News Column

Researchers Submit Patent Application, "Method of Manufacturing Connection Structure", for Approval

September 3, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Kojima, Ryoji (Tochigi, JP), filed on April 2, 2012, was made available online on August 21, 2014.

The patent's assignee is Dexerials Corporation.

News editors obtained the following quote from the background information supplied by the inventors: "Double-sided flip-chip mounted connection structures are known in which IC chips (Integrated Circuit Chips) are flip-chip mounted onto the respective front and rear surfaces of a wiring substrate with an anisotropic conductive adhesive film (ACF) or a non-conductive adhesive film (NCF) interposed therebetween. Such a double-sided mounted type connection structure is made in a manner such that the ACF or NCF is temporarily affixed onto one surface of the wiring substrate; an IC chip is aligned and temporarily mounted thereon and then subjected to thermal pressure bonding for flip-chip mounting with a heating and pressing tool; and then, another IC chip is flip-chip mounted onto the other surface in the same manner.

"However, there arose a problem that the first flip-chip mounting on the one surface caused warpage not only on the wiring substrate but also on the IC chip itself; the another IC chip was aligned with reduced accuracy when the another IC chip was flip-chip mounted onto the other surface; and the IC chips were difficult to be accurately subjected to thermal pressure bonding with the heating and pressing tool. This problem has become noticeable as the IC chip and the wiring substrate have been increasingly reduced in thickness in recent years.

"It has been thus practiced to flip-chip mount the IC chips not on one surface and then the other surface in sequence but on both the surfaces at a time. That is, it has been suggested that the thermosetting anisotropic conductive adhesive film (ACF) or non-conductive adhesive film (NCF) is temporarily affixed onto each of the front and rear surfaces of the wiring substrate, and then the IC chips are each temporarily mounted thereon to prepare a half-finished connection structure; the half-finished connection structure is subsequently placed on a placement receiving base which has a placement surface made of a rubber material or the like and which has heating means; and then while the half-finished product is being heated from the side of the placement receiving base, the IC chips on the front surface are pressed with a pressure applying tool having an elastic pressing surface (Patent Literature 1)."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "Technical Problem

"However, there was a problem with Patent Literature 1 that heating the ACF or NCF placed on the side of the placement receiving base so as to be optimally hardened in order to provide good connection for the ACF or NCF placed on the side of the placement receiving base would cause the ACF or NCF placed on the side of the pressure applying tool to be insufficiently heated and thus not sufficiently hardened, thereby leading to lack of connection reliability. On the other hand, heating the ACF or NCF placed on the side of the pressure applying tool so as to be optimally hardened in order to provide good connection for the ACF or NCF placed on the side of the pressure applying tool would cause, this time, the ACF or NCF placed on the placement receiving base to be excessively heated. This would lead to a quick increase in the melting viscosity causing an adhesive component to be hardened without being sufficiently removed from between the IC chip and the wiring substrate. Thus, this raised a problem or lack of connection reliability.

"It is an object of the present invention to solve the conventional technical problems mentioned above. Further, it is an object of the present invention to enable a connection structure, which includes a wiring substrate, a first electronic component flip-chip mounted on the front surface thereof with an ACF or NCF disposed therebetween, and a second electronic component flip-chip mounted on the rear surface, to be fabricated by allowing the ACF or NCF on both the surfaces to be hardened under respectively optimum hardening conditions.

"Solution to Problem

"The inventor has paid attention to the fact that when electronic components were temporarily mounted onto both the surfaces of a wiring substrate with adhesive films disposed respectively therebetween and then the electronic components placed on both the surfaces were flip-chip mounted thereto by heating the same from one of the surfaces, the adhesive film disposed on the front surface of the wiring substrate to be heated is heated to a higher temperature than that of the adhesive film disposed on the rear surface of the wiring substrate. Then, the inventor has found that the aforementioned object could be achieved by employing two types of adhesive films having different curing temperatures so as to dispose the adhesive film having a higher curing temperature on the front surface of the wiring substrate to be heated. This finding leads the inventor to the completion of the present invention.

"That is, the present invention provides a method of manufacturing a connection structure, the connection structure including a wiring substrate, a first electronic component flip-chip mounted on a front surface thereof, and a second electronic component flip-chip mounted on a rear surface, the method including the following steps (a) to (d):

"Step (a)

"a step of temporarily mounting the first electronic component on the front surface of the wiring substrate with a first adhesive film disposed therebetween;

"Step (b)

"a step of temporarily mounting the second electronic component on the rear surface of the wiring substrate with a second adhesive film disposed therebetween, the second adhesive film having a curing temperature lower than the curing temperature of the first adhesive film;

"Step

"a step of placing, on a pressure bonding receiving base, the wiring substrate on which the first electronic component and the second electronic component are temporarily mounted; and

"Step (d)

"a step of heating the first electronic component while pressing the same against the wiring substrate with a heating and pressing tool from the side of the first electronic component, thereby mounting at a time the first electronic component and the second electronic component onto the respective front and rear surfaces of the wiring substrate. In addition, the present invention provides a connection structure manufactured by the manufacturing method.

"Advantageous Effects of Invention

"In the manufacturing method according to the present invention, the adhesive film disposed on the front surface of the wiring substrate to be heated is heated to a temperature higher than that of the adhesive film disposed on the rear surface of the wiring substrate. Thus, two types of adhesive films having different curing temperatures are employed so as to dispose the adhesive film having the higher curing temperature on the front surface of the wiring substrate on the side thereof to be heated. This enables the adhesive films on both the surfaces of the wiring substrate to be heated at a time to the respectively optimum curing temperatures. It is thus possible to provide the double-sided flip-chip mounted wiring substrate for electronic components with improved connection reliability without causing any warpage on the wiring substrate and the IC chips.

BRIEF DESCRIPTION OF DRAWINGS

"FIG. 1 is an explanatory view of a manufacturing method according to the present invention.

"FIG. 2 is an explanatory view of a manufacturing method according to the present invention.

"FIG. 3 is a cross-sectional view of a laminated-type electronic component.

"FIG. 4 is an explanatory view of a manufacturing method according to the present invention.

"FIG. 5 is an explanatory view of a manufacturing method according to the present invention.

"FIG. 6 is an explanatory view of a manufacturing method according to the present invention.

"FIG. 7 is a cross-sectional view of a connection structure according to the present invention.

"FIG. 8 is a DSC chart showing the curing temperature of an adhesive film."

For additional information on this patent application, see: Kojima, Ryoji. Method of Manufacturing Connection Structure. Filed April 2, 2012 and posted August 21, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=3817&p=77&f=G&l=50&d=PG01&S1=20140814.PD.&OS=PD/20140814&RS=PD/20140814

Keywords for this news article include: Dexerials Corporation, Electronic Components.

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Source: Electronics Newsweekly


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