MLCC—— is multilayer a capacitor of type pottery and porcelain, abbreviation sticks a capacitance, can cause noise howl to make an issue.

 

The howl of circuit of notebook computer power source calls give typical examples place

 

Tend to the demand of electronic equipment as people quiet, in camera of notebook computer, mobile phone, number (the respect of power source circuit of all sorts of application equipment such as DSC) , did not cause the attention “ howl that produces by capacitor vibration to call ” problem to already made the task that designs a respect before.

 

Sound results from the object is oscillatory, oscillatory frequency can be identified by person ear for the sound wave of 20Hz~20 KHz.

 

MLCC issues howl cry news, it is to say namely, MLCC produces the vibration with bigger range below voltage action (microcosmic bigger, be less than 1nm) .

 

Why is MLCC met oscillatory?

 

We should understand electrostriction of —— of a kind of natural phenomenon first.

 

Below action of outer electric field, all material can produce electrostriction of adjustable deformation —— .

 

To the ferroelectric material of certain tall dielectric constant, electrostriction effect is acuteness, call —— piezoelectric effect.

 

Piezoelectric effect includes piezoelectric effect and go against piezoelectric effect

 

 

● piece shape alone because stone capacitor is strong the character suppressing report of the pottery and porcelain of dielectric constant, in bring to bear on below the circumstance of alternating voltage, picture if the graph is shown 2 times,undertake systole.

 

● result is shown 3 times like the graph, circuit board averages day extent direction vibration. (Chip reachs the amplitude of circuit board to be left and right sides of 1pm ～ 1nm only)

 

● should the amplitude cycle of circuit board is taken in the frequency that achieves people to be able to be heard (when 20Hz ～ 20kHz) , sound can pass person ear to identify.

 

 

Mechanical to having the medium material of the character that suppress report to bring to bear on pressure, medium crystal can produce a structure to recombine a cloth, material surface is met the induction gives charge, generation voltage.

 

Go against piezoelectric effect

 

Bring to bear on to having the medium stuff of the character that suppress report voltage, produce mechanical stress, produce deformation.

 

The learning of piezoelectric effect defines:

 

“ brings to bear on on the crystal that does not have symmetrical center pressure, tension and tangential when force, happen with polarization of stress proportionate medium, in crystal at the same time two end panel will appear, negative electric charge, this one phenomenon is called piezoelectric effect. Be in conversely electric field brings to bear on on crystal and cause polarization, criterion generation and proportionate of electric field intensity are out of shape or mechanical stress, this one phenomenon is called go against piezoelectric effect. These two kinds, go against piezoelectric effect a general designation to be piezoelectric effect. ”

 

Medium of pottery and porcelain is MLCC main component, below voltage action, electrostriction is inevitable. Like electrostriction strong performance is piezoelectric effect, can produce vibration.

 

Does all MLCC metropolis howl cry?

 

Material of medium of MLCC design production pottery and porcelain basically has suitable dielectric and iron dielectric two kinds big.

 

Suitable dielectric weighs I again kind medium, basically SrZrO3, MgTiO3 waits. Deformation of suitable dielectric electrostriction is very small, below working voltage, can’t produce noise. So, suitable dielectric (I kind medium) the MLCC that material does, like NPO (COG) isotherm spends stability product, won’t produce noise howl to cry.

 

Iron dielectric weighs II again kind medium, main BaTiO3, BaSrTiO3. Iron dielectric has piezoelectric effect of intense electrostriction character — . Accordingly, iron dielectric (II kind medium) the MLCC that do, be like X7R/X5R characteristic product, apparent noise howl arises to cry in the meeting below effect of bigger strength of alternating current field.

 

As above place is shown, two end of X7R-MLCC are added change substantially after voltage, generation of BaTiO3 pottery and porcelain goes against piezoelectric effect, MLCC deformation vibration is delivered resonance happens on PCB board.

 

It is when the frequency of voltage signal inside limits of hearing of 20Hz~20kHz person ear, can hear capacitance to cry in howl.

 

Howl of what circumstance MLCC cries apparent?

 

Bigger hand in change voltage, frequency arrives in 20Hz between 20kHz, use X7R/X5R kind in high capacity MLCC, the howl with meeting apparent generation cries, wait for a circumstance like switch power source, high frequency power source.

 

 

A lot of mobile electron equipment stand by person ear, be like: Notebook computer, flat computer, smartphone, if have in electronic circuit,can listen to noise to be able to be affected use experience. Acuteness howl cries besides fulsome outside, existing possibly still the hidden trouble with dependability insufficient design. Acuteness howl makes result from acuteness vibration, oscillatory extent is decided by piezoelectric effect degree. Piezoelectric effect and electric field intensity become direct ratio, extra voltage is changeless, medium is thinner, piezoelectric effect is more powerful, howl cry news is bigger.

 

 

Rated voltage decides with medium ply character by the material of MLCC, the MLCC medium ply that acuteness howl calls to state to current job voltage place is chosen is too thin, ought to consider to choose medium thicker, the MLCC with rated taller voltage.

 

To iron report pottery and porcelain, handing in change below electric field action, return existence iron electricdomain to turn alternately the problem of inward attrition respect, hand in change field is powerful, chafe inside serious, invalidation machine rate rises. This can call the report on audio size to come out in howl.

 

 

 

The method that can hear noise what reduce MLCC capacitor generation has a lot of, all solutions can raise cost.

 

1, change capacitor type is the directest method, the capacitor that waits not to have piezoelectric effect with capacitance of suitable report pottery and porcelain, tantalum capacitance and filmy capacitance is replaced. But the problem such as space of need consideration bulk, dependability and cost.

 

2, adjust circuit, will add in MLCC to be handed in greatly change to voltage is eliminated or move its frequency give person ear to listen to feeling frequency paragraph (person ear is the most sensitive frequency is 1KHz~3KHz) .

 

3, notice pattern of plate gauge of PCB layout, PCB, the help reduces howl to make a standard.

 

4, choose the MLCC that does not have noise or low noise.

 

 

The howl that is aimed at MLCC at present makes an appearance, the design solves measure to have 3 kinds.

 

(1) add thick bottom covering layer

 

Because part of covering layer ply is,do not have inside of electrode, the BaTiO3 pottery and porcelain of this part won’t produce deformation, do not exceed ply of bottom covering layer when the soldering tin height of two end, the deformation that arises at this moment wants to PCB influence small, reduce noise effectively.

 

 

(2) structure of add metal support

 

Knot composition of a picture is as follows, it uses metallic bracket to wear MLCC chip empty.

 

 

MLCC and PCB board lie between empty, go against piezoelectric effect to produce deformation to pass amortize of metallic bracket flexibility, reduce the effect of pair of PCB board, reduce noise effectively.

 

(3) the medium data design with use weak piezoelectric effect is made

 

Pass acerbity to titanium barium (BaTiO3) the dielectric constant with farther impure particular sacrifice and temperature character, get the medium data with greatly abate piezoelectric effect, the MLCC that makes with its can reduce noise effectively.

 

Each big MLCC manufacturer, have corresponding the MLCC range of products with qualitative material of low a confusion of voices.