Development of a spray-coated paste for electromagnetic wave shielding
01/15/2019
Motivation
- Recently, electromagnetic noise has increased as the number of telecommunication devices increases, leading to a serious issue of malfunction.
- Conventionally, noise is shielded using a metal plate; however, the metal plate has issues to be overcome, including the weight, thickness and difficulty in processing.
- We started the development with the assumption that the current issues can be solved if we can shield any object regardless of the size and shape flexibly.
Issue
- In the environment where electromagnetic wave noise in a wide range of frequencies exists, both the internal and external noise the highly integrated semiconductor components are exposed to must be shielded component by component.
Results and Findings
- We have succeeded in developing a spray applicable conductive paste.
- Our newly developed paste provides a film with 5 to 6 µm upper thickness and 3 to 4 µm side thickness to our target of 10 µm or less film thickness.
Background of the issue
Motivation for the development
- The spread of the Internet has rapidly increased the number of telecommunications devices and sensors, allowing electromagnetic wave noise in a wide range of frequencies to be present in our surroundings.
- The internal and external noise the highly integrated semiconductor components are exposed to must be shielded component by component.
- Conventionally, the module was coated with metal, but as the trend is moving toward lighter, cheaper, and smaller modules, we saw an opportunity to develop a new conductive paste using NAMICS’ specialty technology to replace the metal material.
Overview of the development
2010 Research of printed-type paste
| Process | Cost | Film thickness | |
|---|---|---|---|
| Screen printing | Dry✓ | High× | thick× |
| Alternative technology (electroplating) | Wet× | low✓ | thin✓ |
| Sputtering (metal vapor deposition) | Dry✓ | High× | thin✓ |
We selected sputtering method despite its high cost because it enables thin coating in a dry process.
- For shielding using sputtering, stainless steel, copper, and stainless steel are deposited to make a three layers.
Higher conductivity provides more secure shielding; however, this requires thicker film and extended process time. - In order to respond to increasing high frequencies, higher shielding property is required; however, sputtering needs longer process time for a thicker film.
Sputtering cannot satisfy our needs, so we shifted our development concept to a thinly applicable paste.
Concept of the development
- A thinly applicable conductive paste for shielding
At first, we investigated printed-type paste with a solventless conductive paste selected for being nonvolatile.
However, the solventless system, since there is no volatile component, leads to the thick coated film.
For thin coating, we selected a solvent system with a low viscosity (existing technology for NAMICS) with a thin coating process (spray technique which was acquired). - Sprayable (low viscosity), high shielding property (high conductivity)
We aimed for low viscosity which is a trade-off with high conductivity, a core technology of NAMICS that we took advantage of. - Viscosity
For printing of conductive paste 500 to 30 Pa·s a core technology of NAMICS For dispensing of conductive paste 50 to 10 Pa·s a core technology of NAMICS
Acquisition of new technology
For spray coating of conductive paste less than 1 Pa·s
Results and Findings
- Through selecting a low viscosity resin, a filler which can lower viscosity and resistance, the shape of the filler, and a solvent, we have successfully developed a sprayable conductive paste.
- Our newly developed paste provided a film with 5 to 6 µm upper thickness and 3 to 4 µm side thickness to our target of 10 µm or less film thickness.
| Exhibition | ICEP 2018 |
|---|---|
| Presentation title | Sprayable silver paste with good shielding characteristics in high frequency band |