can. The quartz xtal is fragile, so an experimental setup will not be easy. The ones I have are 0.15 mm thick.I'm going to start with using hot melt glue to bond a pair together and drive one while looking at the other with a scope.

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 08:15:54 pm
content: Maybe something like this would help?https://en.wikipedia.org/wiki/Quartz_crystal_microbalanceI stumbled across the concept a ways back when I was looking into ways to make my own sensors for environmental monitoring.There also seems to be a project involving QCMs athttps://openqcm.com

author: cdev
author_rank: Super Contributor
timestamp: December 20, 2018, 08:34:55 pm
content: Some of the Microchip PIC chips have a functional block, which can be used to do a great many things including ultrasound, which sounds to me a lot like what you are proposing. This is from Microchip Application Note AN1375 'see what you can do with CTMU' (Charge Time Measurement Unit)"46 Ultrasound Imaging As described in previous applications, the CTMU canbe used to measure the time between transmitted and reflected impulses.This information can be continuously fed in real time to a graphic processor, orprocessing application, to create an image. This can beimplemented directly as an ultrasonic microphone (# 2)or indirectly, through an ultrasonic pick-up (# 15)."Quote from: coppercone2 on December 20, 2018, 05:11:10 pm

author: rhb
author_rank: Super Contributor
timestamp: December 21, 2018, 12:11:43 am
content: Detecting the reflection from a cracked SMD part is going to be very difficult, if not impossible. The delay time will be on the order of a couple of microseconds or less for large parts. The only practical way to resolve that would be to use a chirp and cross correlation. A big problem with that technique is it requires a really fast ADC. But the LPC4370 might manage both the ADC and the processing. It's an M4 clocked at 204 MHz with an 80 MSa/S 12 bit ADC.I think the concept has potential, but it's seriously difficult to design an apparatus for this sort of thing.I got a box of parts in the post, so I have a 1.8 V logic safe continuity tracer to assemble this evening. Real rocket scienceAAA cell, 1.5 V piezo buzzer and two banana jacks. The buzzer gives a good tone at under 1 V, so I can use dead AAA cells.BTW If you look at the QCM sensors and look at the crystals I opened you'll see that they are identical except for the xtals I'm using are $10/100.

author: cdev
author_rank: Super Contributor
timestamp: December 21, 2018, 12:23:04 am
content: Maybe you can find out some useful info from time domain reflectometry app notes from the HP archive.http://hparchive.com/appnotes

author: rhb
author_rank: Super Contributor
timestamp: December 21, 2018, 01:02:36 am
content: Thank you for the suggestion, but I spent 30 years doing time domain reflectrometry as a research scientist and programmer in the oil industry. Reflection seismology is just the low frequency, elastic wave version. This is the high frequency, elastic wave version. The only thing that changes is the decimal points.The hard part is the sensor and data acquisition. The rest I can do in my sleep.The thing that makes it hard is the dimensions. Ideally you want the dimensions to be much larger than 1/10 of a wavelength. When you're talking about 0204 parts that means very high frequencies and consequently fragile transducers.Fortunately, I have lots of xtals, so if I destroy a couple dozen it's under $3.

author: eliocor
author_rank: Unknown
timestamp: December 21, 2018, 01:44:12 am
content: search forConfocal Scanning Acoustic Microscopy(CSAM). Some examples:https://sonoscan.com/resources/ami-overview/how-csam-technology-workshttps://www.tayloredge.com/reference/Electronics/Capacitors/MLC_FailureMechanisms.pdfhttp://www.us-tech.com/RelId/670224/ISvars/default/Finding_Singulation_Caused_Cracks_in_MLCCs.htmhttps://www.nanolabtechnologies.com/c-sam-imaging/

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2018, 02:05:38 am
content: if there is a crack in the capacitor won't the magnitude just be less (high impedance connection)?Electrically/equivilantly what does the impedance look like here at the frequencies we are discussing?Like the solder joint/pcb under capacitor/solder joint interface has a impedance of X ohms and the ceramic bit has a impedance of Y ohms.Can you ball park the X and Y assuming its just simple resistance so I can get an idea of the dynamic range?If their similar maybe you can just do a scalar so its like 100 ohms in parallel vs 100 ohms or if its cracked 1000 ohms in parallel with 100 ohms. Then if its wrong you can maybe do something like resolder the joint then measure it again to make sure its not a solder joint fracture.a VNA measurement would be best but I also thought it would be hard.Is mechanical reflection just much more sensitive or are you thinking about trying to locate where the crack is rather then that there is a crack (for this kind of test we don't need to estimate where it is, the part is screwed if you touch it up and the crack is still there).If you can do it that way, and use cheap transducers, you could just use like three different frequencies, get RMS values through filters / analog network on a simple ADC, make a FFT, frequency shift it to like 3 diff frequencies (50Hz, 500Hz, 5000Hz) and play it, and it might be weird enough that if they dance around it gives you a different sound thats not really representative of whats going on but that something is off.I doubt you would want to trust tweezers to try to make a TDR of this thing, you could remove the part and analyze it under a specialist machine if you care or just replace it.I imagined a very fast tool for checking a buncha decoupling capacitors an stuff quick on a big PCB.I am no geophysicist but I thought that measurement relied on reflection because you can't get a receiver probe that can actually get you any scalar data unless you bury it real deep, in this case the part is part of a parallel circuit with the substrate. A S21 measurement rather then the S11i am not saying not to shoot for the stars with a reflection measurement but i wanna know the options and electrical equivalents of what is happening/ I do not want to deal with a 200MSPS ADC either. At all. Or a cortex.

author: rhb
author_rank: Super Contributor
timestamp: December 21, 2018, 03:36:37 am
content: I'd like to suggest we back up and start over.The fundamental problem is how does one efficiently identify SMD components with internal cracks or solder joint cracks. It's pretty clear that this is a significant cause of failures.And how does one do this without having service data for the board in question?SMD has given us the ability to put large complex systems on a single board. So they should be easier to repair at component level. And would be if schematics were available.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2018, 04:41:00 am
content: I think knowing what the impedance/bode plots look like for cracked components could bring alot of light into this matter to see what the dynamic range requirements, loss, power, frequency, etc should be to aid in engineering some kind of sensor dataat least the tool is a fun project and you could probably write a entire book on the test methodology but its not appealing to do so unless you have a toy to play with. too boring to work out that level of detail for me unless I know there is a method at least. this idea picked up alot of hype with alot of different engineers and sensors are funmy understanding of the mechanical process here is probably like an order of magnitude off which makes this extremely difficult to think about, i don't think many people know about ultrasonic wave propagation in ceramics or anything like that.i will rename this thread to mechanical crack detector because i am sure there are a slew of RF methods to maybe find it. i think this idea is more interesting to think about because its a cool gadget that people might find appealing to work on because you modify tweezers and stuff rather then more complex stuff that makes you feel under equipped.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2018, 04:58:53 am
content: also knowledge of impedance units and values in this area will help in designing any sort of test system that is mechanicali do see merits for RF but if you want to measure like a inductor or diode or something its going to get really hairy, the mechancial method should work in circuit on anything even while powered I thinkcorrect VNA and even ohm setup (range selection) always depends on measurement impedance.the similar wave behavior of electrical and mechanical system should make this useful to know

author: rhb
author_rank: Super Contributor
timestamp: December 21, 2018, 12:54:53 pm
content: I don't think that you could get satisfactory mechanical coupling with tweezers on one side of the board. That also would not detect a solder joint crack between the board and the device.The correct electrical analogy is a transmission line. The presence of cracks will attenuate the signal transmitted through the part and the board.A significant complication is applying enough force to get good coupling, but not so much force that it closes the cracks. And when I look at the 0.15 mm thick xtals I wonder how one can mount them so they vibrate but not break them.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2018, 12:57:07 pm
content: maybe rubber bands? a spring should be linear too, you can add one to tweezers

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2018, 01:18:30 pm
content: Attaching the probes would be a big problem, as too little force would cause poor contact and possible false alarm. To much force could cause the transducers to wear out fast.With many parts on a board I am afraid individual testing with a contact sensor would be not practical as it takes a long time with manual handling and much wear on the sensors. So if at all it would be something for very high requirements where they can pay something like $10 extra per part for the test. The more practical test would likely be high resolution X-Ray.The is some kind of ultrasonic microscopy available already:https://www.ksisam.com/acousticmicroscopy-en/technology-transducer.phpDepending on the circuit one could also do an electrical test under mechanical load to the board. Some cracks would show up as kind of jumps / spikes.

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2018, 01:34:14 pm
content: hmm if i wanted to experiment further, how would i crack ceramics to make test samples?

author: coppercone2
author_rank: Super Contributor
timestamp: December 21, 2018, 03:21:51 pm
content: What are the mechanical units for loss from friction and loss from radiation (like ohms and radiation resistance)?

author: rhb
author_rank: Super Contributor
timestamp: December 22, 2018, 12:46:55 am
content: I was stuck in a waiting room all day and had a long think on the subject. It's highly unlikely that the idea can be made to work. The frequency would have to be so high that I don't think mechanical transducers exist that can do it. The problem is the small size of parts and the size vs wavelength required for resolution.Suppose the compressional velocity is 8333 ft/s (water is 5000 ft/s). That's 100,000 inches per second. So at 1 MHz a wavelength is 0.1" and at 10 MHz it's 0.01". To get 0.01" resolution we'd need a signal at 40 MHz or higher. To make matters worse, even at 13 MHz, the transducer is so small and fragile that putting a strong enough signal into the xtal will probably break it.I'm also very doubtful about attenuation as it would be hard to distinguish poor coupling from a cracked part.I'm going to do some experiments with the xtals I uncanned, but the very narrow response at 13 MHz will make the signal processing very difficult for any type of reflection processing.Experiments to test:Response of the bare xtal to a minimum width impulse from my 33622AResponse with a small piece of PCB glued to the xtalResponse of a 2nd xtal glued to the PCB as a receiver.It's very likely that the loading by the PCB will either completely kill the impulse response or shift the frequency so low that even the transmission delay time through the PCB will be unresolvable using an 8 bit DSO.

author: coppercone2
author_rank: Super Contributor
timestamp: December 22, 2018, 04:31:11 am
content: how many bits do you need? is it really that hard so long you don't need microwave level response or complex DSP or all that back end oscilloscope stuff? or do you mean triggering issues with memory storage? Can't you do some kind of predictive sampling triggering based on process time constants? or multiple filtered channels in sync? not sure i am understanding the problem can you make a drawing?What kind of dynamic range and resolution would it need in terms of signal acquisition. It would be actually interesting for me because as of yet any kind of signal sampling higher then something like 500KSPS has been utterly uninteresting for me. I like the slow slower sensors related to thermodynamics and chemistry that don't really need a sample speed higher then like 100KSPS even with the filters and decimation.i am not sure what exactly you are getting at because I am getting shit about lasers on google and its 4am but keep in mind there is literally no real time data accuracy requirement is, you could do various things to the signal and resend impulses with different reciever setups till you got something that looks right if the process is so complicated it requires ridiculous dynamic range or memory, like a SAR DAC or something.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 22, 2018, 04:58:50 am
content: Quote from: coppercone2 on December 21, 2018, 01:34:14 pmActually probably can just mimic a common failure mode - solder a few down and then flex the board a bunch. Could also try thermal shocking by soldering one end and then putting a drop of water on the other or something (though, definitely with eye protection).Don't know enough about the physics to make any accuracy requirement estimate, but you can try enhanced resolution modes on the scope as a baseline, and then trace averaging for a bit more. Even for impulse response, if you measure hundreds impulses or more you should be able to get lower effective noise. Maybe you'll still need some bits to see the information you want beyond that, but once you start seeing an interesting signal you can look into higher resolution converters with that kind of bandwidth (something like the converters in an SA, most modern ones should be able to do realtime/time domain analysis in the 10s of MHz range).

author: coppercone2
author_rank: Super Contributor
timestamp: December 22, 2018, 05:01:07 am
content: do you think frequency of oscllation would change the crack profile?I thought to make a PCB of particular mechanical lenght with the part in a particular place and use some kind of motor to jiggle the PCB. Like a rotational to linear converter.

author: rhb
author_rank: Super Contributor
timestamp: December 22, 2018, 02:28:55 pm
content: I'd forgotten about lasers. You might be able to get the BW required using a laser pulse as the source and an interferometer as the receiver. But the resulting system would be *very* complex.There is no escape from the wavelength vs resolution problem. That's the fundamentals of the wave equation at work.

author: rhb
author_rank: Super Contributor
timestamp: December 23, 2018, 04:09:31 pm
content: This is *really* cool. I am astonished at the experimental result. Setup is a 5 nS pulse at 10 MHz repetition rate from my 33622A and my MSO2204EA.The first image is the SG connected to the scope via a 50 ohm thru. Visually it looks perfectly Gaussian and zero phase. DS0123.PNGThe next image is the SG pulse fed to the DSO with the FFT turned on. We see a classic comb spike series every 10 MHz from DC to Nyquist at 500 MHz and a clear picture of the antialias filter amplitude response. DS0125.PNGThe 3rd image is with the SG and the scope connected to the bare xtal. It has now has a minimum phase very broadband filter applied which results in the asymmetric waveform. Bode wrote the classic paper on this. It's important to note that the ringing I expected at the fundamental of the xtal is not seen. This was a real surprise for me and suggests that a 10 cent xtal may work as a piezo transducer to very high frequencies. This is the shortest pulse I can produce. I now have an excuse to buy one of Leo's 100 pS long pulse generators DS0116.PNGI then attached a 0.55 mm thick piece of plastic between two xtals with super glue. In this instance the source and receiver are the same xtal. In accordance with theory, we see ringing as the pulse travels through the plastic disk and xtal, hits the air-xtal interface and is reflected with a negative reflection coefficient. It then travels through the disk until it hits the opposite air-xtal interface and is reflected again. DS0130.PNGThe last image is the direct arrival through the disk detected by the 2nd xtal. All the other stuff is reflection off the air-quartz interface at the back side of the xtals. DS0128.PNGThe single xtal reflection response suggests that a simple probe that one pressed against a part might actually work.I'll repeat the tests later with my LeCroy, but I'm beginning to think that coppercone's idea might actually work. after all.

author: coppercone2
author_rank: Super Contributor
timestamp: December 23, 2018, 04:54:07 pm
content: hmm I have a 50KHz 70ps wave generator (old tektronix unit).Too bad I am on vacation or I would experiment with this. I also have a nice VNA meant for categorizing crystals as a matter of fact. what you did is clever. I would like to see this work.I wonder how you can couple tweezers to a part. I wonder if a lossy deformable material would work better despite the attenuation then a hokey contact between hard tweezers and a hard part.god the box of crystals I got off ebay a long time ago has been bugging me, I literally used 1 part from it. one of those purchases which made me question keeping components at all. salvation at last?also may be of some interest about crystals

author: coppercone2
author_rank: Super Contributor
timestamp: December 23, 2018, 05:14:53 pm
content: hopefully i can link the ode to joy within 2 days?

author: rhb
author_rank: Super Contributor
timestamp: December 23, 2018, 05:52:28 pm
content: I don't think tweezers are needed. I think a pencil like probe that one pressed down on top of the part is the most attractive option. The resonance frequency of a cracked part will be higher than a part which is not cracked. There's really not a lot more information to be gained from the transmission response. In fact, it was proved over 40 years ago that given the transmission response of a stack of layers you could derive the reflection response and vice versa.However, this would only apply to cracks parallel to the PCB plane. But it should make a very good way to locate cracked SMD solder joints.Here's a photo of the DUT used. It's just two 40 MHz 3rd overtone xtals with the cans removed and a piece of thin plastic glued between them. I bought 100 for $10 long ago to use to build xtal filters. The minimum phase response of the bare xtal assures me that the ringing with a single sensor is a measure of the travel time thickness of the sandwich.I made a similar plot before I glued the 2nd sensor on, but failed to transfer it to the PC. I find it interesting that a 1 Meg load on the 2nd xtal modifies the response of the first xtal.

author: coppercone2
author_rank: Super Contributor
timestamp: December 23, 2018, 06:00:49 pm
content: I am actually not sure in which direction cracks in SMD parts form, I thought it was perpendicular to the PCB but I am sure both types are possible.

author: rhb
author_rank: Super Contributor
timestamp: December 24, 2018, 12:06:28 am
content: I'd expect mulitlayer capacitors to crack parallel to the layers. So it would depend upon how they were mounted.I've got an ~1/4" length of 3/8" aluminum rod with an xtal glued to it with hotmelt. I can just barely make out the reflection around 137 nS and I've got a lot of ringing in the hotmelt layer. A friend who spent his career doing this sort of stuff in a major oil company lab suggested I try honey to attach the xtal to the sample.The signal is very faint as I can only apply 5 V drive, but at the moment I'm DC coupled, so I may be able to double that to 10 V.It's still a long way from what I've done so far to having a usable tool. But just being able to check for cracked solder joints would be very useful. But I've got to figure out a way to reinforce the xtal without loading it too much. The xtal is the thickness of 2 sheets of copy paper and very brittle. The need to make electrical connections to both side of the xtal further complicates things.I think the next test will be to sweep the xtal from 1 Hz to 120 MHz and see how flat the response is. That would solve the limited power input, but if you have to sweep for an hour it won't be much use.In any case, the DSP code to make a tool rather than a lab demo will require significant effort. I'm very familiar with it, but it's very fiddly.I'm going to look for some lower frequency xtals as they will be thicker.I've always wanted to do this with rocks, so I'm having a blast even if this doesn't work out. I never had a chance to actually do anything hands on. I just got sheets of paper and did a bunch of calculations. Just not as much fun.Have a Merry Christmas.

author: coppercone2
author_rank: Super Contributor
timestamp: December 24, 2018, 12:40:55 am
content: a crazy option is to maybe use liquid metal that is adhered to something by surface tension to make a low mechanical resistance connection to the crystal. Like two droplets of liquid metal that are upside down that touch the crystal legs.Otherwise an option might be to take incredibly fine wire (say from mutli strand silicone wire that is very fine) and make a weave (I noticed solder braid is very nimble). Not sure what weave structure would work but people make weird bracelets that are pretty nimble. you could assemble it with fine tweezers under magnification but it would be a japanese effort. I don't know what the finest gauge wire they sell on spools is but I have a hunch crazy high strand count conductor would be finer. You can split a wire with a exacto blade or a special jig to remove the insulation and access the fine strands.glue dots, silicone putty (silly putty), double sided tape, pitch, tar, fun tack (they sell it at home depot), self bonding tape, liquid electrical tape (doubtful), all come to mind as a inbetween to honey and hot glue.I am also wondering about if you made a little gasket between the crystal and the tweezers, filled it with honey or whatever, then used some kind of rubberish zip-tie to hold it in place (they sell weird stuff like this from panduit to act as 'softer' couplers.Also I have seen that gaskets are actually bonded with cyanoacrylate (if you wan to make a custom replacement gasket with a gasket kit). This might also mean you can make a custom sized rubber band by cutting an existing one precisely and using super glue to bond it.and instead of honey there are also dielectric lubricant gels like the ones used for crimps but they might actually be worse for circuits if you follow nasa guidelines about glass formation on arcing relays as a result of silicone contamination. But in all seriousness honey could result in a life-form problem of some kind ranging from microbial to rat or maybe even bear sized if it warms up and smells nice.

author: rhb
author_rank: Super Contributor
timestamp: December 24, 2018, 01:07:38 am
content: Dried honey is a water soluble glue that will form a very thin film. The operative word is "thin". It's also easy to handle which super glue is not.Glue dots are a nightmare. Double sided tape might work, but it's still thicker than a film of honey. The requirement is that the layer be extremely thin so that the resonance in the layer is very high. If that is not the case, most of the energy is trapped in that layer.

author: coppercone2
author_rank: Super Contributor
timestamp: December 24, 2018, 01:14:11 am
content: oh so its not really a big gap filler, you are not trying to get a wider contact area, just a better contact area (in the edge)? I imagined a big glob.yea the only other thing that comes to mind right now is cooling down the tweezers with a peltier to increase the viscosity of something inorganic

author: rhb
author_rank: Super Contributor
timestamp: December 24, 2018, 11:53:45 am
content: The ideal glue would have a density of 2.65 grams/cc and be water thin. I'm going to look for a source of sodium silicate.A single transducer as both source and receiver (e.g. an old style medical ultrasound) is the only way I can see to make this work. Otherwise you have to solve for the response of the tweezers and correct for it. That's a major PhD dissertation project over the course of several years.But it *might* be possible to get distinct reflections from the chip to board interface and the back of the board. A strong reflection before the back of board reflection would indicate cracking. But there is the problem of the reflection from the backside of the transducer support.Last night I hit on the idea of a piece of thin sheet ( e.g. 0.040 aluminum or plastic) supported by a spring.The requirement is that we get the reflections from the front and back of the xtal to arrive at different times. If we can't do that, then it turns into another PhD project.This whole thread is completely insane. But I'm having a lot of fun playing so I'll continue until we succeed or it's no longer fun.We are fighting very basic physics, so I expect we will lose. But I never expected the clean pulse response I got from the bare xtal.Another experiment that I just thought of is to place two xtals as close together as possible, but not touching and examine that response. The xtal may be operating in shear mode in which case there will be no response from the receiver. That changes the physics a good bit.

author: coppercone2
author_rank: Super Contributor
timestamp: December 24, 2018, 01:06:53 pm
content: with the tweezers and reflection, can you make lopsided tweezers where one portion is really massive compared to the other one, so it acts like a anvil? Maybe dissimilar metals (use a dense steel for the anvil and a aluminum for the transducer or w/e? Just so you can do the measurement through the component in the direction where cracks are likely to form.Sodium Silicate is cheap, I use it for making sand molds in lead casting that are hardened with carbon dioxide.

author: rhb
author_rank: Super Contributor
timestamp: December 24, 2018, 01:51:31 pm
content: If the transducer is attached to a large mass it won't vibrate. That's the first order problem that needs to be solved.

author: coppercone2
author_rank: Super Contributor
timestamp: December 24, 2018, 02:26:36 pm
content: no I mean just do a reflection test but put a backer on the part so it mimics the PCB board.

author: chris_leyson
author_rank: Super Contributor
timestamp: December 24, 2018, 02:43:09 pm
content: For crack detection you're going want to use pusled ultrasound to detect the distance to a crack or boundary and in some ways it's not too dissimilar to time domain reflectometry. You transmit a short burst of ultrasound into to device under test and then use the ultrasound transducer as a receiver and measure the time taken for the signal to return, if you know the propagation velocity in the material you can work out the distance to the fault or boundary. Given that the DUT is going to be small and the propagation velocity is quite high you will need to operate at some tens of MHz. I've seen 20MHz transducers used for medical Doppler at very short distances, just under the skin and 20MHz is probably the upper limit for medical ultrasound although I have seen 40MHz transducers.There are a few companies that sell bare unmounted PZT, lead zinc titanate, transducers with metalized surfaces. Mounting them is a problem as you have to make electrical contact with both surfaces and for larger low frequency transducers used in medical applications you can get away with soldering small, say 38AWG, wire onto both sides. At 20MHz or 40MHz the disc transducers are much smaller and become difficult to mount and attach electrodes to. Small high frequency transducers are rather speciallized and expensive and not something I would contemplate building at home. These guys have a good range of PZT transducers, mostly low frequency though.https://www.steminc.com/Maybe send them an email, you never know they might have something suitable.

author: rhb
author_rank: Super Contributor
timestamp: December 24, 2018, 03:40:17 pm
content: I just made a test of two xtals 5 mm apart immersed in cooking oil. I learned two things from this:the EM coupling is very strongthe SMPS noise from the Instek MSO2204EA is larger than any signal that might be present.This and the strong 10 nS delay transmission mode signal for two xtals glued to a 0.55 mm plastic disk suggest that the xtals are operating in shear mode. That's not a viable mode for this application.So I'm afraid that's the end of the experiments with the quartz crystals.I whole heartedly agree with chris_leyson's comments. I had no idea they made PZTs that extended up to even 20 MHz., much less 40 MHz. But I don't want to ask the price. I know from a friend's work building a one off lab instrument for measuring the propagation velocities in rock cores that devices made for the purpose are much too expensive to play with.The mounting problem is a major obstacle. I may pick up some cheap small PZTs and test them. But the EM coupling is a major problem. I should have recognized that early on, but I was so amazed at getting a clean minimum phase under 10 nanosecond impulse response I wasn't thinking very carefully.Edit: Added a group photo of all the test specimens and the oil bath.

author: coppercone2
author_rank: Super Contributor
timestamp: December 24, 2018, 08:01:37 pm
content: I am guessing the shield is going to be a mechanical problem to try to build? Also not sure how much I try the power system of a instek unit. are you running them with coax or twisted pair? I assume its mostly the capacitance of the plates though right?and too weak to couple over something like a ceramic rod I am guessing..

author: rhb
author_rank: Super Contributor
timestamp: December 24, 2018, 08:54:24 pm
content: The dominant signal is capacitive as there is no visible delay. In oil a compressional wave should show up 1-4 microsecond after the pulse. Water is ~1500 m/S and the plates are 5 mm apart.The problem with the Instek is there is *no* shielding around the SMPS.What I really need is about 1" of 1/4" plastic rod so that the receiver arrival is well separated from the initial pulse. I'm sure I've got something suitable, but can't think of where to look. It as to be something I can glue to. When I find something I'll uncan a couple more xtals just to measure the shear velocity.The major downside to being in my line of work is that it is impossible to get access to data unless you are working for an oil company. Which why my interest in being able to collect data myself.Your question just prodded me to try some experiments. Previously I did not have the test equipment. The 33622A was expensive even used, but it is *really* nice. It made setting up to test this very easy.

author: coppercone2
author_rank: Super Contributor
timestamp: December 25, 2018, 06:38:32 am
content: i only have a AWG2020 that works in this region, and some wavetek 50MHz AWG and 50MHz gigantic pulse generator with decent power specs. awg2040 would go higher and those look to be built decently but the PSU is not in a shield can either IIRC. 33622A looks real nice, but its also a car payment. I also think that SRS makes some kind of AWG that has a built in AA filter (the keysight 33622A spec sheet says most DDS don't have one). I actually got those function generators in the VHF range but I got bored with the VHF band due to lack of interesting applications, the only thing I wanted to do in that region is build the active circulator with fast op-amps.the awg2020 is broken until I figure out which capacitors go where with a power supply schematic because I messed up during the repair documentation processa nylon screw sounds like a candidate for a rod. you can also maybe widdle down one of those things that might be lying around for screwing a painting into a wall the expansion collet. or make a rod out of those auger things that also hold stuff on sheetrock, they are very stiff.

author: rhb
author_rank: Super Contributor
timestamp: December 25, 2018, 01:22:22 pm
content: Quote from: coppercone2 on December 25, 2018, 06:38:32 amActually more than the cash price of any of my cars except for my 1993 Toyota pickup which is the only new vehicle I bought for myself.I'd had some doubts about getting that, but I was fed up with the F***Tech FY6600. When I got that beautiful 5 nS pulse it made it all worth while. I plan to get one of Leo Bodnar's pulsers modified to emit a 90-500 pS pulses at 10 million per second. I've got to decide what pulse width I want. I'd like 100 pS, but that would be rather attenuated by the limited BW of my gear. So I may have to settle for 200 or 250 pS.Nylon is going to be lossy, particularly shear mode propagation so I'm looking for polystyrene. I know I have the plastic wand for adjusting window blinds somewhere. I threw the blind away, but the plastic rod looked useful. But a lifetime of that and it gets hard to find things.Keep in mind that it will take an amplifier capable of generating 10V or more peak out up to several GHz to make this crazy idea of yours work. So you might want to start looking for a suitable MMIC and thinking about how to build the thing. Board layout will be absolutely critical.The concept may be simple, but actually making it work is wickedly difficult. But you've given me an excuse to buy one of Leo's new toys.

author: coppercone2
author_rank: Super Contributor
timestamp: December 25, 2018, 06:19:18 pm
content: i am not sure what material it is, but if you melt a cup down in acetone you can make a putty that will solidify and be pretty brittle. its some kind of styrenewith gloves you can kinda mold it too, i used to play with that when I was small

author: rhb
author_rank: Super Contributor
timestamp: December 25, 2018, 10:10:21 pm
content: It's called polystyrene.

author: coppercone2
author_rank: Super Contributor
timestamp: December 26, 2018, 01:05:59 am
content: i don't think the grade you get from that is the same as a real polystyrene part, its pretty brittle. I thought about messing with it by reducing the pressure a bit but not too much or letting it evaporate in a dish slowly and dehydrating it a few times so it can maybe achieve a higher density but I never bothered doing serious experiments on it. and it might have a different composition and additives then a mechanical part because its from foam.i don't want people getting a false impression that you can get great results doing that. its liquid string cheese

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 12:39:08 pm
content: https://www.eevblog.com/forum/chat/sydney-tower-colllapse-fears/?topicseenimagine a cheapie could check for structural problems or shifts, may be interesting even if you dont care about capacitors