Archive for May, 2022

What are the Factors Affecting the Thermal Conductivity of AlN Ceramic Substrate?

Tuesday, May 31st, 2022

The Introduction of AlN Ceramic

With hexagonal wurtzite structure and no other homomorphic isomers, AlN, aluminum nitride, is a structurally stable covalent bond compound, whose crystal structure is AlN4 tetrahedron formed by the dismutation of aluminum atom and adjacent nitrogen atom. And its space group is P63mc, belonging to hexagonal system.

The Features of AlN Ceramic

  1. High thermal conductivity, which is 5 to 10 times than that of aluminum oxide ceramic.
  2. Coefficient of thermal expansion (4.3*10-6/℃) matches the semiconductor silicon material (3.5-4.0*10-6/℃).
  3. Great mechanical properties.
  4. Excellent electrical performance, with high insulation resistance and low dielectric loss.
  5. Multi-layer wiring can be carried out to achieve high density and miniaturization of packaging.
  6. Non-toxic, conducive to environmental protection.
Ceramic PCB

Factors Impacting on the Thermal Conductivity of AlN Ceramic

At 300K, the theoretical thermal conductivity of AlN single crystal material is as high as 319 W/(m·K). But in the actual production process, its thermal conductivity will still be affected, which is often lower than the theoretical value due to the influence of various factors such as the purity and internal defects (dislocations, pores, impurities, lattice distortion) of material, grain orientation and sintering process.

Effect of Microstructure on Thermal Conductivity

The heat conduction mechanism of single crystal AlN is phonon heat transfer, hence the thermal conductivity of AlN may be mainly influenced by the scattering control of grain boundary, interface, second phase, defect, electron and phonon itself. In accordance with the solid lattice vibration theory, the relation between phonon scattering and thermal conductivity “λ” is as follows: λ= L / 3CV.

In the formula, C is the heat capacity; V represents the average velocity of phonons; and L stands for the mean free path. And it can be seen from the equation that the thermal conductivity (λ) of AlN has direct ratio with the mean free path (L), for which the larger “L” is, the higher the thermal conductivity is. From the perspective of microstructure, the scattering can be caused by the interaction between phonons and phonons, phonons and impurities, and phonons and grain boundary.  It will affect the mean free path of phonons, and thus impact on the thermal conductivity.

It can be learnt from above that the microstructure of AlN has a great influence on its thermal conductivity. Therefore, it is necessary to make AlN crystals with fewer defects and impurities in order to obtain AlN ceramics with high thermal conductivity.

Effect of Oxygen Impurities Content on Thermal Conductivity

There are studies show that AlN has a strong affinity with oxygen so that it is easy to be oxidized, leading to the formation of aluminum oxide film on its surface. Owing to the dissolution of oxygen atoms in Al2O3, the nitrogen in AlN is replaced, resulting in aluminum void and oxygen defect. In this way, it will bring about the increase phonon scattering and decrease of mean free path hence the thermal conductivity will be reduced.

Oxygen Content in AlN (wt%)Thermal Conductivity (W/m·K)
0.31130
0.24146
0.19165
0.13171
0.12185

So, it can be concluded that the types of defects in AlN lattice are related to the concentration of oxygen atoms.

  • When the oxygen concentration is lower than 0.75%, oxygen atoms evenly distributed in the AlN lattice, replacing the position of nitrogen atoms. And then the aluminum void is accompanied by it.
  • When the oxygen concentration is not less than 0.75%, the position of Al in aluminum nitride lattice will have a change. Then the aluminum void will disappear, causing octahedral defects.
  • When the oxygen concentration is higher, the lattice will produce extension defects such as polytype, inversion domain and oxygen-containing stacking fault. Moreover, based on thermodynamics, it is found that the amount of oxygen in AlN lattice is under the influence of Gibbs free energy (ΔG°). The larger the ΔG° is, the less oxygen is in the lattice, hence there will be a higher thermal conductivity.

Therefore, the thermal conductivity of aluminum nitride is seriously affected by the existence of oxygen impurities, which is a key point resulting in the decrease of thermal conductivity.

Thermal Conductivity can be Enhanced by Suitable Sintering Aids

In order to improve the thermal conductivity of AlN, the required sintering aids need to be added to lower sintering temperature and remove oxygen in lattice.

As matters stand, the addition of multiple composite sintering additives is followed with more interests. And the experiment shows that relatively dense AlN samples with less oxygen impurities and the secondary phase can be obtained by adding the composite sintering aids, Y2O3-Li2O, Y2O3-CaC2, Y2O3-CaF2, Y2O3-Dy2O3, to aluminum nitride.

In a word, selecting appropriate composite sintering additives can help to get lower sintering temperature and effectively purify the grain boundary, so as to obtain AlN with high thermal conductivity.

In case if you have any other questions about ceramic PCB or MCPCB, you are welcome to contact us via email at sales@bestpcbs.com. We are fully equipped to handle your PCB or MCPCB manufacturing requirements.

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Pros and Cons of the Ceramic PCB

Friday, May 27th, 2022

Ceramic PCB is used in various fields because of its high-quality thermal and mechanical advantages. The board’s unique features and high thermal conductivity have enabled it to be used in devices big and small. But meanwhile, it is not flawless. There are also some disadvantages.

Ceramic PCB

Pros of ceramic PCB

It is supposed that you are familiar with the features below that the ceramic PCB has.

  • Excellent thermal conductivity.
  • Good insulation.
  • High temperature resistance.
  • Great mechanical properties.
  • Compatible with CTE (Coefficient of Thermal Expansion) of components.
  • High-density assembly possible.
  • Non-toxic, conducive to environmental protection.

Cons of ceramic PCB

There are also a few disadvantages that can be found in ceramic PCB. Some of the disadvantages are stated below.

  • Cost—It has a higher cost compared to other printed circuit boards.
  • Handling—Since ceramic is fragile, it entails careful handling. As ceramic PCB is made for tight spaces, it is very small and this makes it even harder to handle.
  • Availability—It is not as widely available.

Everything has two sides. And ceramic PCB has no exception. But if considering all the advantages and disadvantages, ceramic PCB still takes the win amongst all other boards.

So, this is the end of the article about the advantages and disadvantages of the ceramic PCB. In case if you have any other questions about ceramic PCB or MCPCB, you are welcome to contact us via email at sales@bestpcbs.com. We are fully equipped to handle your PCB or MCPCB manufacturing requirements.

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Types of Vias

Friday, May 20th, 2022

What is via?

A via plays an important role in multi-layer PCBs. It is used to make an electrical connection between the layers of a multi-layer PCB. Generally speaking, every hole in the printed circuit boards can be called as via.

A via is constructed by placing copper pads on each layer of the PCB and drilling a hole through them. And the hole is plated with copper that forms electrical connection through the insulation that separates the copper layers.

PCB Vias

Types of Vias

There are three main types of vias used in PCB: through-hole via, blind via and buried via.

Through-Hole Via

Through-hole via goes right through the printed circuit board from top to bottom and can be used to connect all the layers of a PCB. It is the most common via and is easiest to construct.

Blind Via

Blind via connects the outermost layer of a PCB to the next layer. Namely, it cannot be seen on the other side of the board and is therefore called blind via.

Buried Via

Buried via is used to connect internal layers of a PCB. And it cannot be seen on the surface of the board.

Via Types

In addition, it is always better to use multiple smaller vias rather than one large via since smaller vias can reduce the inductance and also provide an additional path to the current flow in case any of the vias fail.

So, this is the end of this article. In case if you have any questions, you are welcome to contact us via email at  sales@bestpcbs.com. We are fully equipped to handle your PCB  manufacturing requirements.

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Types of Metal Bases Utilized in MCPCB

Tuesday, May 10th, 2022

What is metal core printed circuit?

Metal core printed circuit board is abbreviated as MCPCB. And namely, the core or the base material of MCPCB is a metal instead of the traditional FR4/CEM1-3.

Types of metal bases used in MCPCB

The metal cores of the thermal PCB can be aluminum, copper and steel alloys. Apart from being cheaper than copper, aluminum is known for its good heat transferring and dissipation abilities, which is the most common used. However, copper is considered to be a better performer. So, why does the aluminum become the first choice for the material of the MCPCB?

Aluminum base—The aluminum PCB offers good heat dissipation and heat transferring ability. Since they are also light in weight, the aluminum core PCBs are widely used in LED products.

Aluminum Core PCB

Copper base—The copper core board features a better performance than aluminum. But customers will usually choose the aluminum instead of copper, for it is relatively expensive. Also, compared with the aluminum, the copper is heavier and involves a tough machining process.

Copper Core PCB

Various base metals and their properties

Metal Base MaterialThermal Conductivity
(W/m-K)
Coefficient of Thermal Expansion
(µm/m-°C)
Aluminum88-25125
Copper38617

Based on the table, it can be known that although the thermal conductivity of the copper is better than that of the aluminum, its ability of thermal expansion does not perform better than the aluminum.

Therefore, there are some reasons why the aluminum is the first choice for the material of the MCPCB, including the lower cost compared to copper, light weight, excellent durability and its heat transferring capabilities.

And these are also the reasons that the MCPCB is widely used in the LED products as we mentioned in the last article.

So, this is the end of this article. In case if you have any questions, you are welcome to contact us via email at  sales@bestpcbs.com. We are fully equipped to handle your PCB or MCPCB manufacturing requirements.

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