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Cleaning-free activated resinous composition and method for surface mounting using the same




Title: Cleaning-free activated resinous composition and method for surface mounting using the same.
Abstract: Activated resinous composition contains, on the basis of epoxy resin being solid at a room temperature of 100 parts by weight, carboxylic acid compound of 1 to 10 parts by weight, hardening agent of 1 to 30 parts by weight, a hardening reaction initiation temperature of said hardening agent being 150° C. or higher, and solvent of 10 to 300 parts by weight. ...


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USPTO Applicaton #: #20110031300
Inventors: Kazunori Kitamura, Yasuhiro Takase


The Patent Description & Claims data below is from USPTO Patent Application 20110031300, Cleaning-free activated resinous composition and method for surface mounting using the same.

BACKGROUND

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OF THE INVENTION

The present invention relates to an activated resinous composition useful for mounting of flip-chip or the like and a method for surface mounting using this activated resinous composition.

Conventionally, surface mounting technologies for various parts such as BGA parts have been carried out by a method comprising the steps of fluxing a printed wiring board; mounting BGA parts on the printed wiring board; reflow soldering; and cleaning and removing flux; filling space between the printed wiring board and the BGA parts with an underfill resin and hardening the underfill resin. The flux containing a compound having a carboxylic acid such as a rosin resin as an activator is well known (PATENT DOCUMENT 1, claim 2).

Recently, the number of chips mounted on the BGA part tends to increase for functional advancement and a body size of the BGA part correspondingly tends to grow in size.

However, having grown in size, the BAG part itself may interface with the desired cleaning effect and leave unremoved flux (flux residue) behind in the step of cleaning and removing flux. Consequently, there has been possibility that the activator ingredient contained in flux residue might cause corrosion reaction in the subsequent step of heat hardening of the underfill resin.

To overcome such problem, cleaning-free flux (flux free from requirement of cleaning) characterized in that the activator has active force sufficiently low to restrict possibility of corrosion has already been proposed (PATENT DOCUMENT 2). However, when such cleaning-free flux is used, this cleaning-free flux itself may generate cracked gas in the step of heat hardening the underfill resin and, in consequence, destroy the BGA part.

With the BGA part having grown in size, joints in the BGA part may interfere with a desired filling effect in the step of filling the underfill resin. Particularly when there are surface irregularities (e.g., circuit irregularities and/or solder mask irregularities) on the surface of the printed wiring board, it is often impossible to fill every hole and corner of the irregularities completely with the underfill resin and, as a consequence, voids and/or unfilled space may leave behind, significantly deteriorating quality and reliability of the product. Furthermore, if deficiency such as void is overlooked and the subsequent step of hardening the underfill resin, it will be no more possible to repair the product and such faulty product must be scrapped. This leads directly to reduction of yielding percentage.

[PATENT DOCUMENT 1] Japanese Patent Application Laid-Open Publication No. 2004-152936 [PATENT DOCUMENT 2] Japanese Patent Application Laid-Open Publication No. 2002-237676

SUMMARY

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OF THE INVENTION

In view of the problem as has been described above, it is an object of the present invention to provide an activated resinous composition improved so as to produce effects as will be described below.

1) In a method for surface mounting, a step of flux cleaning can be eliminated not only to reduce a manufacturing cost but also at to improve the productivity.

2) Neither gas bubble nor void space is present in a coated resinous layer after hardened and thus reliability of the product can be improved.

3) The coated resinous layer after hardened exhibits sufficiently high thermal stability to eliminate an apprehension that the coated resinous layer might cause corrosion reaction and/or generate cracked gas on heating (e.g., in the step of heat hardening the underfill resin).

4) Filling of the underfill resin can be facilitated. Consequentially, even when a BGA part having a large body size is mounted, there is no possibility that gas bubble, void or the other unfilled space might be left in regions filled with the underfill resin and hardened. In this way, reliable joint (adhesion) can be assured and reliability of the product can be improved.

The object set forth above is achieved by the present invention developed by the inventor on the basis of experimental findings.

The present invention on a first aspect thereof provides an activated resinous composition containing, on the basis of an epoxy resin being solid at a room temperature of 100 parts by weight, a carboxylic acid compound of 1 to 10 parts by weight, a hardening agent of 1 to 30 parts by weight, a hardening reaction initiation temperature of the hardening agent being 150° C. or higher, and a solvent of 10 to 300 parts by weight.

The present invention on a second aspect thereof provides a method for surface mounting comprising the steps of coating at least soldered surface of a printed wiring board with the activated resinous composition defined by the first aspect of the present invention, loading the printed wiring board with a part to be surface mounted, subjecting this to reflow soldering and heat hardening the coated resinous layer.

The present invention on a third aspect thereof provides a method for surface mounting further including a step of drying and/or heating the coated resinous layer at a temperature corresponding to a softening point or higher but lower than the hardening reaction initiation temperature before the printed wiring board is loaded with the part to be surface mounted.

The present invention on a fourth aspect thereof provides a method for surface mounting further including a step of filling and hardening the underfill resin after the coated resinous layer has been heat hardened.

The activated resinous composition according to the present invention may be used to obtain the effects as will be described below.

1) In the method for surface mounting, a step of flux cleaning can be eliminated not only to reduce a manufacturing cost but also at to improve the productivity.

2) Neither gas bubble nor void space is present in the coated resinous layer after hardened and thus reliability of the product can be improved.

3) The coated resinous layer after hardened exhibits sufficiently high thermal stability to eliminate an apprehension that the coated resinous layer might cause corrosion reaction and/or generate cracked gas on heating (e.g., in the step of heat hardening the underfill resin).

4) Filling of the underfill resin can be facilitated. Consequentially, even when the BGA part having a large body size is mounted, there is no possibility that gas bubble, void or the other unfilled space might be left in regions filled with the underfill resin and hardened. In this way, reliable joint (adhesion) can be assured and reliability of the product can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

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FIG. 1 is a plan view of a printed wiring board employed in an embodiment of the present invention (A) and a sectional view taken along the line a-a′ (B) in FIG. 1A;

FIG. 2 is a bottom plan view of a BGA part employed in the embodiment of the present invention (A) and a sectional view taken along the line a-a′ (B) in FIG. 2A and

FIG. 3 is a plurality of sectional views illustrating respective steps of a surface mounting process according to the present invention.

DETAILED DESCRIPTION

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OF THE PREFERRED EMBODIMENTS

Details of the present invention will be described on the basis of the preferred embodiments.

An activated resinous composition according to the present invention contains an epoxy resin which is solid at room temperature. The epoxy resin functions as a matrix resin. In addition, the epoxy resin also to react with an activator which will be described later in more detail in the course of hardening reaction and thereby to deactivate the activator. Thereby the coated resinous layer after hardened exhibits sufficiently high thermal stability to eliminate an apprehension that the coated resinous layer might cause corrosion reaction and/or generate cracked gas on heating (e.g., in the step of heat hardening the underfill resin). Softening point of the epoxy resin is preferably in a range of 70 to 150 (More preferably in a range of 80 to 100) ° C. More specifically, the epoxy resin may be selected from the group consisting of various cresol novorac-type epoxy resins, dicyclopentadiene-based epoxy resins, bisphenol-A-type solid epoxy resins and solid alicyclic epoxy resins.




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stats Patent Info
Application #
US 20110031300 A1
Publish Date
02/10/2011
Document #
File Date
12/31/1969
USPTO Class
Other USPTO Classes
International Class
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Drawings
0




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San-ei Kagaku Co., Ltd.


Browse recent San-ei Kagaku Co., Ltd. patents



Metal Fusion Bonding   Process   Plural Joints   Of Electrical Device (e.g., Semiconductor)   Simultaneous Bonding Of Multiple Joints (e.g., Dip Soldering Of Printed Circuit Boards)   Component Terminal To Substrate Surface (i.e., Nonpenetrating Terminal)   Lead-less (or "bumped") Device  

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20110210|20110031300|cleaning-free activated resinous composition and surface mounting using the same|Activated resinous composition contains, on the basis of epoxy resin being solid at a room temperature of 100 parts by weight, carboxylic acid compound of 1 to 10 parts by weight, hardening agent of 1 to 30 parts by weight, a hardening reaction initiation temperature of said hardening agent being |San-ei-Kagaku-Co-Ltd
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