Process for etching a semiconductor lead frame

• US 5,683,943 A
• Filed: 06/12/1995
• Issued: 11/04/1997
• Est. Priority Date: 06/14/1994
• Status: Expired due to Term

• Current Assignee: Dai Nippon Printing Company Limited
• Original Assignee: Dai Nippon Printing Company Limited
• Inventors: Yamada, Junichi
• Primary Examiner(s): GRAYBILL, DAVID E
• Application Number:
  US08/489,319
• Time in Patent Office: 876 Days
• Field of Search: 29/827, 437/220, 156/651, 257/671, 257/672, 257/670
• US Class Current: 216/14
• CPC Class Codes: H01L 21/4828 Etching etching for cleaning without patterning H01L21/4835
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 23/49548 Cross section geometry H01L23/49562 takes precedence
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 2924/00012 Relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/00015 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed as prior art
• CPC Class Codes: H01L 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: Y10T 29/49121 Beam lead frame or beam lead device

Abstract

A method for producing a lead frame having outer leads and inner leads, for use in constructing a resin-sealed semiconductor package comprises etching processes for etching a blank. A first resist pattern having a first opening and a second resist pattern having second openings are formed on the first and the second major surfaces of a blank. The first and the second major surfaces of the blank are etched through the first and the second resist pattern by a first etching process using a first etchant to form a first recess corresponding to the first opening and second recesses corresponding to the second recesses in the first and the second major surfaces, respectively. The first recess is filled up with an etch-resistant layer. The second major surface is etched through the second resist pattern by a second etching process using a second etchant so that portions of the blank corresponding to the second openings of the second resist pattern are etched through to form the tips of the inner leads.

Claims

1. A method for producing a lead frame having a plurality of outer leads and a plurality of inner leads respectively having tips, for a resin-sealed semiconductor package, comprising:

coating a first and a second major surface of a blank for a lead frame with a first and a second photoresist layer, respectively;

forming a first resist pattern having a first opening on the first major surface of the blank by exposing the first photoresist layer through a first pattern mask and a second resist pattern having second openings on the second major surface of the blank by exposing the second photoresist layer through a second pattern mask;

applying a first etchant to at least the first major surface of the blank to form an etched recess;

cleaning the surface of the etched recess formed in the first major surface of the blank after applying the first etchant;

pickling the cleaned surface of the etched recess to remove oxides and hydroxides tarnishing the surface of the etched surface;

forming a protective film over the pickled surface of the etched recess to prevent oxidation and hydraulic;

forming an etch-resistant layer of an etch-resistant material to fill the etched recess in the first major surface of the blank;

applying a second etchant to the second major surface of the blank to etch through remaining portions of the blank; and

removing the etch resistant layer, the first resist pattern and the second resist pattern from the resulting lead frame and cleaning the lead frame.

2. The method for producing a lead frame according to claim 1, wherein the first opening of the first resist pattern exposes an area on the first major surface of the blank in which the tips of the inner leads of the lead frame are to be formed, and the second openings of the second resist pattern expose areas on the second major surface of the blank to form the tips of the inner leads of the lead frame.

3. The method for producing a lead frame according to claim 1, wherein the blank comprises a 42% Ni/Fe alloy, and the first etchant comprises a ferric chloride aqueous solution at a temperature of at least 55°

C. and of a ferric chloride concentration of at least 47 Be.

4. The method for producing a lead frame, according to claim 1, wherein

the depth of the etched recess formed in the first major surface of the blank is 1/2 to 4/5 of the thickness of the blank.

5. The method for producing a lead frame, according to claim 1, wherein

the protective film is formed by immersing the blank in a 0.5 to 20% wt. benzotriazole aqueous solution or by spraying the 0.5 to 20% wt. benzotriazole aqueous solution over the pickled surface of the etched recess.

6. The method for producing a lead frame according to claim 1, further comprising:

cleaning both major surfaces of the blank after removing the resist pattern;

pickling both cleaned major surfaces of the blank to remove oxides and hydroxides on the surface of the blank; and

forming a protective film over the major surface of the blank to prevent oxidation and hydration.

7. The method for fabricating a lead frame, according to claim 6, wherein

the protective film is formed by immersing the blank in a 0.2 to 20% wt. benzotriazole aqueous solution or by spraying 0.2 to 20% wt. benzotriazole aqueous solution over the major surfaces of the blank.