Method of assembling a semiconductor device using a magnet

• US 5,834,320 A
• Filed: 09/23/1997
• Issued: 11/10/1998
• Est. Priority Date: 06/05/1995
• Status: Expired due to Fees

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Huddleston, Wyatt A., Szewczyk, Andrew
• Primary Examiner(s): GRAYBILL, DAVID E
• Application Number:
  US08/935,976
• Time in Patent Office: 413 Days
• Field of Search: 437/212, 437/213, 437/216, 437/217, 437/220, 438/3, 438/373, 438/383, 438/119, 438/123, 438/760
• US Class Current: 438/3
• CPC Class Codes: H01L 21/50 Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/32225 the item being non-metallic, e.g. insulating substrate with or without metallisation
• CPC Class Codes: H01L 2224/45015 being circular
• CPC Class Codes: H01L 2224/45099 Material
• 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 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2224/85399 Material
• 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 24/48 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 2924/01039 Yttrium [Y]
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/15153 the die mounting substrate comprising a recess for hosting the device
• CPC Class Codes: H01L 2924/15165 Monolayer substrate
• CPC Class Codes: H01L 2924/16152 Cap comprising a cavity for hosting the device, e.g. U-shaped cap
• CPC Class Codes: H01L 2924/207 Diameter ranges

Abstract

Process for maintaining lead positions within a glass layer of a CQFP semiconductor device by using a magnet during high temperature assembly operations. During lead embed, a magnet (46) is magnetically attached to lead frame (44). Upon reflow of a glass layer (48), leads (50) sink into the glass layer to a height controlled by the height (H) of a protrusion (52) of the magnet. A similar magnet (62) can be used to maintain the lead positions during a high temperature operation used to cure a die attach material (60). Yet another magnet (70) can be used to maintain the positions of leads (50) during a lid seal operation. A common magnet design for use in all thermal operations can instead be used. Use of the magnets restrict movement of the leads within the glass layer when the glass is in a softened state.

Claims

1. A method of assembling a semiconductor device comprising the steps of:

providing a base having a reflowable material on a surface thereof, the reflowable material being glass and has a reflow temperature, and the base being a ceramic base;

providing a lead frame capable of being magnetized and having a plurality of leads, wherein the lead frame is positioned on the surface of the base;

placing a magnet on the lead frame;

subjecting the base, the lead frame, and the magnet to a thermal process involving a temperature of at least the reflow temperature of the reflowable material, wherein during the step of subjecting, the magnet restricts movement of the plurality of leads, thereby maintaining accurate positions of the plurality of leads within the reflowable material; and

removing the magnet from the lead frame after the step of subjecting.

2. The method of claim 1 wherein the step of providing a lead frame comprises providing a lead frame made of an alloy of iron and nickel.

3. The method of claim 1 wherein the step of placing a magnet comprises placing a magnet comprised of an alloy of aluminum, nickel, and cobalt.

4. The method of claim 1 wherein the step of placing a magnet comprises aligning the magnet to the lead frame using an alignment member incorporated into the magnet.

5. The method of claim 1 wherein the step of subjecting comprises subjecting the base, the lead frame, and the magnet to a temperature of at least 350°

C.

6. A method of assembling a semiconductor device comprising the steps of:

providing a package base having a glass layer formed on a surface thereof;

providing a magnetizable lead frame having a plurality of leads;

providing a magnet;

positioning the magnetizable lead frame on the package base such that the plurality of leads is next to the glass layer;

placing the magnet on the magnetizable lead frame; and

embedding the plurality of leads into the glass layer by subjecting the package base, the magnetizable lead frame, and the magnet to a thermal operation involving a temperature above a reflow temperature of the glass layer, wherein during the thermal operation the magnet restricts movement of the plurality of leads to control positions of the plurality of leads within the glass layer.

7. The method of claim 6 wherein the step of providing a package base comprises providing a package base having a cavity, and wherein the step of providing a magnet comprises providing a magnet having a protrusion, and wherein the step of placing the magnet comprises placing the magnet on the magnetizable lead frame and over the package base such that the protrusion of the magnet fits within the cavity of package base.

8. The method of claim 7 wherein the step of providing a magnet comprises providing a magnet wherein the protrusion has a stand off height equal to a depth of the cavity plus a desired embedded lead height as measured from the surface of the package base.

9. The method of claim 6 wherein the step of embedding comprises embedding the plurality of leads by softening the glass layer in the thermal operation and relying upon a weight of the magnetizable lead frame and a weight of the magnet to push the plurality of leads into the glass layer upon softening.

10. The method of claim 6 wherein during the step of embedding, the package base, the magnetizable lead frame, and the magnet are subjected to a temperature of at least 350°

C.

11. A method of assembling a semiconductor device comprising the steps of:

providing a package base having a die receiving area and a glass layer surrounding the die receiving area, the glass layer having a reflow temperature;

providing a lead frame capable of being magnetized and having a plurality of leads;

providing a semiconductor die;

providing a magnet;

embedding the plurality of leads into the glass layer of the package base;

attaching the semiconductor die to the die receiving area of the package base using a die attach material; and

curing the die attach material by subjecting the package base, the lead frame, and the semiconductor die to a thermal process involving a temperature in excess of the reflow temperature of the glass layer;

wherein during the step of curing, the magnet is brought into contact with the lead frame to maintain positions of the plurality of leads during the thermal process.

12. The method of claim 11 wherein the step of attaching comprises attaching the semiconductor die using a silver-filled die attach material.

13. The method of claim 11 wherein the step of embedding comprises using a magnet to maintain positions of the plurality of leads during the step of embedding.

14. The method of claim 11 wherein the step of providing a magnet comprises providing a magnet which includes a cavity, and wherein the semiconductor die fits within the cavity when the magnet is brought into contact with the lead frame.

15. The method of claim 11 wherein during the step of curing, the package base, the lead frame, and the semiconductor die are subjected to a temperature of at least 350°

C.

16. A method of assembling a semiconductor device comprising the steps of:

providing a package base having a periphery, a die receiving area, a semiconductor die mounted in the die receiving area, and a lead frame having a plurality of leads positioned around the semiconductor die, wherein a portion of each lead of the plurality of leads extends beyond the periphery of the package base;

providing a lid having a periphery and a glass layer at least around the periphery of the lid, the glass layer having a reflow temperature;

placing the lid over the package base such that the semiconductor die is enclosed, such that the glass layer of the lid is in contact with the plurality of leads, and such that at least a portion of each lead of the plurality of leads extends beyond the periphery of the lid; and

sealing the lid and the package base together by subjecting the lid and package base to a thermal process involving a temperature in excess of the reflow temperature of the glass layer;

wherein during the step of sealing, a magnet is magnetically attached to those portions of each lead of the plurality of leads which extend beyond the periphery of the lid and beyond the periphery of the package base to maintain positions of the plurality of leads during the thermal process.

17. The method of claim 16 wherein the step of providing a package base comprises providing a ceramic package base and wherein the step of providing a lid comprises providing a ceramic lid.

18. The method of claim 16 wherein the step of sealing comprises subjecting the package base to a temperature of at least 350°

C.

19. A method of assembling a semiconductor device comprising the steps of:

providing a ceramic base having a reflowable material on a surface thereof, the reflowable material having a reflow temperature;

providing a lead frame capable of being magnetized and having a plurality of leads, wherein the lead frame is positioned on the surface of the base;

placing a magnet in contact with the lead frame; and

subjecting the base, the lead frame, and the magnet to a thermal process involving a temperature of at least the reflow temperature of the reflowable material, wherein during the step of subjecting, the magnet restricts movement of the plurality of leads, thereby maintaining accurate positions of the plurality of leads within the reflowable material.

20. A method of assembling a semiconductor device comprising the steps of:

providing a base having a glass reflowable material on a surface thereof, the reflowable material having a reflow temperature;

providing a lead frame capable of being magnetized and having a plurality of leads, wherein the lead frame is positioned on the surface of the base;

placing a magnet on the lead frame; and

subjecting the base, the lead frame, and the magnet to a thermal process involving a temperature of at least the reflow temperature of the reflowable material, wherein during the step of subjecting, a magnetic field of the magnet restricts movement of the plurality of leads, thereby maintaining accurate positions of the plurality of leads within the reflowable material.

21. A method of assembling a semiconductor device comprising the steps of:

providing a base having a reflowable material on a surface thereof, the reflowable material having a reflow temperature;

placing a semiconductor substrate onto the base;

providing a lead frame capable of being magnetized and having a plurality of leads, wherein the lead frame is positioned on the surface of the base;

placing a magnet on the lead frame;

subjecting the base, the lead frame, and the magnet to a thermal process involving a temperature of at least the reflow temperature of the reflowable material, wherein during the step of subjecting, the magnet restricts movement of the plurality of leads, thereby maintaining accurate positions of the plurality of leads within the reflowable material; and

removing the magnet from the lead frame after the step of subjecting.

22. A method of assembling a semiconductor device comprising the steps of:

providing a base having a reflowable material on a surface thereof, the reflowable material having a reflow temperature;

placing a semiconductor substrate onto the base;

providing a lead frame capable of being magnetized and having a plurality of leads, wherein the lead frame is positioned on the surface of the base;

placing a magnet on the lead frame;

subjecting the base, the lead frame, and the magnet to a thermal process involving a temperature of at least the reflow temperature of the reflowable material, and

removing the magnet from the lead frame after the step of subjecting.