Patent Application
20110159317
This Application claims priority of Taiwan Patent Application No. 98144939, filed on Dec. 25, 2009, the entirety of which is incorporated by reference herein.
The disclosure generally relates to a technique for suppressing electromagnetic interference and more particularly to a flexible sheet with high magnetic permeability and fabrication method thereof.
With the miniaturization of electrical circuits in communications, consumer electronics and computer technology, the suppressing of electromagnetic interference (EMI) has become increasingly important. EMI is type of noise interference which obstructs signals. The interference includes radiating noise from a source through space and conducting noise through conductive cables to interfere. Conducting noise is usually avoided using capacitors, inductors, EMI filters or EMI suppression sheets formed with a ring shape to act as an EMI core. Radiating noise is usually reduced by absorption using an EMI suppression sheet or reflection using a conductive sheet. In fact, EMI suppression sheets can be used to eliminate both radiating and conducting noises. Transmission integrated circuits in high speed signals, wiring and cables need to reduce radiating and conducting EMI noise by means of EMI suppression sheets.
A conventional flexible EMI suppression sheet with magnetic permeability is formed by the steps which comprise mixing and blending a magnetic powder material and a resin or a rubber to form a slurry or a gel and shaping using a doctor blade or pressing using a roller, to form a flexible sheet. The conventional EMI suppression sheet, however, has low magnetic permeability, due to the fact that it requires a certain percentage of resin or rubber. Therefore, the shielding effect of a conventional EMI suppression sheet is not good. In order to overcome the issue of low magnetic permeability, one method used is to change the magnetic powder material and another method used is to increase the filling ratio of the magnetic powder material. However, due to limitations, it is difficult to further increase the filling ratio of the magnetic powder material.
One embodiment relates to a flexible sheet with high magnetic permeability, including a magnetic ferrite sintering sheet including a plurality of pieces separated by micro gaps and a first flexible layer attached to a first side of the magnetic ferrite sintering sheet, wherein the pieces of the magnetic ferrite sintering sheet comprise a first protruding and recessing structure and a second protruding and recessing structure at opposite sides of one of the micro gaps, and the first protruding and recessing structure and the second protruding and recessing structure are matched with each other.
Another embodiment relates to a method for fabricating a flexible sheet with high magnetic permeability, including the steps of forming a magnetic ferrite sintering sheet, attaching a first flexible layer on a first side of the magnetic ferrite sintering sheet, and performing a hot pressing process, wherein the magnetic ferrite sintering sheet is crushed to a plurality of pieces during the hot pressing process.
The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein,
In order to address the issue of low magnetic permeability, one of embodiments implements a sintering sheet of magnetic ferrite material as a principle part. A top layer, which is a glue layer comprising magnetic ferrite fine powders, is bonded onto the sintering sheet of magnetic ferrite material. A bottom layer, which is a glue layer comprising magnetic ferrite fine powders, is bonded onto the underside of the sintering sheet of magnetic ferrite material. The middle layer, the top layer and the bottom layer are then pressed to mold a sandwich structure. Following, a hot press hardening process is performed to form a flexible sheet with high magnetic permeability. The resulting flexible sheet has increased magnetic permeability and shield effect when compared to a conventional EMI suppression sheet.
A method for forming an EMI suppression sheet with high magnetic permeability is illustrated in accordance with
Thereafter, a step for forming a magnetic ferrite sintering sheet 100 is performed. In one embodiment, the Ni—Cu—Zn ferrite powder with high magnetic permeability is mixed with a binder, such as a polyvinyl butyral (PVB) resin or acrylic resin, to form a thick slurry, in which the mixing ratio can be 80-90 wt % of ferrite powder and 20-10 wt % of binder. Next, a doctor blade casting method is performed to form a green sheet. The green sheet is then debinded and sintered at a high temperature to form an Ni—Cu—Zn ferrite sintering sheet 100 which may have a thickness of about 30-150 μm, more preferably 30-100 μm.
A first flexible layer 104 and a second flexible layer 106 are attached onto a top surface and a bottom surface of the magnetic ferrite sintering sheet 100, respectively, to form a sandwich structure. Note that the invention includes, but is not limited to forming flexible layers both on the top surface and the bottom surface of the magnetic ferrite sintering sheet. In another embodiment of the invention, only the top surface or the bottom surface of the magnetic ferrite sintering sheet is attached with a flexible layer. In addition, the invention is not limited to a specific flexible layer. The flexible layer can be an adhesive film or a magnetic metal sheet, wherein the adhesive film can be any adhesive flexible material, such as polyvinyl chloride (PVC), polyurethane (PU), acrylic, hot-melt adhesive, epoxy resin, liquid silicone resin or combinations thereof. In one embodiment of the invention, the adhesive material of the top flexible layer and/or the bottom layer on the top side and/or the bottom side of the magnetic ferrite sintering sheet can be filled with magnetic powders, which can be a Fe—Ni—Co based metal powder, Mn—Zn, Ni—Zn, Cu—Zn, Ni—Cu—Zn, Mg—Zn, or Li—Zn ferrite materials or combinations thereof. In another embodiment, the adhesive film on the top side and/or the bottom side of the magnetic ferrite sintering sheet can be filled with a material with a high thermal conductivity coefficient, such as powders comprising Cu, Ag, Cu—Ag alloy, aluminum oxide or boron nitride. The fabricated EMI suppression sheet not only has high magnetic permeability, but also has a good heat dissipating effect. Therefore, the EMI suppression sheet can dissipate heat and suppress EMI.
Next, referring to
The EMI suppression sheet with high magnetic permeability can be applied in a device embedded substrate, a flexible inductor, a transformer, an EMI suppression device, a radio-frequency identification (RFID) tag and an EMI suppression sheet of electromagnetic parts or a magnetic shielding sheet. However, the invention is not limited thereto.
In one embodiment, because the pieces 102 of the magnetic ferrite sintering sheet 100 are formed from crushing during the hot pressing process, the pieces 102 have irregular shapes. In another embodiment of the invention, a pre-grooving step can be performed on the magnetic ferrite sintering sheet 100 before conducting the hot pressing process, wherein a plurality of grooves are formed on a surface of the ferrite sintering sheet 100. The ferrite sintering sheet 100 can be crushed along the grooves to form pieces with specific shapes during the hot pressing process. In an embodiment, length and width of the magnetic ferrite sintering sheet are within a range of between 0.5-5 mm, preferably 2-3 mm
The flexible sheet with high magnetic permeability is illustrated in accordance with
66 wt % of iron oxide, 4.7 wt % of nickel oxide, 22.7 wt % of zinc oxide, and 6.6 wt % of copper oxide were wet mixed, calcinated at 850° C., ball grinded, and dried to form a Ni—Cu—Zn ferrite powder. 88 wt % of the Ni—Cu—Zn ferrite powder and 12 wt % of PVB resin were mixed to form a thick liquid, and a doctor blade casting method was performed to fabricate a green sheet. Include mixing amounts of ferrite powder and PVB resin. The green sheet was then debinded and sintered at a high temperature of 1100° C. to form a Ni—Cu—Zn ferrite sintering sheet which had a thickness of 33 μm.
The ball grinded and dried Ni—Cu—Zn ferrite powder was then granulated, and sintered at 1100° C. and fine crushed to form a Ni—Cu—Zn ferrite fine powder. The Ni—Cu—Zn ferrite fine powder was then surface modified with a titanate coupling agent LICA38 to form a well-dispersed powder. 10 wt % of Ni—Cu—Zn ferrite powder and 90 wt % of a modified epoxy resin adhesive were mixed and blended to form an adhesive comprising the Ni—Cu—Zn ferrite fine powder.
Next, the adhesive was coated on a polyethylene terephthalate (PET) adhesive film having a releasing characteristic and the coating of the adhesive was controlled to form a layer thickness of about 10-20 μm. Thereafter, the top surface and the bottom surface of the Ni—Cu—Zn ferrite sintering sheet were attached with the PET adhesive film coated with the adhesive comprising the Ni—Cu—Zn ferrite powder, respectively, to form a sandwich structure. A hot pressing process was performed wherein the Ni—Cu—Zn ferrite sintering sheet was crushed into a plurality of pieces separated by micro gaps. Next, a hot-press hardening process was performed to complete an EMI suppression sheet with high magnetic permeability.
The EMI suppression sheet was measured using a RF Impedance/material analyzer apparatus showing high magnetic permeability 203 (at 1 MHz).
65 wt % of iron oxide, 4.4 wt % of nickel oxide, 22.3 wt % of zinc oxide, and 8.3 wt % of copper oxide were wet mixed, calcinated at 850° C., ball grinded, and dried to form a Ni—Cu—Zn ferrite powder. 88 wt % of the Ni—Cu—Zn ferrite powder and 12 wt % of PVB resin were mixed to form a thick liquid, and a doctor blade casting method was performed to fabricate a green sheet. The green sheet was then debinded and sintered at a high temperature of 1100° C. to form a Ni—Cu—Zn ferrite sintering sheet having a thickness of 50 μm.
The ball grinded and dried Ni—Cu—Zn ferrite powder was then granulated, sintered at 1100° C. and fine crushed to form a Ni—Cu—Zn ferrite fine powder. The Ni—Cu—Zn ferrite fine powder was then surface modified with a titanate coupling agent LICA38 to form a well-dispersed powder. 10 wt % of Ni—Cu—Zn ferrite powder and 90 wt % of a modified epoxy resin adhesive were mixed and blended to form an adhesive comprising Ni—Cu—Zn ferrite fine powder.
Next, the adhesive was coated on a PET adhesive film having a releasing characteristic and the coating of the adhesive was controlled to form a layer thickness of about 10-20 μm. Thereafter, the top surface and the bottom surface of the Ni—Cu—Zn ferrite sintering sheet were attached with the PET adhesive film coated with the adhesive comprising the Ni—Cu—Zn ferrite powder, respectively, to form a sandwich structure. A hot pressing process was performed wherein the Ni—Cu—Zn ferrite sintering sheet was crushed into a plurality of pieces separated by micro gaps. Next, a hot-press hardening process was performed to complete an EMI suppression sheet with high magnetic permeability.
The EMI suppression sheet was measured using a RF Impedance/material analyzer apparatus showing high magnetic permeability 228 (at 1 MHz).
65 wt % of iron oxide, 8.4 wt % of nickel oxide, 19.9 wt % of zinc oxide, and 6.7 wt % of copper oxide were wet mixed, calcinated at 750° C., ball grinded, and dried to form a Ni—Cu—Zn ferrite powder. 88 wt % of the Ni—Cu—Zn ferrite powder and 12 wt % of PVB resin were mixed to form a thick liquid, and a doctor blade casting method was performed to fabricate a green sheet. The green sheet was then debinded and sintered at a high temperature of 1050° C. to form a Ni—Cu—Zn ferrite sintering sheet which had a thickness of 52 μm.
The ball grinded and dried Ni—Cu—Zn ferrite powder was then granulated, sintered at 950° C. and fine crushed to form a Ni—Cu—Zn ferrite fine powder. The Ni—Cu—Zn ferrite fine powder was then surface modified with a titanate coupling agent LICA38 to form a well-dispersed powder. 10 wt % of Ni—Cu—Zn ferrite powder and 90 wt % of a modified epoxy resin adhesive were mixed and blended to form an adhesive comprising Ni—Cu—Zn ferrite fine powder.
Next, the adhesive was coated on a PET adhesive film having a releasing characteristic and the coating of the adhesive was controlled to form a layer thickness of 10-20 μm. Thereafter, the top surface and the bottom surface of the Ni—Cu—Zn ferrite sintering sheet were attached with the PET adhesive film coated with the adhesive comprising the Ni—Cu—Zn ferrite powder, respectively, to form a sandwich structure. A hot pressing process was performed wherein the Ni—Cu—Zn ferrite sintering sheet was crushed into a plurality of pieces separated by micro gaps. Next, a hot-press hardening process was performed to complete an EMI suppression sheet with high magnetic permeability.
The EMI suppression sheet was measured using a RF Impedance/material analyzer apparatus showing high magnetic permeability 140 (at 1 MHz).
While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
| Number | Date | Country | Kind |
|---|---|---|---|
| 98144939 | Dec 2009 | TW | national |
