This application claims the priority benefit of Taiwan application serial no. 100109743, filed on Mar. 22, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.
1. Technical Field
The technical field relates to a flexible circuit board, more particularly to a ultrafine circuit applicable in a flexible circuit board.
2. Related Field
Nowadays, most of the flexible circuit boards are fabricated by subtractive process, in which a photoresist (PR) is first coated onto a flexible copper clad laminate. Subsequent to the exposure and development processes, the required circuit pattern is transferred to the photoresist. The patterned photoresist is then used as a mask and wet etching is performed on the copper clad layer to form a circuit having the required pattern on the flexible substrate. However, affected by side etching, the copper circuit may have a trapezoid cross-sectional profile. The adverse effect of side etching is exacerbated with the increase in thickness of the copper foil layer or the fineness of the line width. In certain serious situations, an inverted triangle cross-sectional profile can happened to the copper circuit, and then make the subsequent configuration of devices become difficult, and poor signal transmission and reduction of the product yield. Therefore, for matching the trend of continuous thinning, lighting and down-sizing of electronic products, a further reduction of line width will require the application of a thinner copper layer. However, when the thickness of the copper layer is too thin (<8 μm), a parasitic copper rigidity—handability problem will make the manufacturing process become more difficult.
In order to improve the above mentioned handability of the thinner foil, wherein the application of the most popular subtractive process can be continued. A copper foil attached with carrier (hereafter named carrier-attached copper foil in abbreviation) has been developed through a support of carrier film with more rigidity and releasable capability after high temperature lamination processing. However, the highest operation temperature for the currently commercially available carrier-attached copper foil is only 300° C., which is still not enough for the high temperature and long duration (>360° C. for 1 hour) requirement of polyimide casting process. Moreover, even after being separated, the carrier foil is not usable again. Accordingly, by now, a carrier-attached copper foil is still expensive and unpopular. As a result, for the fabrication of LCD-COF (Chip On Flex), in which highly fine pattern is demanded, the industry generally uses the imported flexible copper clad laminate formed by sputtering process. A sputtering processed product, attributed to its necessity of passing a vacuum process, is not only expensive, but also parasitic with some undesirable properties, such as low peeling strength and low thermal stability, which would hinder the further development of fine pattern flexible circuit. Accordingly, the development of a carrier-attached copper foil remains an attention focus in the industry.
An exemplary embodiment of the disclosure provides a fabrication method of a flexible circuit board, in which ultrafine circuit is provided and low production cost is achieved.
An exemplary embodiment of the disclosure provides a fabrication method of a flexible circuit board which includes at least the following process steps. A metal carrier foil is provided. The surface of the metal carrier foil includes a metal oxide layer, and the metal oxide layer is comprised of the oxidation product of the metal carrier foil. Electroplating is performed on the metal oxide layer to form a conductive seed layer. After casting an organic insulating material or its precursor resin solution onto the conductive seed layer, followed by a baking and a hardening process, a flexible organic insulating layer is formed. The metal carrier foil is then peeled at the interface between the metal carrier foil and the conductive seed layer. The resulting seed layer and the insulating layer together form a flexible metal clad laminate. A patterned circuit is then formed on the flexible metal clad laminate.
Another exemplary embodiment of the disclosure provides a fabrication method of a flexible circuit board which includes at least the following process steps. A metal carrier foil is provided. The surface of the metal carrier foil includes a metal oxide layer, and the metal oxide layer is comprised of the oxidation product of the metal carrier foil. Electroplating is performed on the metal oxide layer to form a copper layer used for forming a circuit pattern. A thermal barrier layer is electroplated onto the copper layer. After casting an organic insulating material or its precursor resin solution (such as polyimide) onto the thermal barrier layer, followed by a baking and a hardening process, a flexible organic insulating layer is formed. The metal carrier foil is peeled off at the interface between the metal carrier foil and the copper layer to complete the fabrication of a flexible copper clad laminate. After further patterning the copper layer and the thermal barrier layer, a flexible circuit board can be made.
According to an exemplary embodiment of the fabrication method of a flexible circuit board of the disclosure, the metal oxide on the surface of the metal carrier foil allows the metal carrier foil to be easily peeled off subsequent to the high temperature casting process for forming the flexible insulating substrate. Accordingly, the fabrication method of a flexible circuit of the exemplary embodiments of the disclosure is applicable to the high temperature production (400° C. for 2 hours) of flexible metal clad laminate with the ultrathin (<8 μm) metal layer for producing an ultrafine flexible circuit.
The disclosure and certain merits provided by the disclosure can be better understood by way of the following exemplary embodiments and the accompanying drawings, which are not to be construed as limiting the scope of the disclosure.
Continuing to
Referring to
Referring to
According to the fabrication method of a flexible circuit board in the exemplary embodiments of the disclosure, with the application of the metal carrier foil 110 comprising a metal oxide layer 112, a releasable layer is not required. The metal carrier foil 110 can be recycled to lower the production cost. Moreover, the patterned circuit 152 is formed after the high temperature cyclization formation of the insulating layer 130, the achievability and the yield of fine circuit pattern are enhanced.
Thereafter, referring to
Referring to
Referring to
Referring to
Continuing to
Referring to
According to the above, the exemplary embodiments of the disclosure, a releasable layer is not required for the metal carrier foil 110 comprising the metal oxide layer 112 in the fabrication of a flexible circuit board. Further, the metal carrier foil 110 is recyclable to lower the production cost.
Referring to
Referring to
In the following experiments, a flexible circuit board is fabricated according the fabrication method as shown in
According to the fabrication method of a flexible circuit board of the exemplary embodiments, a releasable layer is not required for the metal carrier foil. Hence, by providing an appropriate support for the ultra-thin metal layer, an ultrafine pattern circuit can be completed. Moreover, after cyclization process, the peeled metal carrier foil still can be recycled to lower the cost. Furthermore, the step in forming the circuit with the appropriate metal layer is performed subsequent to the high temperature cyclization process for forming the insulating layer. Accordingly, grain coarsening of the metal layer is reduced, while the yield of the circuit is greatly enhanced. The application of the fabrication method in the exemplary embodiments of the disclosure in the fabrication of flexible circuit provides beneficial and favorable results.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
---|---|---|---|
100109743 A | Mar 2011 | TW | national |
Number | Name | Date | Kind |
---|---|---|---|
3341916 | Greene | Sep 1967 | A |
3998601 | Yates et al. | Dec 1976 | A |
4353954 | Yamaoka et al. | Oct 1982 | A |
5066366 | Lin | Nov 1991 | A |
5262247 | Kajiwara et al. | Nov 1993 | A |
5840170 | Nagy | Nov 1998 | A |
6346335 | Chen et al. | Feb 2002 | B1 |
6447929 | Wang et al. | Sep 2002 | B1 |
6465742 | Hiraoka et al. | Oct 2002 | B1 |
6569543 | Brenneman et al. | May 2003 | B2 |
6596391 | Smith | Jul 2003 | B2 |
6689268 | Chen et al. | Feb 2004 | B2 |
6770976 | Wang et al. | Aug 2004 | B2 |
20030111734 | Kobayashi et al. | Jun 2003 | A1 |
20050142374 | Chen et al. | Jun 2005 | A1 |
20090136725 | Shimokawa et al. | May 2009 | A1 |
20100330504 | Irisawa et al. | Dec 2010 | A1 |
20120155054 | McColloch | Jun 2012 | A1 |
Number | Date | Country |
---|---|---|
1294004 | Jan 2007 | CN |
101122035 | Feb 2008 | CN |
101322447 | Dec 2008 | CN |
101933408 | Dec 2010 | CN |
2000-309898 | Nov 2000 | JP |
2002-292788 | Oct 2002 | JP |
2003-181970 | Jul 2003 | JP |
2004124214 | Apr 2004 | JP |
2005-307270 | Nov 2005 | JP |
2007-186781 | Jul 2007 | JP |
2007-314855 | Dec 2007 | JP |
2009-004423 | Jan 2009 | JP |
2009-090570 | Apr 2009 | JP |
I263461 | Oct 2006 | TW |
I276708 | Mar 2007 | TW |
200806810 | Feb 2008 | TW |
200939920 | Sep 2009 | TW |
Entry |
---|
Yamamoto et al., “Allowable copper thickness for fine pitch patterns formed by a subtractive method”, Circuit World, Oct. 26, 2000, pp. 6-12, vol. 27, Issue 1. |
Sakairi et al., “Effect of Potential, Temperature, and Fluoride Ions on the Repassivation Kinetics of Titanium in Phosphate Buffered Saline Solution with the Photon RuptureMethod”, Laser Chemistry, May 5, 2009, pp. 1-8. |
Abdel-Gaber et al., “Kinetics and thermodynamics of aluminium dissolution in 1.0M sulphuric acid containing chloride ions”, Materials Chemistry and Physics, Sep. 7, 2005, pp. 291-297. |
Go Okamoto, “Passive Film of 18-8 Stainless Steel Structure and Its Function”, Corrosion Science, 1973, pp. 471-489, vol. 13. |
Abreu et al., “The effect on Ni in the electrochemical properties of oxide layers grown on stainless steels”, Electrochimica Acta, 2006, pp. 2991-3000. |
Cheskis et al., “Ultra Thin Copper Foil for HDI Applications”, Circuit Tree, Nov. 1, 2004, pp. 1-17. |
“Notice of Allowance of Taiwan Counterpart Application”, issued on Aug. 16, 2013, p. 1-p. 3. |
“Office Action of China Counterpart Application”, issued on Jun. 4, 2014, p. 1-p. 5. |
Number | Date | Country | |
---|---|---|---|
20120241082 A1 | Sep 2012 | US |