EP0495005A1 - Die attach structure - Google Patents

Die attach structure

Info

Publication number
EP0495005A1
EP0495005A1 EP19900916935 EP90916935A EP0495005A1 EP 0495005 A1 EP0495005 A1 EP 0495005A1 EP 19900916935 EP19900916935 EP 19900916935 EP 90916935 A EP90916935 A EP 90916935A EP 0495005 A1 EP0495005 A1 EP 0495005A1
Authority
EP
European Patent Office
Prior art keywords
die
substrate
die attach
central portion
joint
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19900916935
Other languages
German (de)
French (fr)
Inventor
William Riis Hamburgen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Digital Equipment Corp
Original Assignee
Digital Equipment Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Digital Equipment Corp filed Critical Digital Equipment Corp
Publication of EP0495005A1 publication Critical patent/EP0495005A1/en
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01L24/00—Arrangements for connecting or disconnecting semiconductor or solid-state bodies; Methods or apparatus related thereto
    • H01L24/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
    • H01L24/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L24/31—Structure, shape, material or disposition of the layer connectors after the connecting process
    • H01L24/32—Structure, shape, material or disposition of the layer connectors after the connecting process of an individual layer connector
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    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/12—Mountings, e.g. non-detachable insulating substrates
    • H01L23/13—Mountings, e.g. non-detachable insulating substrates characterised by the shape
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    • H01L23/00—Details of semiconductor or other solid state devices
    • H01L23/48—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor
    • H01L23/488—Arrangements for conducting electric current to or from the solid state body in operation, e.g. leads, terminal arrangements ; Selection of materials therefor consisting of soldered or bonded constructions
    • H01L23/492—Bases or plates or solder therefor
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    • H01L24/80—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected
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    • H01L2224/26—Layer connectors, e.g. plate connectors, solder or adhesive layers; Manufacturing methods related thereto
    • H01L2224/2612—Auxiliary members for layer connectors, e.g. spacers
    • H01L2224/26152—Auxiliary members for layer connectors, e.g. spacers being formed on an item to be connected not being a semiconductor or solid-state body
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    • H01L2224/27013—Involving a permanent auxiliary member, i.e. a member which is left at least partly in the finished device, e.g. coating, dummy feature for holding or confining the layer connector, e.g. solder flow barrier
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    • H01L2224/31—Structure, shape, material or disposition of the layer connectors after the connecting process
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    • H01L2224/83009—Pre-treatment of the layer connector or the bonding area
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    • H01L2224/8312—Aligning
    • H01L2224/83136—Aligning involving guiding structures, e.g. spacers or supporting members
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    • H01L2224/83—Methods for connecting semiconductor or other solid state bodies using means for bonding being attached to, or being formed on, the surface to be connected using a layer connector
    • H01L2224/8319—Arrangement of the layer connectors prior to mounting
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    • H01L2224/8338—Bonding interfaces outside the semiconductor or solid-state body
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    • H01L2224/838—Bonding techniques
    • H01L2224/8385—Bonding techniques using a polymer adhesive, e.g. an adhesive based on silicone, epoxy, polyimide, polyester
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    • H01L2924/15786—Material with a principal constituent of the material being a non metallic, non metalloid inorganic material
    • H01L2924/15787—Ceramics, e.g. crystalline carbides, nitrides or oxides

Definitions

  • This invention pertains generally to semiconductor devices and, more particularly to a structure and method for attaching a semiconductor die to a substrate.
  • both the transfer of heat between the die and the substrate and the level of stress in the joint are dependent upon the thickness of the joint, with a thinner joint providing better heat transfer but higher stress.
  • the thickness of the joint represents a compromise between adequate heat transfer and an acceptable level of stress. This is difficult to realize in practice, particularly with large, high powered chips.
  • the invention provides an improved die attach structure and method in which the joint between the die and the substrate is formed in a manner which provides a more uniform temperature distribution in the die and reduces stress in the joint near the edge of the die.
  • the substrate is for ed with a non-planar surface in the die attach area, and the joint between the die and the substrate is thicker toward the edge of die than at the center.
  • different die attach materials are employed to make the joint stiffer toward the center of the die and more flexible toward the edges.
  • both the thickened joint and the different die attach materials are employed.
  • Figure 1 is an enlarged fragmentary sectional view of one embodiment of a die attach structure according to the invention.
  • Figures 2-4 are views similar to Figure 1 of additional embodiments of a die attach structure according to the invention.
  • the invention is illustrated in connection with a generally rectangular semiconductor die 11 and a generally planar substrate 12.
  • the die has a planar lower surface 13, and the substrate has a die attach area 14 in which the die is received.
  • the die attach area has a raised central portion 16 and a recessed outer portion 17, with the central portion of the die being positioned above the raised central portion of the die attach area and the edges of the die being positioned above the recessed portion of the area.
  • the die is bonded to the substrate by a die attach material 19 which fills the region between the lower surface of the die and the surface of the substrate in the die attach area, with a relatively thin joint 21 thus being formed beneath the central portion of the die and a thicker joint 22 being formed beneath the edge portions.
  • the raised portion of the die attach area has a planar surface 23, and the recessed portion of the area has a planar surface 24 which is positioned somewhat below the surface of the raised area.
  • the lower surface of the die is parallel to these surfaces.
  • the thinner joint at the center of the die provides better heat transfer between the die and the substrate in that area and results in a more uniform temperature across the die.
  • the thicker joint toward the edges of the die reduces stresses near the edges, although it may make the temperature of the die somewhat higher at the edges than it would be with a thinner joint.
  • the higher edge temperature is not a problem, however, and the peak die temperature is actually reduced because of the thinner joint at the center.
  • the embodiment of Figure 2 is generally similar to the embodiment of Figure 1, and like reference numerals designate corresponding elements in the two embodiments.
  • the edges 26 of the raised central portion of the die attach area are relieved or rounded, and the recessed portion of the area is formed with a concave surface 27. This contouring of the surfaces permits optimization of the temperature and/or stress distribution across the die.
  • the upper surface 31 of the central portion of the die attach area has a convex curvature, and the recessed portion has a concave curvature as in the embodiment of Figure 2.
  • This contouring of the surfaces permits optimization of the temperature and/or stress distribution over the entire surface of the die.
  • the embodiment of Figure 4 is generally similar to the embodiment of Figure 3, and like reference numerals once again designate corresponding elements.
  • the edge portions of the die extend beyond the recessed portion of the attach area, and the die is supported by the floor 33 of the attach area. This eliminates the need for a fixture or tooling to hold the die in a level position during assembly, but it does introduce a high stress concentration at the edges of the die.
  • the adhesive employed in this embodiment is selected to fail before the edge portions of the die break.
  • the thicker and thinner joints can be formed by configuring the lower surface of the die with a non-planar surface rather than forming the contoured mounting surface in the die attach area of the substrate.
  • the die and the substrate can both be formed with non-planar or contoured surfaces.
  • the die attach material which bonds the die to the substrate can be any suitable material for this purpose.
  • Such materials include solder, filled organic adhesives, glass/metal frits, and the like.
  • Improved temperature distribution and stress relief can also be provided by using different die attach materials for different portions of the die.
  • a relatively strong, stiff material can be employed in the central region where stress is minimal, with a weaker, more flexible material toward the edges where stress is greater.
  • the material employed in the center preferably has a high thermal conductivity, and the material employed at the edges can have a lower thermal conductivity.
  • Suitable materials include a high strength silver or diamond filled epoxy for the central region, and a modified low-modulus epoxy or a thermoplastic material for the outer region. As will be apparent to those familiar with the art, these are just a few examples of the numerous materials which can be used as the die attach materials.
  • the invention has a number of important features and advantages. It improves the joint between a die and a substrate and provides greater tolerance to mechanical stresses in the joint while providing good heat transfer across the joint. Making the joint thicker near the edge of the die than it is near the center reduces stresses near the edge of the die and allows greater heat transfer at the center. The use of a stronger, more thermally conductive die attach material at the center of the joint and a weaker, more flexible material toward the edges can also permit greater heat transfer toward the center and greater tolerance to stresses near the edges. Combining the tapered joint with different attach materials in different regions provides an even greater degree of control over temperature and stress distribution.

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  • Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Cooling Or The Like Of Semiconductors Or Solid State Devices (AREA)
  • Die Bonding (AREA)

Abstract

Structure et procédé de fixation de matrice dans lesquels la jointure entre une matrice (11) et un substrat (12) est formée de manière assurant une répartition de température uniforme dans la matrice, et réduisant la contrainte dans la jointure à proximité du bord de la matrice. Dans certains modes de réalisation, le substrat se compose d'une surface non plane dans la zone de fixation (14) de la matrice, et la jointure entre ladite matrice et ledit substrat est plus épaisse vers le bord de la matrice qu'au niveau du centre. Dans d'autres modes de réalisation, on emploie différents matériaux (19) de fixation de matrice afin de rendre la jointure plus dure vers le centre de la matrice, et plus souple vers les bords. Dans certains modes de réalisation, on emploie à la fois la jointure épaissie et les différents matériaux de fixation de matrice.A matrix fixing structure and method in which the joint between a matrix (11) and a substrate (12) is formed so as to provide a uniform temperature distribution in the matrix, and reducing stress in the joint near the edge of the matrix. In certain embodiments, the substrate consists of a non-planar surface in the fixing zone (14) of the matrix, and the joint between said matrix and said substrate is thicker towards the edge of the matrix than at the level of the Center. In other embodiments, different matrix fastening materials (19) are used to make the joint harder toward the center of the matrix, and more flexible toward the edges. In some embodiments, both the thickened joint and the various matrix attachment materials are used.

Description

DIE ATTACH STRUCTURE AND METHOD
This invention pertains generally to semiconductor devices and, more particularly to a structure and method for attaching a semiconductor die to a substrate.
Large, high powered semiconductor chips or dice are commonly mounted on metal or ceramic substrates which serve as heat sinks to carry heat away from the chips or dice. The conventional technique for attaching a die to a substrate involves joining a planar die to a planar substrate with a single material, typically a solder, an adhesive, or a fritted glass. If done properly, this results in a joint of uniform thickness.
One problem with this conventional technique is thermal spreading, or a tendency for the die to be hot near its center and cooler near it edges. This heating can limit the performance of the device and, in severe cases, result in damage τ_.o txie semiconductor.
Also, because of thermal gradients and a mismatch in coefficients of expansion between the die and the substrate, there is a stress in the joint. This stress is minimal near the center of the die and increases toward near the edges, and it can cause the joint to fail.
Both the transfer of heat between the die and the substrate and the level of stress in the joint are dependent upon the thickness of the joint, with a thinner joint providing better heat transfer but higher stress. In the conventional die attach, the thickness of the joint represents a compromise between adequate heat transfer and an acceptable level of stress. This is difficult to realize in practice, particularly with large, high powered chips.
The invention provides an improved die attach structure and method in which the joint between the die and the substrate is formed in a manner which provides a more uniform temperature distribution in the die and reduces stress in the joint near the edge of the die. In some embodiments, the substrate is for ed with a non-planar surface in the die attach area, and the joint between the die and the substrate is thicker toward the edge of die than at the center. In other embodiments, different die attach materials are employed to make the joint stiffer toward the center of the die and more flexible toward the edges. In some embodiments, both the thickened joint and the different die attach materials are employed.
Figure 1 is an enlarged fragmentary sectional view of one embodiment of a die attach structure according to the invention.
Figures 2-4 are views similar to Figure 1 of additional embodiments of a die attach structure according to the invention.
In Figure 1, the invention is illustrated in connection with a generally rectangular semiconductor die 11 and a generally planar substrate 12. The die has a planar lower surface 13, and the substrate has a die attach area 14 in which the die is received. The die attach area has a raised central portion 16 and a recessed outer portion 17, with the central portion of the die being positioned above the raised central portion of the die attach area and the edges of the die being positioned above the recessed portion of the area. The die is bonded to the substrate by a die attach material 19 which fills the region between the lower surface of the die and the surface of the substrate in the die attach area, with a relatively thin joint 21 thus being formed beneath the central portion of the die and a thicker joint 22 being formed beneath the edge portions.
The raised portion of the die attach area has a planar surface 23, and the recessed portion of the area has a planar surface 24 which is positioned somewhat below the surface of the raised area. The lower surface of the die is parallel to these surfaces.
The thinner joint at the center of the die provides better heat transfer between the die and the substrate in that area and results in a more uniform temperature across the die. The thicker joint toward the edges of the die reduces stresses near the edges, although it may make the temperature of the die somewhat higher at the edges than it would be with a thinner joint. The higher edge temperature is not a problem, however, and the peak die temperature is actually reduced because of the thinner joint at the center. The embodiment of Figure 2 is generally similar to the embodiment of Figure 1, and like reference numerals designate corresponding elements in the two embodiments. In the embodiment of Figure 2, however, the edges 26 of the raised central portion of the die attach area are relieved or rounded, and the recessed portion of the area is formed with a concave surface 27. This contouring of the surfaces permits optimization of the temperature and/or stress distribution across the die.
In the embodiment of Figure 3, the upper surface 31 of the central portion of the die attach area has a convex curvature, and the recessed portion has a concave curvature as in the embodiment of Figure 2. This contouring of the surfaces permits optimization of the temperature and/or stress distribution over the entire surface of the die.
The embodiment of Figure 4 is generally similar to the embodiment of Figure 3, and like reference numerals once again designate corresponding elements. In this embodiment, however, the edge portions of the die extend beyond the recessed portion of the attach area, and the die is supported by the floor 33 of the attach area. This eliminates the need for a fixture or tooling to hold the die in a level position during assembly, but it does introduce a high stress concentration at the edges of the die. To avoid breakage of the die, the adhesive employed in this embodiment is selected to fail before the edge portions of the die break.
If desired, the thicker and thinner joints can be formed by configuring the lower surface of the die with a non-planar surface rather than forming the contoured mounting surface in the die attach area of the substrate. Likewise, the die and the substrate can both be formed with non-planar or contoured surfaces.
The die attach material which bonds the die to the substrate can be any suitable material for this purpose. Such materials include solder, filled organic adhesives, glass/metal frits, and the like.
Improved temperature distribution and stress relief can also be provided by using different die attach materials for different portions of the die. Thus, for example, a relatively strong, stiff material can be employed in the central region where stress is minimal, with a weaker, more flexible material toward the edges where stress is greater. The material employed in the center preferably has a high thermal conductivity, and the material employed at the edges can have a lower thermal conductivity. Suitable materials include a high strength silver or diamond filled epoxy for the central region, and a modified low-modulus epoxy or a thermoplastic material for the outer region. As will be apparent to those familiar with the art, these are just a few examples of the numerous materials which can be used as the die attach materials.
When different materials are used for the central region and the outer region, it is not necessary to employ different joint thicknesses in the two regions, and the surfaces of both the die and the substrate can be planar. However, it is also possible to combine the two approaches and use a relatively strong, stiff material in for the thinner joint in the central region and a weaker, more flexible material for the thicker joint in the outer region.
The invention has a number of important features and advantages. It improves the joint between a die and a substrate and provides greater tolerance to mechanical stresses in the joint while providing good heat transfer across the joint. Making the joint thicker near the edge of the die than it is near the center reduces stresses near the edge of the die and allows greater heat transfer at the center. The use of a stronger, more thermally conductive die attach material at the center of the joint and a weaker, more flexible material toward the edges can also permit greater heat transfer toward the center and greater tolerance to stresses near the edges. Combining the tapered joint with different attach materials in different regions provides an even greater degree of control over temperature and stress distribution.
It is apparent from the foregoing that a new and improved die attach structure and method have been provided. While only certain presently preferred embodiments have been described in detail, as will be apparent to those familiar with the art, certain changes and modifications can be made without departing from the scope of the invention as defined by the following claims.

Claims

1. In a semiconductor device: a substrate having a die attach area with a mounting surface, a semiconductor die having a surface facing the mounting surface, one of said surfaces being contoured in such manner that a central portion of the die is closer to the substrate than an edge portion, a first die attach material filling the region between the central portion of the die and the substrate and bonding the central portion to the substrate, and a second die attach material filling the region between the edge portion of the die and the substrate and bonding the edge portion to the substrate.
2. The device of Claim 1 wherein the die attach area has a raised central portion and a recessed outer portion with surfaces which form the mounting surface.
3. The device of Claim 1 wherein the first die attach material is stiffer than the second die attach material.
4. The device of Claim 1 wherein the first die attach material has a higher thermal conductivity than the second die attach material.
5. In a semiconductor device: a substrate having a die attach area with a mounting surface, a semiconductor die having a surface facing the mounting surface, one of said surfaces being contoured in such manner that a central portion of the die is closer to the substrate than an edge portion, a die attach material filling the region between the die and the substrate and bonding the die to the substrate with a joint which is relatively thin toward the central portion of the die and thicker toward the edge portion.
6. The device of Claim 5 wherein the die attach area has a raised central portion and a recessed outer . portion with surfaces which form the mounting surface.
7. The device of Claim 6 wherein the surfaces of the central and outer portions of the die attach area are both generally planar.
8. The device of Claim 6 wherein the surface of the outer portion of the die attach area is concave.
9. The device of Claim 6 wherein the surface of the central portion of the die attach area is planar toward its middle and rounded toward its periphery.
10. The device of Claim 6 wherein the surface of the central portion of the die attach area is convex.
11. In a semiconductor device: a substrate having a die attach area, a semiconductor die in the die attach area, a relatively stiff die attach material bonding a central portion of the die to the substrate, and a more flexible die attach material bonding an edge portion of the die to the substrate.
12. The device of Claim 11 wherein the relatively stiff die attach material has a higher thermal conductivity than the more flexible material.
13. In a method of attaching a semiconductor die to a substrate, the steps of: forming a non-planar surface on one of said die and said substrate such that when the die and the substrate are positioned in facing relationship a central portion of the die is closer to the substrate than an edge portion, bonding the die to the substrate in the facing relationship with a first die attach material between the central portion of the die and the substrate and a second die attach material between the edge portion of the die and the substrate.
1 . The method of Claim 13 wherein the substrate is formed with a non-planar surface on which the die is mounted.
15. In a method of attaching a semiconductor die to a substrate, the steps of: forming a non-planar surface on one of said die and said substrate such that when the die and the substrate are positioned in facing relationship a central portion of the die is closer to the substrate than an edge portion, bonding the die to the substrate in the facing relationship with a die attach material which fills the region between the die and the substrate and forms a joint which is relatively thin toward the central portion of the die and thicker toward the edge portion.
16. The method of Claim 15 wherein the non-planar surface is formed on the substrate by forming a die attach area having a raised central portion and a recessed outer portion.
17. The method of Claim 16 wherein the central and outer portions of the die attach area are both formed with generally planar surfaces.
18. The method of Claim 16 wherein the outer portion of the die attach area is formed with a concave surface.
19. The method of Claim 16 wherein the central portion of the die attach area is formed with a surface which is planar toward its middle and rounded toward its periphery.
20. The method of Claim 16 wherein the central portion of the die attach area is formed with a convex surface.
21. In a method of attaching a semiconductor die to a substrate: bonding the die to the substrate with a first die attach material between a central portion of the die and the substrate and a second die attach material between an edge portion of the die and the substrate.
EP19900916935 1989-10-05 1990-10-05 Die attach structure Withdrawn EP0495005A1 (en)

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US41773089A 1989-10-05 1989-10-05
US417730 1989-10-05

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JPH06502962A (en) 1994-03-31

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