Well to me Peter is dosent look like pressure applied to the chip as a consideration , but the amount of pressure applied.Looking at it from a strictly physics point of view you have a light weight object attached to a heavier object (H/S) from 1 point (standard config), the only thing that is damping movement (vibrations) of the chip is the components attached to the chip (P2P only) by providing mass at the end of a cantilevered component (chip).The bar attachment would provide more contact area of the chip/H/S interface (heat transfer also) and with the greater mass of the H/S having energy transfered to the H/S there would be less energy being applied to the chip.The bar could be actually tuned (as far as vibration transfer) by the amount of torque applied.
ron
ron
analog_sa said:
I have my caps stripped of the heat shrink cover and seperated/joined by silicone, and it helps dampen their microphonic properties just by lowering their resonance, I guess. I know that cheesy heat sings that ring also are very audible, and a denser wood top also helps dampen any vibrations that might find their way to heat sinks or big PSU caps, so I do think material does have an effect.
And
cooler looking cases DO sound better.
Re: Don't kill me
Hello Chris,
According to your logic it seems beneficial to dampen the surface rather than just try to dampen the unit itself.
Thanks
Chris
chris ma said:IMHO/imagination, mechanically speaking, sometimes when the case of a unit is very firmly secured on a vibrating surface, the components inside the unit may vibrates more than the surface. But if the unit is just firmly secured not loose, the components inside may vibrates equal to or less than the surface, relativity motion?
Of course I have no proof of any of the above, some how it just seem logical to me
Chris
Hello Chris,
According to your logic it seems beneficial to dampen the surface rather than just try to dampen the unit itself.
Thanks
Chris
Sorry, this is an added note.
This is all dependant on 2 things, the torque applied and the mass of the H/S. It would appear logical that if the H/S had enough mass and was isolated from the cab it would be a stand alone energy damping confg., if the H/S had a lesser mass then a method of transfering energy away from the assy would have to be implimented.
ron
(love dem big words)LOL
This is all dependant on 2 things, the torque applied and the mass of the H/S. It would appear logical that if the H/S had enough mass and was isolated from the cab it would be a stand alone energy damping confg., if the H/S had a lesser mass then a method of transfering energy away from the assy would have to be implimented.
ron
(love dem big words)LOL
The kind of material used to secure the chip to the HS may be more important than the vibration issues that sound very shady and quite counter intuitive.
Bolting down the chip using a big Al bar which may introduce unwanted parasitics if the heatsinks happens to be grounded. Has anyone tried using a piece of delrin or some other non conductive/non magnetic material to fasten the chip?
Bolting down the chip using a big Al bar which may introduce unwanted parasitics if the heatsinks happens to be grounded. Has anyone tried using a piece of delrin or some other non conductive/non magnetic material to fasten the chip?
I was thinkng about my next design as one of those gold plated buss bars used in auto sound.The one i was looking at weighs 1.5 lbs and is , if i remember right,1.1"x.75"x3.xx" length.This would give enough surface area(chip mounting) and if isolated from the cab by nylon screws (or other means) would provide enough mass for method #1.It would also be easy to drill several .75" thru holes to provide for augmented convection cooling.The bar would be mounted in the lower area of the cab and isolated with the legs of the chip going up.(unless someone thinks that gravity will affect electron flow )LOL.OK OK now i am getting silly, need more coffee.
ron
ron
Excellant idea grataxu.The transfer of energy would be less prone to harmonics if the hold down bar was low mass, and thinking about it the load would have to be distributed across the face evenly so the torque screws would have to be at a min. close to either side of the chip and the width of the bar should be at least as wide (Y direction) as the chip face for even load distribution.Maybe 4 torque screws/chip.
ron
Ok but the torque applied,if excessive, would bow the hold down bar causing less surface area at the interface, so it would be an action of tuning , so to speak,for the proper torque applied.I would suggest even still using the mounting hole in the chip using nylon screws or something of the like.
ron
ron
Ok but the torque applied,if excessive, would bow the hold down bar causing less surface area at the interface, so it would be an action of tuning , so to speak,for the proper torque applied.I would suggest even still using the mounting hole in the chip using nylon screws or something of the like.
ron
Still thinking aloud!
OK the way i see it now is a rigid hold down bar ie: alum, copper ect.with a delrin strip bonded to it on the face side that will interface with the chip face.This eliminates several problems but for load distribution it will still have to be wide enough to cover the chip face and the torque screws will have to be at 4 places(each chip) as close to the chip as possible.
ron
OK the way i see it now is a rigid hold down bar ie: alum, copper ect.with a delrin strip bonded to it on the face side that will interface with the chip face.This eliminates several problems but for load distribution it will still have to be wide enough to cover the chip face and the torque screws will have to be at 4 places(each chip) as close to the chip as possible.
ron
What about Piezoresistive Sensors
I am curious if industrial solid state Piezoresistive pressure sensors have anything in common with case microphonics and the effects of vibrations on semiconductors.
Solid state pezoelectric microphones turn mechanical vibrations into electrical signals. Is it not possible that one of the multiple semiconductor junctions may act in this fashion in a small way? Can you rule it out?
Just food for thought...I'm not totally convinced yet and I guess I would need quantitative information to help rule it out.
I am curious if industrial solid state Piezoresistive pressure sensors have anything in common with case microphonics and the effects of vibrations on semiconductors.
Solid state pezoelectric microphones turn mechanical vibrations into electrical signals. Is it not possible that one of the multiple semiconductor junctions may act in this fashion in a small way? Can you rule it out?
Just food for thought...I'm not totally convinced yet and I guess I would need quantitative information to help rule it out.
hi,
monocrystalline Si is a "good" piezo material... you can easily (well easier said than done) create piezoelectric actuators and piezoelectric and piezoresistive sensors with it.
BUT:
the power transistor/ic die is soldered to the metal tab for good heat transfer. that means the die practically doesn't bend => no piezo effects. It may bend a little bit because of different thermal expansion coefficients of Si, solder, and tab metal..
so i think the piezo effects in Si don't play a significant role here.
the whole chip is subject to the same vibrations => no effect.
re: clamping the device using the plastic body.. if it isn't overtightened, the package won't be damaged.
I don't think you can "tune" it this way, because the chip is only soldered to the metal tab, it isn't connected to the plastic covering it.
re: the creating a cap discussion...
i don't think it is significant. the chip is not attached to the plastic. a metal clamping bar will create a capacitor between heatsink and the package metal tab with the package plastic as dielectric. I bet this capacitance will be FAR smaller than "tab / iso pad / heatsink" that is there anyway.
of course you could argue that a capacitance between the leadout wires (which have to go through the plastic package) and the clamping bar will be created, but these C already exist as series connection of Wire-Tab and Tab-HS. they will just get a bit larger. Calculate how small these capacitances are! fF probably!
several people have reported better heat transfer with devices clamped this way.
i have clamped IRFP240 power MOSFETs in this way in my old Aleph-3 project. It works flawlessly, very good heat transfer, with Al2O3 pads. the clamping bar goes over the whole package in my implementation and is made from 4mm thick alu.
YMMV!
k
monocrystalline Si is a "good" piezo material... you can easily (well easier said than done) create piezoelectric actuators and piezoelectric and piezoresistive sensors with it.
BUT:
the power transistor/ic die is soldered to the metal tab for good heat transfer. that means the die practically doesn't bend => no piezo effects. It may bend a little bit because of different thermal expansion coefficients of Si, solder, and tab metal..
so i think the piezo effects in Si don't play a significant role here.
the whole chip is subject to the same vibrations => no effect.
re: clamping the device using the plastic body.. if it isn't overtightened, the package won't be damaged.
I don't think you can "tune" it this way, because the chip is only soldered to the metal tab, it isn't connected to the plastic covering it.
re: the creating a cap discussion...
i don't think it is significant. the chip is not attached to the plastic. a metal clamping bar will create a capacitor between heatsink and the package metal tab with the package plastic as dielectric. I bet this capacitance will be FAR smaller than "tab / iso pad / heatsink" that is there anyway.
of course you could argue that a capacitance between the leadout wires (which have to go through the plastic package) and the clamping bar will be created, but these C already exist as series connection of Wire-Tab and Tab-HS. they will just get a bit larger. Calculate how small these capacitances are! fF probably!
several people have reported better heat transfer with devices clamped this way.
i have clamped IRFP240 power MOSFETs in this way in my old Aleph-3 project. It works flawlessly, very good heat transfer, with Al2O3 pads. the clamping bar goes over the whole package in my implementation and is made from 4mm thick alu.
YMMV!
k
I have worked for many yeas as an ultrasonic inspector in industry.In the old days they used lithium sulfate as the piezo to emit and recieve ultrasonic waves on the order of 500 Khz to 20 Mhz(today its much more advanced materials).Any polerized (and some non polerized) semiconductor will either change values or emit tiny voltages when mechanical stress are induced.
Another major test method is called a strain gage.Its a semiconductor that is actually glued onto a mechanical test object and by loading the object in differet directions and with different loads the reistance changes and measured and the load paths are calculated.
Ok back to what we were discussing, i see no reason that wood would not work as a hold down for the chip. I see a strip of .5" hard wood as being an application.
ron
Another major test method is called a strain gage.Its a semiconductor that is actually glued onto a mechanical test object and by loading the object in differet directions and with different loads the reistance changes and measured and the load paths are calculated.
Ok back to what we were discussing, i see no reason that wood would not work as a hold down for the chip. I see a strip of .5" hard wood as being an application.
ron
Yes, but the torque is loading the chip metal surface to the H/S.Its transfering vibrations by the amount of loading. If you load a light object to a heavy object the two (at some point) become a unit of (almost) one.Think of it as an adjustable shock adsorber(IMHO koni makes the best) as the loading gets greater the suspesion gets closer to becoming a single unit with the car.
ron
ron
OT: Piezopolymer
No.
In order to get any significant piezo effect from a polymer, you need the right kind of molecular structure in terms of polar moments and freedom to align. The polymer polyvinylidene difluoride (PVDF) in a linear form fits that bill nicely. It's the same polymer normally used to insulate wire wrap. And you'll note that wire wrap wire is not microphonic.
To make PVDF show piezoelectric properties, it has to go through a process known as "poling." The polymer is extruded into thin sheets, the sheets are heated to near the softening point, where the linear molecules can crank around about the long axis pretty freely. A high voltage gradient is impressed across the polymer to get the fluoride parts (negative) pointed in one direction and the vinyl parts (positive) pointed in the other. The polymer film is then cooled rather rapidly to "freeze" that alignment. At that point, it can be metallized or have contacts formed in some other way.
Other solid state sensors are made from highly crystalline and chemically controlled silicon. It has to be "machined" in an extremely precise way, with some pretty exotic equipment.
So, unless the case was made of a very special material and poled, it's unlikely to have any significant piezoelectric effect.
No.
In order to get any significant piezo effect from a polymer, you need the right kind of molecular structure in terms of polar moments and freedom to align. The polymer polyvinylidene difluoride (PVDF) in a linear form fits that bill nicely. It's the same polymer normally used to insulate wire wrap. And you'll note that wire wrap wire is not microphonic.
To make PVDF show piezoelectric properties, it has to go through a process known as "poling." The polymer is extruded into thin sheets, the sheets are heated to near the softening point, where the linear molecules can crank around about the long axis pretty freely. A high voltage gradient is impressed across the polymer to get the fluoride parts (negative) pointed in one direction and the vinyl parts (positive) pointed in the other. The polymer film is then cooled rather rapidly to "freeze" that alignment. At that point, it can be metallized or have contacts formed in some other way.
Other solid state sensors are made from highly crystalline and chemically controlled silicon. It has to be "machined" in an extremely precise way, with some pretty exotic equipment.
So, unless the case was made of a very special material and poled, it's unlikely to have any significant piezoelectric effect.
Konnichiwa,
I take it, given the way you present your statement that you evaluated scientifically the behaviour of Chips and concluded that mechanical stresses do not change the behaviour of a chip.
Or are you actually just presenting an assumption based on what you think things should be, if they behaved like in an engineering textebook, as opposed to reality?
Hmmm. So, if in reality, under controlled conditions I observe microphonic reactions in Capacitors and monolithic IC's I should read an Engineering Textbook to convince me my empirical results are wrong?
So an Engineering textbook is now the Yardstick to which the reality has to bend itself?
I notice with you a position that is typhical for many (Electronic) Engineers and shows a delporable lack of basic logical and analytical facilities.
You demand an explanation that agrees with your textbooks? There is non, as the Textbooks contain drastic and glaring simplifications and omissions together with a concentration on what the author thought "essential" and "didactic".
I don't really know what to say to you... More empirical research in reality perhaps?
Sayonara
Doovieman said:
I take it, given the way you present your statement that you evaluated scientifically the behaviour of Chips and concluded that mechanical stresses do not change the behaviour of a chip.
Or are you actually just presenting an assumption based on what you think things should be, if they behaved like in an engineering textebook, as opposed to reality?
Doovieman said:
Hmmm. So, if in reality, under controlled conditions I observe microphonic reactions in Capacitors and monolithic IC's I should read an Engineering Textbook to convince me my empirical results are wrong?
So an Engineering textbook is now the Yardstick to which the reality has to bend itself?
I notice with you a position that is typhical for many (Electronic) Engineers and shows a delporable lack of basic logical and analytical facilities.
You demand an explanation that agrees with your textbooks? There is non, as the Textbooks contain drastic and glaring simplifications and omissions together with a concentration on what the author thought "essential" and "didactic".
I don't really know what to say to you... More empirical research in reality perhaps?
Sayonara
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