MLCC structure and working principle as shown in the figure below, MLCC capacitor
structure is relatively simple, by ceramic medium, the electrode metal layer and the outer electrode of three layers.
Capacitance formula of MLCC can be said as follows: C: capacitance to F (
As the unit, and MLCC capacitor value with PF, nF, and?
: insulation between electrodes dielectric constant, the unit for the ferrari/meters.
K: dielectric constant (
According to the different types of ceramic and)
A: conductive area (
Product size and printing area and different)
D: the dielectric layer thickness (
N: layer (
The stack layer)
As we all know, capacitance is the container can store electricity, its basic principle is to use two pieces of parallel to each other but not together of the metal contact, among with air or other materials as insulation, to connect two pieces of a piece of metal in the cathode of the battery, another piece in the cathode, can store charge on the metal.
Compared with common electrolytic capacitor, MLCC,
Multilayer ceramic capacitor)
Because you can make chips (
N the stack layer)
, so under the same volume of MLCC can greatly improve the capacity of a capacitor.
MLCC capacitor what is the highest temperature you get multilayer ceramic capacitor (
Generally no noe, just noticed that use temperature, type of porcelain and 2 kinds of porcelain in the use of temperature -
55 ~ + 125 degrees.
Car radial lead level of multilayer ceramic chip capacitor (
Work up to + 200 ℃ temperature range, reach class II ceramic industry in the highest temperature of hole device.
MLCC can identified in -
55 ℃ ~ + 200 ℃ temperature range work 500 hours, at + 175 ℃ temperature is no time limit.
Device has a good high temperature performance, capacity from 100 pf to 1 & mu;
F, capacitance tolerance in a strict & plusmn;
Class I and class II ceramic for MLCC using capacitance change & plusmn;
30 PPM/K C0G dielectric and - is very stable
55 ℃ ~ + 175 ℃ temperature range TCC is + / - 22%
56% of X0U dielectric.
X0U dielectric also reached the X7R specification, -
55 ℃ ~ + 125 ℃ within the scope of the capacitance change for & plusmn;
The specifications of the 15% to X9V, -
55 ℃ ~ + 200 ℃ range of capacitance change is + / - 22%
To weld on the lead frame directly, or use the plastic injection molding, capacitor using spacing 2.
5 and 5 mm.
0 mm straight leg or lead wire.
Wire diameter 0.
5 mm or 0.
6 mm, with 100% tin copper clad steel manufacturing.
Capacitor contains no lead, in line with RoHS and halogen free, manufactured refractory epoxy resin coating conforms to UL - 94 V
Another aspect is that the same material, capacity and pressure, the smaller capacity requirements of each layer medium is thinner and lead to more easily broken.
The harm of cracks is leakage, serious when cause internal short-circuit security problems, such as dislocation between the layers.
And crack have a very troublesome problem is that sometimes is hidden, when electronic equipment factory inspection may not find them, not formally exposed to the client.
So to prevent the MLCC crack is of great significance.
MLCC impacted by temperature, easy from the welding end began to crack.
In this regard, small size capacitor capacitance will be relatively better than the big size, its principle is the capacitance of thermal conductivity of the large size so fast not reached across the capacitor, so the capacitance of the ontology difference temperature difference is big, so the size is different, resulting in a stress.
This truth and pour boiled water thick glasses easier than thin glass to break.
In addition, in the process of MLCC cooling after welding, the coefficient of expansion of MLCC and PCB is different, so the produce stress, lead to crack.
To avoid this problem, the reflow soldering need good soldering temperature curve.
If it's not reflow soldering and wave soldering, so this kind of failure will increase greatly.
Should avoid to use soldering iron MLCC is manual welding process.
However, things are always not so ideal.
Soldering iron hand welding is sometimes unavoidable.
Mechanical stress is likely to lead to MLCC crack.
Because the capacitance is a rectangle (
And parallel to the PCB surface)
And short side is welding end, so nature is problematic when there by force.
Then, to consider the drainage plate stress direction.
For example as 'plate deformation in direction to the direction of the capacitance of the relationship.
In the process of production, where the PCB may generate large deformation are capacitance is not put as much as possible.
Such as PCB positioning riveting, veneer test has deformation test point mechanical contact, and so on.
Other semi-finished PCB cannot directly stacked, and so on.
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