Method of forming an electronic package with a solder seal

• US 6,352,195 B1
• Filed: 09/18/2000
• Issued: 03/05/2002
• Est. Priority Date: 12/20/1996
• Status: Expired due to Fees

• Current Assignee: RF Monolithics, Inc. (Murata Manufacturing Co Limited)
• Original Assignee: RF Monolithics, Inc. (Murata Manufacturing Co Limited)
• Inventors: Johnson, Paul O., Guthrie, Frank E.
• Primary Examiner(s): ELVE, MARIA ALEXANDRA
• Application Number:
  US09/664,198
• Time in Patent Office: 533 Days
• Field of Search: 228/123.1, 228/124.6, 228/56.3, 228/245, 228/214, 228/219, 228/220, 228/234.2
• US Class Current: 228/123.1
• CPC Class Codes: B23K 1/008 Soldering within a furnace B23K1/012 takes precedence
• CPC Class Codes: H01L 23/10 characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• 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 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]

Abstract

A method of attaching a lid with at least a metallic surface thereon to a substrate to enclose a surface acoustic wave electronic circuit using a fluxless solder preform having an undesired oxide surface and associated with the metallic surface on the lid and in superimposed and abutting relationship with a gold seal ring surrounding the electronic circuit to form a unit that is heated in a furnace having a hydrogen atmosphere such that the hydrogen removes any undesired oxide surfaces from the solder preform and the metallic surface on the lid by combining with the oxygen therein to form moisture so as to remove any oxide surfaces from the solder preform and the lid metallic surface and enable a complete bonding of the fluxless solder preform with the gold seal ring and the lid metallic surface thereby forming a hermetically sealed package.

Claims

1. A method of forming separable SAW circuit packages comprising the steps of:

forming a predetermined pattern of SAW circuits on a substrate wherein each of said SAW circuits comprises a solderable seal ring;

arranging a corresponding predetermined pattern of solderable lids in a lid fixture wherein each of said solderable lids comprises a solderable peripheral flange;

providing like solder preforms for mating with corresponding ones of said solderable seal rings and said solderable peripheral lid flange; and

heating said substrate and said lid fixture in a furnace having a reducing atmosphere until any undesired oxide layer in said solder preforms, seal rings, and solderable lid flanges combine with said reducing atmosphere to create substantially oxide-free bonding surfaces wherein said solder bonds to said solderable seal ring and solderable lid to sealingly attach said solderable lids with corresponding ones of said SAW circuits on said substrate.

2. The method as recited in claim 1 further comprising the step of attaching each of said solder preforms to said periphery of a corresponding one of said lids in a fixed relationship.

3. The method as recited in claim 1 further comprising the step of heating said substrate and said lid fixture in said furnace in a hydrogen reducing atmosphere to form said oxide-free bonding surfaces.

4. The method as recited in claim 1 further comprising the step of electrically connecting a ground terminal on each of said SAW circuits to a corresponding one of said solderable seal rings such that when said lid is soldered to said solderable seal ring, a Faraday shielded package is formed.

5. The method as recited in claim 3 further comprising the step of heating said superimposed substrate and said lid fixture in said furnace at 385°

±

20°

C. for 10±

6 minutes to react said hydrogen with said oxygen in said undesired oxide surfaces according to the equation

6. The method as recited in claim 5 further comprising the step of melting said heated solder to form a hermetically sealed package with said solderable seal ring and solderable lid.

7. The method as recited in claim 1 further comprising the step of forming said solderable seal ring from gold alloy.

8. The method as recited in claim 3 further comprising the step of forming said hydrogen atmosphere of a minimum of 10% hydrogen and 90% nitrogen.

9. A SAW circuit package formed in accordance with the method set forth in claim 1.

10. A method of hermetically enclosing a SAW circuit comprising the steps of:

forming a SAW circuit on a ceramic substrate, said SAW circuit surrounded with a gold seal ring;

associating a fluxless solder preform with a solderable lid for covering said SAW circuit;

mating said solderable lid and said SAW circuit with said fluxless solder preform in superimposed abutting relationship with said gold seal ring to form an electronic circuit package; and

heating said electronic circuit package in a furnace having a reducing atmosphere until any undesired oxide coatings in said fluxless solder preform, said gold seal rings, and said solderable lid combine with said reducing atmosphere to create substantially oxide-free bonding surfaces, wherein said solder melts and attaches to said gold seal ring to sealingly attach said solderable lid to said ceramic substrate to form a hermetically sealed electronic circuit package.

11. The method as recited in claim 10 further comprising the step of attaching said fluxless solder preform to said solderable lid in a fixed relationship prior to placing said solderable lid on said ceramic substrate.

12. The method as recited in claim 10 further comprising the step of heating said electronic circuit package in said furnace in a hydrogen atmosphere.

13. The method as recited in claim 10 further comprising the step of forming said solderable lid entirely of metal.

14. The method as recited in claim 13 further comprising the step of electrically connecting a ground terminal on said SAW circuit to said gold seal ring such that when said solderable lid is soldered to said gold seal ring forming a Faraday shield for said circuit package.

15. The method as recited in claim 12 further comprising the step of heating said circuit package in said furnace at 385°

±

20°

C. for 10±

6 minutes to react said hydrogen with oxygen in said undesirable oxide according to the equation

16. The method as recited in claim 10, further comprising the steps of:

forming said solderable lid of a non-metallic material having a solderable ring on a peripheral flange making said lid a solderable lid; and

attaching each of said fluxless solder preforms to said peripheral flange of said lid.

17. The method as recited in claim 10 wherein said step of heating comprises the step of heating said ceramic substrate and said lid fixture to a temperature greater than approximately 350°

C.

18. A SAW circuit hermetically sealed in accordance with the method set forth in claim 10.

19. A method of hermetically enclosing a SAW circuit comprising the steps of:

forming a SAW circuit on a ceramic substrate having a gold seal ring on said ceramic substrate;

associating a fluxless solder preform with a solderable lid used to cover said SAW circuit wherein at least said fluxless solder preform has an undesired oxide coating thereon;

placing said solderable lid over said SAW circuit with said solder preform in superimposed abutting relationship with said gold seal ring to form an electronic circuit package; and

heating said electronic circuit package in a furnace having a reducing atmosphere to a temperature greater than approximately 350°

C. until any undesired oxide coatings combine with said reducing atmosphere to create substantially oxide-free bonding surfaces, said solder melting and attaching to said gold seal ring to sealingly attach said solderable lid to said substrate and form a hermetically sealed electronic circuit package.

20. A SAW circuit hermetically sealed in accordance with the method set forth in claim 19.

21. A method of forming separable SAW circuit packages comprising the steps of:

forming a pattern of SAW circuits on a substrate wherein each of said SAW circuits comprises a solderable seal ring;

arranging a pattern of solderable lids in a lid fixture wherein each of said solderable lids comprises a solderable peripheral flange;

providing like solder preforms for mating with corresponding ones of said solderable seal rings and said solderable peripheral lid flange; and

heating said substrate and said lid fixture in a furnace having a reducing atmosphere until any undesired oxide layer in said solder preforms, seal rings, and solderable lid flanges combine with said reducing atmosphere to create substantially oxide-free bonding surfaces wherein said solder bonds to said solderable seal ring and solderable lid to sealingly attach said solderable lids with corresponding ones of said SAW circuits on said substrate.