Random vibration analysis of PCB
Random vibration analysis of PCB
(OP)
Hi,
This is regarding the random vibration analysis of PCB.
One of our group company is involved in the design and maufacture of PCB board for electronic circuits -UPS systems.
In this regard, they are looking forward to evaluate the vibration, shock and thermal robustness of the PCB.
Our team being assigned in this vibration and shock test of the PCB board, both analytically (using FE) and then validation using testing.
In this regard, I have gone through this link
"ht tp://elect ronics-coo ling.com/h tml/2005_a ugust_tech brief.html"
In this link (Vibration analysis of electronic equipment), they quoted the transmissibility as
Q = C (fn)^1/2
How they arrived out this relationship.
Where is the effect of excitation frequency and damping in this equation? or they used any empirical relations?
Then in the same article, it was quoted as
"Once an approximation of deflection is made, it should be checked against the design limits. In order to reduce deflection, stiffness of the board has to increase. This is usually done via stiffeners, additional anchor points, snubbers, and other mechanical means. In order to reduce stresses on PCBs or various devices on them the general guideline is to "decouple" hardware by one octave, i.e., 20, 40, 80, 160, and so on. For instance, the relationship between the chassis to board to a heat sink/bracket should follow the above multiplier. This helps mitigate any potential coupling between various constituents of the box."
I could not understand "In order to reduce stresses on PCBs or various devices on them the general guideline is to "decouple" hardware by one octave".
Can any one help in clarifying the above statement?
Looking foward for your help.
Regards,
Logesh.E
This is regarding the random vibration analysis of PCB.
One of our group company is involved in the design and maufacture of PCB board for electronic circuits -UPS systems.
In this regard, they are looking forward to evaluate the vibration, shock and thermal robustness of the PCB.
Our team being assigned in this vibration and shock test of the PCB board, both analytically (using FE) and then validation using testing.
In this regard, I have gone through this link
"ht
In this link (Vibration analysis of electronic equipment), they quoted the transmissibility as
Q = C (fn)^1/2
How they arrived out this relationship.
Where is the effect of excitation frequency and damping in this equation? or they used any empirical relations?
Then in the same article, it was quoted as
"Once an approximation of deflection is made, it should be checked against the design limits. In order to reduce deflection, stiffness of the board has to increase. This is usually done via stiffeners, additional anchor points, snubbers, and other mechanical means. In order to reduce stresses on PCBs or various devices on them the general guideline is to "decouple" hardware by one octave, i.e., 20, 40, 80, 160, and so on. For instance, the relationship between the chassis to board to a heat sink/bracket should follow the above multiplier. This helps mitigate any potential coupling between various constituents of the box."
I could not understand "In order to reduce stresses on PCBs or various devices on them the general guideline is to "decouple" hardware by one octave".
Can any one help in clarifying the above statement?
Looking foward for your help.
Regards,
Logesh.E





RE: Random vibration analysis of PCB
"It has been shown empirically that the transmissibility, Q, of a printed circuit board is proportional to square root of the natural frequency"
So it is what it is.
Decoupling means that you want the resonances of the components should not overlap. This spreads the energy out over different frequencies. Otherwise, if all your components and board resonated at the same frequency, the board would literally tear itself apart.
TTFN
RE: Random vibration analysis of PCB
Thanks.
I missed that completely (Empirical).
Regarding decoupling, I have a doubt.
I assume that, modal analysis of PCB board, has to carried out with all the components mounted on it as a system. In this scenario,How to know the component wise resonance,which correpond to natural frequencies of the individual components? or do you mean that there has to be impedance mis-match between the components within the system?
Pl. correct me, If my statment is wrong?
Looking forward for your help.
Regards,
Logesh.E
RE: Random vibration analysis of PCB
TTFN
RE: Random vibration analysis of PCB
TTFN
RE: Random vibration analysis of PCB
Thanks again.
Regards,
Logesh.E
RE: Random vibration analysis of PCB
FE analysis of electronics is quite different from FE analysis of mechanics because FE modelling of the componenets most likely to fail is rather complicated. The following approach work:
- Test the natural frequencies of the PCB (this of course requires that the PCB is already laid out and manufactured). This is necessary, because it is almost impossible to estimate dynamic properties of a PCB with componenets. (Mass & stiffness distribution)
- Tune your FE model of the PCB as tested. This may require FE-modelling of large mounted components.
- Include your tuned PCB model into the assembly. Your PCB is not verified until the whole assembly where the PCB is mounted is included.
- Design your PCB support (with mass of PCB included) according to the octave rule (as explained by Dave Steinberg in one of his books)
- Verify your PCB for excessive curvatures
This is a design approach that works.
RE: Random vibration analysis of PCB
RE: Random vibration analysis of PCB
Available from:
h
This text gives empirical formulas for the allowable circuit board relative displacement for given parameters. The formulas can also be used as design guidelines. The goal is to avoid fatigue failures of piece part leads and solder joints.
Tom Irvine
www.vibrationdata.com
RE: Random vibration analysis of PCB
Steinberg came up as a design engineer and is now an honorary professor at at least one major university (but he has no PhD). He's retired now but might still be doing some training. A great down-to-earth guy with gobs of knowledge! His books are pricey but worth the money because it's possible to solve practical problems without too much trouble.
Tunalover