LEADFRAME TREATMENT FOR ENHANCING ADHESION OF ENCAPSULANT THERETO

• US 20080216921A1
• Filed: 03/07/2007
• Published: 09/11/2008
• Est. Priority Date: 03/07/2007
• Status: Active Grant

• Current Assignee: Advanced Assembly Materials International Limited
• Original Assignee: ASM Assembly Materials Ltd. (ASMPT Ltd.)
• Inventors: LEE, Chi Chung, KWAN, Yiu Fai, CHAN, Tat Chi, CHAN, Wai
• Granted Patent: US 8,012,886 B2
• Time in Patent Office: Days
• US Class Current: 148/95
• CPC Class Codes: C22C 1/00 Making non-ferrous alloys by electrothermic methods C22B4/00; by electrolysis C25C1/24, C25C3/36
• CPC Class Codes: H01L 21/4821 Flat leads, e.g. lead frames with or without insulating supports
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/45147 Copper (Cu) as principal constituent
• CPC Class Codes: H01L 2224/48 of an individual wire connector
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48639 Silver (Ag) as principal constituent
• CPC Class Codes: H01L 2224/48655 Nickel (Ni) as principal constituent
• CPC Class Codes: H01L 2224/48664 Palladium (Pd) as principal constituent
• CPC Class Codes: H01L 2224/48839 Silver (Ag) as principal constituent
• CPC Class Codes: H01L 2224/48855 Nickel (Ni) as principal constituent
• CPC Class Codes: H01L 2224/48864 Palladium (Pd) as principal constituent
• CPC Class Codes: H01L 2224/85011 Chemical cleaning, e.g. etching, flux
• CPC Class Codes: H01L 2224/85439 Silver (Ag) as principal constituent
• CPC Class Codes: H01L 2224/85455 Nickel (Ni) as principal constituent
• CPC Class Codes: H01L 2224/85464 Palladium (Pd) as principal constituent
• CPC Class Codes: H01L 23/49582 Metallic layers on lead frames
• CPC Class Codes: H01L 23/49586 Insulating layers on lead frames
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• 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 2924/01028 : Nickel [Ni]
• CPC Class Codes: H01L 2924/01047 : Silver [Ag]
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/15747 : Copper [Cu] as principal constituent
• CPC Class Codes: Y10S 438/909 : Controlled atmosphere
• CPC Class Codes: Y10S 438/974 : Substrate surface preparation

Abstract

A method is provided for treating a leadframe comprising copper or copper alloy to enhance adhesion of molding compound to it. The leadframe is oxidized in an oxidation treatment bath to form copper oxide on the surface of the leadframe. It is then dipped in a complexing or chelating agent to enhance the purity of the copper oxide formed. Thereafter, the leadframe is cleaned with an acid to remove any contaminants remaining on the leadframe.

Claims

1. A method for treating a leadframe to enhance adhesion of molding compound to the leadframe, the method comprising the steps of:

providing the leadframe comprising copper or copper alloy and having a surface;

oxidizing the leadframe in an oxidation treatment bath to form copper oxide on the surface of the leadframe;

dipping the leadframe in a complexing or chelating agent to enhance the purity of the copper oxide formed; and

thereafter

cleaning the leadframe with an acid to remove contaminants remaining on the leadframe.

2. The method for treating a leadframe as claimed in claim 1, wherein the oxidation bath comprises an oxidizing agent, a topography modifier and an organic additive.

3. The method for treating a leadframe as claimed in claim 2, wherein the oxidizing agent comprises one or more compounds selected from the group consisting of:

hydrogen peroxide, sodium persulfate and sodium chlorite.

4. The method for treating a leadframe as claimed in claim 2, wherein the topography modifier comprises one or more compounds selected from the group consisting of:

a triazle, a tetrazole and an imidoazole.

5. The method for treating a leadframe as claimed in claim 2, wherein the organic additive comprises an amine or quaternary ammonium salt.

6. The method for treating a leadframe as claimed in claim 1, further comprising the step of, prior to oxidizing the leadframe, immersing the leadframe in an oxidation pre-dip comprising a topography modifier and an organic additive but without an oxidizing agent.

7. The method for treating a leadframe as claimed in claim 1, wherein the thickness of the copper oxide formed is in the range of 50 Å

to 500 Å

.

8. The method for treating a leadframe as claimed in claim 1, wherein the complexing or chelating agent comprises a nitrogen, oxygen or sulfur-containing compound.

9. The method for treating a leadframe as claimed in claim 8, wherein the complexing or chelating agent comprises one or more compounds selected from the group consisting of:

ammonia, amino acid and an ammonium salt.

10. The method for treating a leadframe as claimed in claim 8, wherein the complexing or chelating agent comprises one or more compounds having a carboxylic group or a hydroxyl group.

11. The method for treating a leadframe as claimed in claim 8, wherein the complexing or chelating agent comprises one or more compounds selected from the group consisting of:

thiosulfate, thiocyanate, mercaptan and mercaptocarboxylic acid.

12. The method for treating a leadframe as claimed in claim 1, further comprising the step of applying ultrasonic, spraying, heating or compressed air when dipping the leadframe in the complexing or chelating agent.

13. The method for treating a leadframe as claimed in claim 1, wherein the concentration of the complexing or chelating agent in a dipping bath is 1-10%.

14. The method for treating a leadframe as claimed in claim 1, wherein the acid used for cleaning the leadframe comprises one or more acids selected from the group consisting of:

a mineral acid, sulfuric acid, hydrochloric acid, phosphorous acid and nitric acid.

15. The method for treating a leadframe as claimed in claim 14, wherein the concentration of acid in a chemical bath used for cleaning the leadframe is 1-10%.

16. The method for treating a leadframe as claimed in claim 1, wherein the copper oxide formed on the leadframe after treatment comprises a layer of copper oxide on fibrillar structures formed on the surface of the leadframe, the fibrillar structures having irregular crystalline formations and dendrites branching out from the said crystalline formations.

17. The method for treating a leadframe as claimed in claim 1, wherein the leadframe that is provided prior to the oxidizing has been selectively plated with silver plating over some areas of the leadframe.