News Column

"Lead Frame" in Patent Application Approval Process

August 6, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent application by the inventor ISHIBASHI, Takahiro (Fukuoka, JP), filed on January 2, 2014, was made available online on July 24, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application is assigned to Mitsui High-tec , Inc.

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates to a lead frame used for a semiconductor apparatus, especially for a QFN (Quad Flat Non-Leaded) semiconductor apparatus which is manufactured using a MAP (Molded Array Process) mold-forming technique in which a plurality of semiconductor apparatuses are collectively sealed with resin.

"A QFN semiconductor apparatus is manufactured by using the MAP mold-forming technique which seals a plurality of semiconductor apparatuses with resin collectively. First, a lead frame in which a plurality of lead parts of adjacent unit lead frames are interconnected via a connecting bar is prepared as a MAP lead frame. A semiconductor device is bonded on a mounting part of the lead frame, and the semiconductor device and leads of the lead frame are connected via wires. Then, the lead frame, the semiconductor device and the wires are sealed with resin. Subsequently, the connecting bar (also referred to as a dam bar) is removed by dicing, thereby splitting into individual unit lead frames.

"If the thickness of the connecting bar is large, a load to a rotary blade is increased when performing the dicing, thereby accelerating galling of the rotary blade. Thus, a dicing capability is deteriorated and cutting burr may be produced.

"JP-A-2005-166695 describes a technique for performing half-etching from a rear side on the whole of the dam bar except for a rear side of a device mounting part and a rear-side terminal part of the lead. In this way, it is possible to suppress the acceleration of galling of the rotary blade when performing the dicing, and prevent the cutting burr from being produced."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventor's summary information for this patent application: "In recent years, a semiconductor apparatus grows in size due to the increase of pins and a lead frame is thinned in conformity with thinning the semiconductor apparatus. On the other hand, a lead frame tends to be larger in area in order to increase the number of unit lead frames obtained from each piece of lead frames. Accordingly, in a structure in which the whole of the connecting bar is thinned as described in JP-A-2005-166695, a problem is raised that the connecting bar, which serves as a connection of the unit lead frames, and its neighboring parts cannot be tolerant to an external force, thereby being deformed. The connecting bar is arranged to surround the unit lead frame and includes a crossing point at which a longitudinal connecting bar and a transverse connecting bar are crossed. The unit lead frame includes a plurality of leads which is divided into four lead-groups. The connecting bar is deformed, especially between the crossing point and the lead-groups.

"JP-A-2005-166695 describes a technique by which a dam bar of a lead frame is thinned by half-etching and a part thicker than a thinned portion is formed on the dam bar along the direction of dicing. In this technique, it is possible to prevent the cutting burr from being produce when performing dicing while securing the strength of the dam bar. In this method, however, although the strength of the dam bar is secured, since the thicker part is formed consecutively to the dam bar, a problem is raised that the cutting burr may be produced because the load to the rotary blade cannot be sufficiently lowered when performing dicing. In addition, an etching process becomes difficult because an etching solution is hardly infiltrated into a portion to be etched which is provided between the lead and the portion thicker than the thinned portion.

"The present invention has been made in consideration with the above circumstance, and an object of the present invention is to provide a lead frame having a connecting bar, the shape of which can be formed with simple etching process, so as to suppress the production of cutting burr in dicing and to prevent a periphery of a crossing point of connecting bars from being deformed.

"A first aspect of the present invention provides a lead frame, including: a plurality of unit lead frames arranged in a matrix; a plurality of leads aligned along sides of each of the plurality of unit lead frames, a rear surface of the leads being exposed; a connecting bar via which the leads of adjacent ones of the plurality of unit lead frames are connected, the connecting bar including a longitudinal connecting bar, a transverse connecting bar and a crossing part at which the longitudinal connecting bar and the transverse connecting bar are crossed; a dicing part including the connecting bar and a part of the leads, to be cut along a dicing line; a half-etching part formed along the dicing part, and being smaller in width than the dicing part; and a strength retention part formed in the half-etching part and extended from the crossing part of the connecting bar at least to an end lead located closest to the crossing part among the leads of the unit lead frame adjacent to the crossing part.

"According to a second aspect of the present invention, the lead frame may be configured so that the strength retention part includes a first strength retention part formed along a dicing direction of the connecting bar and a second strength retention part formed along the leads, and the second strength retention part is formed between a pair of leads connected to each other via the connecting bar.

"According to a third aspect of the present invention, the lead frame may be configured so that the first strength retention part is formed consecutively to the second strength retention part.

"According to a fourth aspect of the present invention, the lead frame may be configured so that the first strength retention part has a quarter to half width of the connecting bar.

"According to a fifth aspect of the present invention, the lead frame may be configured so that the second strength retention part has a quarter to half width of the connecting bar

"According to a sixth aspect of the present invention, the lead frame may be configured so that a distance between an end of the half-etching part at a side of the first strength retention part and an end of the half-etching part at a side of the lead is 0.5 to 0.75 times larger than a width of the connecting bar.

"According to the lead frame as mentioned above, the thickness of metal of the dicing part to be cut with the rotary blade is thinned. Since a load to the rotary blade applied when performing dicing is reduced, production of cutting burr is suppressed and a life of the rotary blade is prolonged. Further, since the strength retention part is formed in the half-etching part and extended from the crossing part of the connecting bar to the end lead located closest to the crossing part among the leads of the unit lead frame adjacent to the crossing part, it is possible to enhance the strength on a part on which a stress is most likely concentrated. Thus, it is unnecessary more than necessary to increase the thickness of the metal in the dicing part, and the lead frame is prevented from being deformed. In addition, since the strength of the lead frame is increased, it is harmonized with growing in size of the semiconductor apparatus and the thinning of the lead frame. In addition, since the strength retention part includes the first strength retention part and the second strength retention part, the connecting bar is tolerant to a stress applied from multi-directions, and moreover, etching process becomes simple for a part between the first strength retention part and a widthwise end of the half-etching part of the lead.

BRIEF DESCRIPTION OF THE DRAWINGS

"In the accompanying drawings:

"FIG. 1 is a plan view of a lead frame according to a first embodiment of the present invention;

"FIG. 2A is a plan view showing a rear side in a periphery of a crossing part of a connecting bar of the lead frame according to the first embodiment of the present invention;

"FIG. 2B is a cross-sectional view taken along a line IIB-IIB in FIG. 2A;

"FIG. 3 shows a dicing process of the lead frame according to the first embodiment of the present invention;

"FIG. 4A is a plan view showing a rear side in a periphery of a crossing point of connecting bars of a lead frame according to a second embodiment of the present invention;

"FIG. 4B is a cross-sectional view taken along a line IVB-IVB in FIG. 4A; and

"FIG. 4C is a cross-sectional view taken along a line IVC-IVC in FIG. 4A."

URL and more information on this patent application, see: ISHIBASHI, Takahiro. Lead Frame. Filed January 2, 2014 and posted July 24, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4939&p=99&f=G&l=50&d=PG01&S1=20140717.PD.&OS=PD/20140717&RS=PD/20140717

Keywords for this news article include: Electronics, Semiconductor, Mitsui High-tec Inc..

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Source: Electronics Newsweekly


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