Source: http://patents.com/us-7989267.html
Timestamp: 2019-01-16 00:10:15
Document Index: 761467362

Matched Legal Cases: ['application No. 2004', 'art) 3', 'art 12', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1', 'art 1']

US Patent # 7,989,267. Manufacturing method of semiconductor device and manufacturing method of lead frame - Patents.com
United States Patent 7,989,267
Ito , et al. August 2, 2011
Improvement in the reliability of a semiconductor device is aimed at. By heating a lead frame, after preparing a lead frame with a tape, until a resin molding is performed, at the temperature 160 to 300.degree. C. (preferably 180 to 300.degree. C.) for a total of more than 2 minutes in the atmosphere which has oxygen, crosslinkage density becoming high in resin of adhesives, a low molecular compound volatilizes and jumps out outside, therefore as a result, since a low molecular compound does not remain in resin of adhesives, the generation of copper migration can be prevented.
Inventors: Ito; Fujio (Hanno, JP), Suzuki; Hiromichi (Tokyo, JP), Kameoka; Akihiko (Ogose, JP), Kusukawa; Junpei (Hitachinaka, JP), Takezawa; Yoshitaka (Hitachinaka, JP)
Appl. No.: 12/104,154
11181929 Jul., 2005 7374973
Jul 16, 2004 [JP] 2004-209376
Current U.S. Class: 438/123 ; 257/E21.513
Field of Search: 438/123 257/E23.513
5851853 December 1998 Lee et al.
6858473 February 2005 Hosokawa et al.
7125750 October 2006 Kwan et al.
7132755 November 2006 Hosokawa et al.
7235888 June 2007 Hosokawa et al.
7262514 August 2007 Yoshikawa et al.
7294217 November 2007 Beatson et al.
9-153587 Jun., 1997 JP
10-163410 Jun., 1998 JP
This application is a continuation of U.S. application Ser. No. 11/181,929, filed Jul. 15, 2005 now U.S. Pat. No. 7,374,973. The present application claims priority from Japanese patent application No. 2004-209376 filed on Jul. 16, 2004, the contents of which are hereby incorporated by reference into this application.
1. A manufacturing method of a semiconductor device assembled using a lead frame which has a plurality of leads, comprising the steps of: (a) providing the lead frame comprised of copper or copper alloy, the lead frame having a chip mounting portion, the plurality of leads arranged around the chip mounting portion, and a tape steadying each of the plurality of leads, the tape being arranged over the plurality of leads via adhesives, wherein the adhesives are mixed adhesives comprised primarily of phenol resin and bismaleimide resin, and including acetaldehyde, methanol or acetone; (b) mounting a semiconductor chip on the chip mounting portion, the semiconductor chip having a main surface, and a plurality of pads formed on the main surface; (c) electrically connecting the plurality of pads of the semiconductor chip with the plurality of leads via a plurality of wires, respectively; (d) forming a sealed body for sealing the semiconductor chip, the plurality of wires, and the plurality of leads with a resin such that a part of each of the plurality of leads is exposed from the sealed body; wherein before step (b), the lead frame is heated, at a temperature between 180 degrees and 300 degrees for between 2 minutes and 5 minutes, in an atmosphere including oxygen.
2. A manufacturing method of a semiconductor device according to claim 1, wherein a thickness of the tape is 50 .mu.m.
In the conventional semiconductor device using a tape and its manufacturing method, the surface of the leads made of Cu is covered by the metal plating of about 30 micrometers thick of gold, platinum, palladium, indium, chromium, titanium, antimony, rhodium, tantalum and vanadium, the alloy containing such metal, Ag which metal ion cannot move into adhesives, etc. The insulating tape with which adhesives were applied is stuck on a lead via the protective film by metal plating. The metal plating is performed only to the surface of the lead of the taping position on which insulating tape is stuck (for example, refer to Patent Reference 2). [Patent Reference 1] Japanese Unexamined Patent Publication No. Hei 9 (1997)-153587(FIG. 1) [Patent Reference 2] Japanese Unexamined Patent Publication No. Hei 10 (1998)-163410(FIG. 1)
According to one aspect of the present invention, a manufacturing method of a semiconductor device comprises the steps of: preparing the lead frame over which a tape was stuck via adhesives containing a low molecular compound; connecting a part of the lead frame and a semiconductor chip; connecting electrically the leads of the lead frame and the semiconductor chip; and performing resin molding of the semiconductor chip; wherein after sticking the tape over the lead frame and before performing the resin molding, the lead frame is heated at a temperature of 180 to 300.degree. C. for a total of more than 2 minutes in an atmosphere which has oxygen.
According to another aspect of the present invention, a lead frame over which a tape was stuck via adhesives containing a low molecular compound is prepared; and after sticking the tape over the lead frame and before performing a resin molding, the lead frame is heated at a temperature of 180 to 300.degree. C. for a total of more than 2 minutes in an atmosphere which has oxygen.
According to other aspect of the present invention, a lead frame over which a tape was stuck via adhesives containing a low molecular compound is prepared; and after sticking the tape over the lead frame and before performing a resin molding, the lead frame is heated with 160.degree. C. .ltoreq.heating temperature .ltoreq.300.degree. C. and a heating total time >2 minutes, in an atmosphere which has oxygen.
According to other aspect of the present invention, a lead frame over which a tape was stuck via adhesives containing a low molecular compound is prepared; and after sticking the tape over the lead frame and before performing a resin molding, the lead frame is heated at a temperature of 180 to 300.degree. C. for a total of more than 2 minutes in a gas atmosphere which lowers an activation energy of a reaction of a molecule.
According to other aspect of the present invention, in a manufacturing method of a semiconductor device using a member over which substrate a conductor part which includes copper or a copper alloy was stuck via thermosetting adhesives, before performing a resin molding, the member is heated at a temperature of 180 to 300.degree. C. for a total of more than 2 minutes in an atmosphere which has oxygen.
According to other aspect of the present invention, a manufacturing method of a lead frame comprises the steps of: sticking a tape via adhesives which contain a low molecular compound over a lead frame which has a plurality of leads; after sticking the tape, heating the lead frame at a temperature of 180 to 300.degree. C. for a total of more than 2 minutes in an atmosphere which has oxygen; and shipping the lead frame.
By heating a lead frame, after sticking a tape on a lead frame and before performing a resin molding, at the temperature of 180 to 300.degree. C. for a total of more than 2 minutes in the atmosphere which has oxygen, the hardening reaction accompanied by the oxidization crosslinkage in resin of adhesives can be promoted, and crosslinkage density becoming high, a low molecular compound volatilizes and jumps out outside. Thereby, since a low molecular compound does not remain in resin of adhesives, the generation of migration can be prevented. As a result, improvement in the reliability of a semiconductor device can be aimed at.
That is, the manufacturing method of the semiconductor device of this Embodiment 1, prevents the generation of copper migration by heating a lead frame 3 in the atmosphere which has oxygen at a predetermined temperature and beyond predetermined time, after sticking a tape 1 on lead frame 3 and before performing a plastic molding, when assembling a semiconductor device using lead frame 3 on which tape 1 was stuck via adhesives 1a containing low molecular compound 1c. Since it cannot be made to volatilize when heating and volatilizing low molecular compound 1c from adhesives 1a if the circumference of adhesives 1a is surrounded by resin for sealing, by the time when a resin molding is performed, lead frame 3 is heated.
The case where adhesives 1a are thermosetting adhesives, low molecular compound 1c contained in adhesives 1a is acetaldehyde, methanol, or acetone, for example, and lead frame 3 is formed of copper or a copper alloy, is taken up, mentioned and explained as an example.
Tape 1 stops disturbance of an inner lead 3a shown in FIG. 8, and prevents deformation, etc. of inner lead 3a.
First, the mechanism which prevents copper migration by heat-treating lead frame 3 on which tape 1 was stuck is explained.
Although low molecular compounds 1c, such as methanol, are what is slightly contained in raw resin of adhesives 1a without removing completely, in order to make it volatilize outside completely as out gas, it is necessary to change solubility parameters of phenol resin, etc. shown in FIG. 2 by raising the crosslinkage density of resin by performing the hardening reaction by baking, and to press out the methanol whose solubility fell from the inside of resin.
Since it becomes a hardening reaction only by heating without oxidization by the baking in nitrogen (N2) atmosphere and by the baking in vacuum atmosphere as shown in the comparative example of FIGS. 1A to 1C in that case, as to crosslinkage 1p, many normal chain structures are formed and crosslinkage density does not fully go up (FIGS. 1A to 1B), and a solubility parameter does not change to the grade which volatilizes low molecular compounds 1c, such as methanol. As a result, low molecular compound 1c remains in the resin (C of the comparative example of FIG. 1C).
On the other hand, in the baking in the atmosphere in the air etc. which has oxygen shown in Embodiment 1 of FIGS. 1A to 1C, in order that the reaction of oxidization crosslinkage 1d may occur, sufficient crosslinkage structure is easily formed in the inside of the resin (FIGS. 1A and 1C). By this, a solubility parameter can change and methanol, i.e., low molecular compound 1c, can be pressed out from the inside of the resin. As a result, low molecular compound 1c does not remain in the resin (FIG. 1C).
Thus, it becomes possible by changing the solubility parameter of the resin by the baking in the air to remove low molecular compound 1c (for example, methanol) to which the migration-proof characteristic is reduced remarkably from adhesives 1a.
As heat treatment conditions of the baking in the air, i.e., atmosphere containing oxygen, (oxygen environment), it is thought that 160 to 300.degree. C./2-minute-plus of a heating total time are enough. According to the check test, the test result that copper migration did not occur in cases where heat-treatment was performed for 5 minutes at 200.degree. C. and for 3 minutes at 240.degree. C., respectively was obtained. In the manufacturing process of the semiconductor device using Cu lead frame with a fixed tape of a comparative example shown in FIG. 6, even if it applies a heat history to lead frame 3 in the die bonding of Step S12 for 0.7 minute at 225.degree. C., and in the wire bonding of Step S13 for 0.8 minute at 240.degree. C., respectively, copper migration has occurred. Therefore, as a total time to apply a heat history to lead frame 3, it is more than 2 minutes, and let heating temperature in that case be the temperature of 160.degree. C. or more in consideration of a margin.
On the baking conditions in the high temperature of 300.degree. C. or more, the embrittlement accompanied by the thermal decomposition reaction of an adhesives resin ingredient is caused conversely, a result in which it will be in the state where the hard cladding layer is formed in the surface, and gas cannot volatilize is brought, and it is not desirable.
Therefore, in the atmosphere which has oxygen, it becomes the processing conditions of 160 to 300.degree. C./2 minute-plus of a heating total time, and preferably, it is 180 to 300.degree. C./more than 2 minutes of a heating total time, and the heat history on the assembling process of a semiconductor device becomes appropriable for bake processing.
Next, the solubility parameter (SP value) shown in FIG. 2 is a numerical value about the polarity showing the ease of swelling of a molecule. For example, in cases where adhesives 1a are mixed adhesives of phenol resin and bismaleimide resin, if the hardening reaction of phenol resin in adhesives is promoted by heat treatment, SP value of phenol resin will fall from 11.3, and the difference from 14.5 of methanol will become large. If the difference of this SP value becomes large, methanol will go away outside.
Next, the case where the mixed adhesives of phenol resin and bismaleimide resin are used is taken up as an example as adhesives 1a. And the hardening reaction (three-dimensional crosslinking reaction) of resin, and the drop of the activation energy of a reaction by containing oxygen in the atmosphere at the time of a reaction are explained.
Adhesives 1a (phenol resin+bismaleimide resin) of tape 1 are in the soft half-hardening state which contains an unreacted functional group in large quantities where it is called B stage state, in the stage stuck on lead frame 3 shown in FIG. 8. When these unreacted functional groups react, macromolecule formation of B stage adhesives of a half-hardening state progresses.
The activation energy of the reaction which draws out hydrogen from a polymer molecule (what is called oxidation reaction) falls under oxygen content atmosphere, and oxidation reaction of a polymer molecule occurs frequently also at a comparatively low temperature. Since adhesives 1a (phenol resin+bismaleimide resin of a B stage state) of the description in this Embodiment 1 contain the unreacted functional group in large quantities, it is easy to cause oxidation reaction.
Then, by heat-treating adhesives 1a of this Embodiment 1 under oxygen content atmosphere, a reactant functional group can be made into a peroxy radical by oxidization, and the crosslinking reaction (oxidization crosslinkage 1d) which made this the starting point of the reaction is considered to progress easily. As a result, formation of three-dimensional structure and conjugated structure of an adhesives resin ingredient as shown in FIG. 4 progresses. As the proof, the hue of resin assumes the brown resulting from increase of electron transition absorption from the light yellow of B stage. When formation of three-dimensional structure progresses, sufficient crosslinkage structure is easily formed in the inside of resin, the solubility parameter can change, and low molecular compounds 1c, such as methanol, can be pressed out from the inside of resin.
As compared with this, only the heat hardening reaction of adhesives 1a (phenol resin+bismaleimide resin of a B stage state) occurs under the atmosphere which does not contain oxygen, such as nitrogen atmosphere and vacuum atmosphere. And the formation of the three-dimensional structure and conjugated structure of an adhesives resin ingredient accompanying oxidation reaction as shown in FIG. 4 does not take place. And it is thought that the macromolecule formation with which the normal chain molecule became entangled as shown in FIG. 3 has occurred actively. The hue of resin is still the light yellow of B stage as the proof, and increases of electron transition absorption are hardly observed. Therefore, since sufficient crosslinkage structure is not formed in the inside of resin, a solubility parameter cannot fully change, and low molecular compounds 1c, such as methanol, cannot be pressed out from the inside of resin.
As shown in FIG. 5, a Cu lead frame with a fixed tape shown in Step S1 is prepared first. That is, as shown in lead frame preparation of FIGS. 8 and 12, along with inner lead 3a sequence, lead frame 3 on which tape 1 of the shape of a square ring was stuck on inner lead 3a is prepared. In the lead frame 3, a tab 3c which is a chip mounting part, hanging leads 3d with which tab 3c is supported in the four corner parts, a plurality of inner leads 3a arranged around tab 3c and a plurality of outer leads 3b which lead to each inner lead 3a in one, respectively are formed.
Tape 1 prevents deformation of inner lead 3a etc. stopping the disturbance of inner lead 3a, and as shown in FIG. 7, tape 1 includes a layer of adhesives 1a, and a layer of base film 1b. Base film 1b is 50 micrometers in thickness, and is formed from polyimide etc., for example. Adhesives 1a are mixed adhesives which are 50 micrometers in thickness and make phenol resin and bismaleimide resin the main ingredients, for example. Adhesives 1a are also thermosetting adhesives, and low molecular compounds 1c (impurities), such as methanol, acetaldehyde, or acetone, are contained in these adhesives 1a.
Lead frame 3 includes copper or a copper alloy, for example. As shown in lead frame preparation of FIG. 12, silver plating 5 is formed at the tip of the surface of the surface side of each inner lead 3a, namely of the wire connection side.
Then, in the manufacturing method of the semiconductor device of this Embodiment 1, the frame baking shown in Step S2 of FIG. 5, i.e., the heat treatment to lead frame 3 with tape 1, is performed. In that case, lead frame 3 is heated, in the atmosphere which has oxygen, at the temperature of 180 to 300.degree. C., for a total of more than 2 minutes. For example, in the inside of oxygen environment, lead frame 3 is heated at the temperature of 240.degree. C. for 2 to 5 minutes.
Thereby, as shown in FIG. 1B of Embodiment 1, the hardening reaction accompanied by oxidization crosslinkage 1d in resin of adhesives 1a can be promoted. Crosslinkage density becoming high, low molecular compound 1c volatilizes and jumps out outside. That is, low molecular compound 1c can be pressed out outside from the inside of resin. As a result, since low molecular compound 1c leading to increase of the degree of ion migration does not remain in resin of adhesives 1a, movement of Cu ion between leads can be lost, therefore the generation of Cu migration can be prevented.
Since, after wire bonding, an alloy layer is formed when this connected a gold ball, and a pad 4c of aluminum of a semiconductor chip 4, and, if heat is applied to this, the alloy layer is spread, and it may cut in reliability examination and may result in the generation of a defective unit, cutting by the alloy layer can be prevented by heat-treating (frame baking) before wire bonding.
Die bonding shown in Step S3 is performed after the end of heat treatment of Step S2 (frame baking) shown in FIG. 5. That is, as shown in die bonding of FIGS. 9 and 12, tab (part) 3c of lead frame 3, and a back 4b of semiconductor chip 4 are connected with silver paste (die-bonding material) 9.
Wire bonding shown in Step S4 of FIG. 5 is performed after die bonding. That is, as shown in the wire bonding of FIGS. 10 and 12, inner lead 3a of lead frame 3 and pad 4c of a main surface 4a of semiconductor chip 4 are electrically connected with a wire 7. Wire 7 is a gold wire, for example.
Since coating of the silver plating 5 is performed near the tip of the surface side of each inner lead 3a in that case, even if heat treatment of lead frame 3 with tape 1 (frame baking) was performed and inner lead 3a has oxidized, silver plating 5 portion at that tip has prevented oxidization, therefore can connect wire 7 to this silver plating 5 portion.
Then, plating shown in Step S7 of FIG. 5 is performed. Here, exterior plating of solder plating etc. is given to a plurality of outer leads 3b projected from sealed body 6.
Lead cut formation shown in Step S8 of FIG. 5 is performed after plating formation. Here, as shown in the cut formation of FIG. 13, cutting and formation of outer lead 3b are performed. That is, while performing cutting from lead frame 3 of each outer lead 3b, each outer lead 3b is bent and formed in the shape of a gull wing, and it becomes assembly completion of a QFP (Quad Flat Package) 2.
The semiconductor device of the modification shown in FIGS. 14 and 15 is a heat radiation type QFP 8, and is a semiconductor device of the structure where laminated tape member 10 was stuck at the tip of the back side of each inner lead 3a (the surface of the opposite side against the surface which connects wire 7) via adhesives 1a.
Since, also in the case of this heat radiation type QFP 8, the defect by copper migration will occur if each lead which includes inner lead 3a and outer lead 3b is formed of copper or a copper alloy, and low molecular compounds 1c (impurities), such as methanol, acetaldehyde, or acetone, are contained in resin of adhesives 1a, like the manufacturing method of the semiconductor device of this Embodiment 1, by heating lead frame 3 at the temperature of 160 to 300.degree. C. (preferably 180 to 300.degree. C.) for a total of more than 2 minutes in the atmosphere which has oxygen after sticking a tape member 10 on lead frame 3 and before performing a resin molding, the hardening reaction accompanied by oxidization crosslinkage 1d in resin of adhesives 1a can be promoted, low molecular compound 1c can be volatilized and taken out outside, and the generation of migration can be prevented.
The semiconductor device of the modification shown in FIGS. 16 and 17 is a TCP (Tape Carrier Package) 13, and is the semiconductor package in which semiconductor chip 4 is arranged in a device hole 1k mostly formed in the center of tape 1, and a plurality of leads of a copper foil 1e arranged around semiconductor chip 4 and pad 4c of semiconductor chip 4 are electrically connected by a bump 11, and to which the resin molding of semiconductor chip 4, bump 11, and the copper foil 1e is performed by sealing part 12.
In tape 1 of this TCP 13, the lead of copper foil 1e, a wiring part 1j which leads to the lead, and an inner lead 1g and an outer lead 1i which lead to wiring part 1j are provided, and inner lead 1g and outer lead 1i are connected to a test pad 1h. While copper foil 1e and wiring part 1j are stuck on tape 1 via adhesives 1a in that case, wiring part 1j is covered with and insulated by an insulating solder regist 1f.
A plurality of sprocket holes 1m are formed in the both-sides part of the width direction of tape 1 along with regular intervals. The region inside a plurality of test pads 1h provided in both sides serves as a user's area 1n.
Also in this TCP 13, if wiring part 1j, inner lead 1g, and outer lead 1i are formed of copper or a copper alloy, and low molecular compounds 1c (impurities), such as methanol, acetaldehyde, or acetone, are contained in resin of adhesives 1a, the defect by copper migration will occur. Therefore, by heating, after connecting copper foil 1e, wiring part 1j, and tape 1 via adhesives 1a and before performing a resin molding, like the manufacturing method of the semiconductor device of this Embodiment 1, at the temperature of 160 to 300.degree. C. (preferably 180 to 300.degree. C.) for a total of more than 2 minutes in the atmosphere which has oxygen, the hardening reaction accompanied by oxidization crosslinkage 1d in resin of adhesives 1a can be promoted, low molecular compound 1c can be volatilized and taken out outside, and the generation of copper migration can be prevented.
As a result, improvement in the reliability of TCP 13 can be aimed at. Adopting the flexible wiring board which stuck the wiring pattern (conductor part) which includes copper or a copper alloy via thermosetting adhesives on a substrate, and applying the manufacturing method of the semiconductor device of this Embodiment 1 also when using this flexible wiring board in the assembling process of a semiconductor device, by heating at the temperature of 160 to 300.degree. C. (preferably 180 to 300.degree. C.) for a total of more than 2 minutes in the atmosphere which has oxygen before performing a resin molding, the generation of copper migration can be prevented.
First, as shown in Step S21 of FIG. 18, lead frame 3 is manufactured. That is, a lead pattern is formed by press processing or etching processing, and lead frame 3 which is shown in FIG. 19 and which has a plurality of leads (inner lead 3a and outer lead 3b) is formed. Lead frame 3 is formed of copper or a copper alloy.
Then, as shown in FIG. 20, the partial silver plating step which gives silver plating 5 at the tip of each inner lead 3a is performed. After that, the taping step shown in FIG. 21 is performed. That is, tape 1 is stuck at lead frame 3 about which silver plating 5 is given at the tip of each inner lead 3a, via adhesives 1a containing low molecular compound 1c (refer to FIG. 1). For example, tape 1 formed in the shape of a square ring is stuck on each inner lead 3a along an inner lead sequence. Adhesives 1a are thermosetting adhesives.
Then, frame baking shown in Step S22 of FIG. 18 is performed. That is, in the atmosphere which has oxygen, lead frame 3 is heated at the temperature of 160 to 300.degree. C. (preferably 180 to 300.degree. C.) for a total of more than 2 minutes.
For example, although the Embodiments 1 and 2 explained the case of acetaldehyde, methanol, or acetone as low molecular compound 1c (impurities) volatilized from resin of adhesives 1a by heating, low molecular compound 1c may not be limited to these substances, and as long as it is low molecular compound 1c contained in resin of adhesives 1a, they may be other substances.
Although the Embodiments 1 and 2 explained the case where phenol resin and bismaleimide resin were the main ingredients, in adhesives 1a, resin used as the main ingredients of adhesives 1a may be other resin.
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