Thin Film

Thin film describes a technology for the manufacture of a high-resolution circuit board based on a ceramic or other substrate. Due to its high degree of integration, thin film substrates form the basis of High Density Packages (HDP).

The structuring process is comparable to a traditional circuit board. The adhesive, resistor and metallization films are deposited onto the substrate surface using sputter techniques. This metallisation technology ensures an optimum adhesion of the films onto the substrate. In the subsequent photolithographic and etching processes, these films are structured according to the layout requirements. If necessary, an electroplating of the conductors is possible. Depending on the film thickness, minimum structure resolutions of 5 - 20 µm can be achieved. With the corresponding material and surface combinations, solderable and bondable surfaces can be produced. This enables the usage of the most varied of components up to a bare die assembly. The resistors produced in the thin film can be trimmed to a fixed value or according to a output signal of a hybrid circuit.

Benefits
The benefits compared to traditional printed circuit boards are the thermal and electrical properties of the substrate material as well as the fine line possibilities. The ceramic base material is very heat-conductive and as one of the chip base materials, is optimally matched to the TCE of silicon. With the above mentioned structure resolutions, considerably higher packaging and function densities can be achieved than on a conventional circuit board.

Applications
Thin film circuits meet the highest of requirements relating to reliability, lifetime and environmental compatibility. They are mainly used in the data communication units of automobile construction, telecommunications, medical and aerospace electronics. Through the reproducible electrical properties of the base substrate and the high and precise structure resolution, this technology is particularly well suited for high-frequency applications.

ECRIM thin film product capability

ECRI Microelectronics undertakes processing service of thin film products with different wafer thickness, provides various customized services, processing on a commission basis and process solutions of thin film products, has the processing capability as of thin film evaporation, sputtering, laser etching, electroplating, laser resistance trimming, wafer slicing, etc. and can provide process design schemes for thin film products.

We provide design schemes and products of various types of thin film resistance and resistance network and thin film attenuation slice , and can provide OEM processing of various kinds of ceramic film wafer and microwave wafer. We have cooperated with many microwave design units, and the frequency of manufactured microwave wafer can reach 40G Hz. Our thin film equipment and products take a leading position within the sector, the thin film production line has passed ISO9001:2002 certification, and the quality of our products satisfies the requirements of general specification for hybrid integrated circuit (MIL-PRF-38534).

Table 1 Characteristics and general applications of wafer materials for thin film

Wafer material	Dielectric constant and tolerance	Thermal expansion coefficient (ppm/oK)
Aluminum nitride (AlN)	8.85 +/- 0.35 @ 1 MHz	4.6
Aluminum oxide 99.6% (Al2O3 )	9.9 +/- 0.15 @ 1 MHz	6.5
* Other wafers can be customized separately as per customer’s demand.

Table 2 The recommended application method for thin film wafers

Frequency	Recommended thickness	Recommended dimensions of wafer (inch)
≤6 GHz	0.635mm	3 x 3
≤18 GHz	0.380mm	3 x 3
≤40 GHz	0.250mm	3 x 3
>40 GHz	0.125mm	2 x 2

Table 3 Reference values for design of common thin-film circuits

Parameter	Typical index	Limit index	Remarks
Wire width/line spacing	≥25μm	10μm
Bore size	≥500μm	250μm	Laser cutting
Line precision	3μm	2μm
Graphic margin	≥127μm	50μm
Resistance precision	≤±10%	±0.1%	Laser resistance trimming (medium resistance)
Thickness of metal layer	≥1μm	3μm

Microwave components, circuit products and miniaturization technology

Based on thin film technology, the ECRIM business division, mainly designs and develops high-performance film passive components, including microstrip filter, power divider, attenuator, microwave substrate, etc.; Active modules include L, S, C, x-band hybrid integrated low noise amplifier, mixer, oscillator, power amplifier, radio frequency channel, LC filter, harmonic generator and other products. We also customize components and components for customers. Products are widely used in wireless communication, navigation, radar and other aerospace, aviation, ground systems. It has a production line of 250,000 square inch microwave substrates and 30,000 high-end hybrid integrated circuit thin films.

Thin film technology, due to its high-precision manufacturing process and highly stable microwave characteristics, has obvious advantages over PCB and other processes in the field of radio frequency. It has fine lines, high integration and good heat dissipation. It can produce high power density circuits, especially in airborne, projectile, satellite and some high-end radio frequency systems. Its features of small size, light weight and high reliability are more prominent.

1. Thin film technology
Thin film technology products are characterized by high precision, high density, high frequency and high reliability, which are widely used in the fields of hybrid integrated circuit interconnect substrate, microwave devices, photoelectric communication, sensor, MCM, LED and so on. Typical products include microwave substrate, microstrip filter, attenuator, thin film precision resistance (network), etc.

2. The design guide

Selection of ceramic substrates
Table Selection of main parameters of ceramic substrate

Substrate parameters	Influence	Instructions
Thickness	upper frequency limit	Different frequency choose different thickness
Thickness	minimum-value aperture	50um
Dielectric constant	line width	It depends on the device performance
Surface roughness	Width of thinnest line	line width: 10um
Dissipation factor	Insertion loss	General requirements loss is less than 0.0005
Thermal conductivity	Power dissipation	Aluminum nitride/beryllium oxide for high power applications

3. Rules for thin film circuit design

Table Common reference indicators for thin film circuit design rules

project	meaning	Typical values	Special requirements
Size of substrates and chips	2 inches substrates，Usable area	46×46	48×48
	Toleranceof substrate thickness	±0.050mm	±0.020mm
	Toleranceof chips size	±0.050mm	(+0,-0.050mm)
Scribing and its accuracy	Number of available cutting	0.15mm,0.20mm	0.10mm
Scribing and its accuracy	cutting accuracy	±0.050mm
The conduction band	Minimum line width	0.018mm	0.010mm
	The smallest seam width	0.018mm	0.010mm
	A typical distance from the edge of the chip	0.050mm	0.000mm
	The line drawing of special guide should be narrower than the designed size	0.004mm
resistance	Minimum line width	0.050mm	0.008mm
	Minimum line length	0.050mm
	Minimum blank distance between the resistance edge and the conductor	0.025mm	0.000mm
	Minimum contact distance between resistance and conductor	0.050mm
	The minimum distance of the resistance film from the chip edge	0.050mm
Metal hole	The smallest aperture	50um
	The minimum distance from the edge of the hole to the edge of the figure	80um
	Minimum spacing	100um
	The minimum distance from the hole center to the edge of the chip	75um

4. Microwave cavity encapsulation technology

Microwave circuit packaging requires the following four basic functions: mechanical support and environmental protection, voltage and current path, radio frequency channel signal, control signal input and output path, and heat dissipation path.
Considering the match of the thermal expansion coefficient of the material, the packaging material should have high thermal conductivity. The basic requirements for packaging materials are high modulus of elasticity, low coefficient of thermal expansion, good finish and good planeness.
The assembly density of rf channel components is very high, resulting in high heat per unit area. Although many of the microwave devices section temperature can reach 170 ℃ above, but improper packaging material selection, heat components work can't rapid export, components inside and outside of the temperature gradient is too large, formed in the internal too hot or too hot, worsen components performance, or due to the large thermal stress damage and make the circuit structure.
ECRIM has been engaged in the research and development of metal casing for a long time. They have the largest military metal packaging shell production line in China and have rich experience in the design and manufacture of metal casing. It has the production equipment and technical ability related to the shell design, mechanical processing, glass bead preparation, air tightness sealing, brazing, electroplating, reliability test and so on, which provides reliable guarantee for the design of radio frequency channel structure. Figure 11 is a three-dimensional structure diagram of the Ku band radio frequency component structure designed for a project.
The rf channel module package is designed to adopt air tight package technology, which aims at isolating the environment, preventing pollutant erosion and making internal devices adapt to low pressure and other working conditions. At the same time, meet the electromagnetic compatibility requirements such as shielding.

5 Features of microwave products using thin film technology

5.1 High reliability
Due to the adoption of thin film technology, a large number of resistance devices in the original circuit were directly generated on the substrate, which reduced the number of welded components and improved the attenuation accuracy. At the same time, as the base plate of the channel module is directly welded to the cavity, mechanical support and environmental protection are strengthened, the performance of radio frequency grounding is greatly improved, and the reliability index of the module is comprehensively enhanced, which is suitable for mass production. Production in the national army standard production line, the quality level of G, H above.

5.2 Strong operability
Modular design is adopted, and the channel module and system level substrate can be separated for assembly test, which improves the test efficiency. Due to the effective decomposition of the test indicators, the production test can be disassembled into independent groups at the same time.

5.3 Good anti-interference
As a result of the modular design, the channel module is completely closed in a closed independent cavity, which is different from the original multi-laminar plus cavity layout. Therefore, it can better shield the crosstalk of microwave signals and power supply signals from other channels.

5.4 Small volume
After miniaturization, the area of the component is reduced by 1/3 to 1/2, and the interface form is more concise. The signal transmission between each module of the whole machine can be realized only by directly inserting and unplugging the mixed cable. Here are two examples of miniaturized products.

* Be professional in microelectronics wih 50years history.

* Technology leader,1500+ employees of 50% engineering team.

* Advance manufacturing capabilities, complete facilities in house( HTCC/LTCC/Thick Film/Thin Film/AlN/DBC/Packages/Furnaces)

* High Quality Assurance,China National hybrid microelectronics inspection center in ECRIM.

* Vertical integration capability from raw material, components, devices, modules, equipments to system integration.

* Competitive price

* Flexible Delivery, short lead time

* Fast Response.

* Customer's design available.

Capabilities

5 Features of microwave products using thin film technology