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Research Papers

Gold-Tin Solder Wetting Behavior for Package Lid Seals

[+] Author and Article Information
Paul T. Vianco

Sandia National Laboratories,
P.O. Box 5800 MS0889,
Albuquerque, NM 87185-0889
e-mail: ptvianc@sandia.gov

Alice C. Kilgo, Bonnie M. McKenzie

Sandia National Laboratories,
P.O. Box 5800 MS0889,
Albuquerque, NM 87185-0889

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received October 24, 2017; final manuscript received March 20, 2018; published online May 9, 2018. Assoc. Editor: Eric Wong.

J. Electron. Packag 140(2), 021003 (May 09, 2018) (18 pages) Paper No: EP-17-1115; doi: 10.1115/1.4039749 History: Received October 24, 2017; Revised March 20, 2018

This study examined the cause of nonwetted regions of the gold (Au) finish on iron-nickel (Fe–Ni) alloy lids that seal ceramic packages using the 80Au-20Sn solder (wt %, abbreviated Au–Sn) and their impact on the final lid-to-ceramic frame solder joint. The Auger electron spectroscopy (AES) surface and depth profile techniques identified surface and through-thickness contaminants in the Au metallization layer. In one case, the AES analysis identified background levels of carbon (C) contamination on the surface; however, the depth profile detected Fe and Ni contaminants that originated from the plating process. The Fe and Ni could impede the completion of wetting and spreading to the edge of the Au metallization. The Au layer of lids not exposed to a Au–Sn solder reflow step had significant surface and through-thickness C contamination. Inorganic contaminants were absent. Subsequent simulated reflow processes removed the C contamination from the Au layer without driving Ni diffusion from the underlying solderable layer. An Au metallization having negligible C contamination developed elevated C levels after exposure to a simulated reflow process due to C contamination diffusing into it from the underlying Ni layer. However, the second reflow step removed that contamination from the Au layer, thereby allowing the metallization to support the formation of lid-to-ceramic frame Au–Sn joints without risk to their mechanical strength or hermeticity.

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References

Olsen, D. , and Berg, H. , 1979, “Properties of Die Bond Alloys Relating to Thermal Fatigue,” IEEE Trans. Compon., Hybrids, Manuf. Technol., 2(2), pp. 257–263. [CrossRef]
Vianco, P. , 1999, “An Overview of Surface Finishes and Their Role in Printed Circuit Board Solderability and Solder Joint Performance,” Circuit World, 25(1), pp. 6–24. [CrossRef]
Holmes, P. , and Loasby, R. , 1976, Handbook of Thick Film Technology, Electrochemical Publications, Ayr, UK.
Matijasevic, G. , Lee, C. , and Wang, C. , 1993, “Au-Sn Alloy Phase Diagram and Properties Related to Its Use as a Bonding Medium,” Thin Solid Films, 223(2), pp. 276–287. [CrossRef]
Oppermann, H. , 2005, “The Role of Au/Sn Solder in Packaging,” Materials for Information Technology, E. Zshech , C. Whelan , and T. Mikolajick , eds., Springer, London, pp. 377–390. [CrossRef]
Ivey, D. , 1998, “Microstructural Characterization of Au/Sn Solder for Packaging in Optoelectronics Applications,” Micron, 29(4), pp. 281–287. [CrossRef]
Christie, I. , and Cameron, B. , 1994, “Gold Electrodeposition Within the Electronics Industry,” Gold Bull, 27(1), pp. 12–20. [CrossRef]
Etchmaier, H. , Novak, J. , Hannes, E. , and Hadley, P. , 2012, “Reaction Dynamics of Diffusion Soldering With the Eutectic Au-Sn Alloy on Copper and Silver Substrates,” Intermet., 20(1), pp. 87–92. [CrossRef]
Zhu, Z. , Li, C. , Liao, L. , Liu, C. , and Kao, C. , 2016, “Au-Sn Bonding Material for the Assembly of Power Integrated Circuit Module,” J. Alloys Compd., 671, pp. 340–345. [CrossRef]
Vuorinen, V. , Rautiainen, A. , Heikkinen, H. , and Krockel-Paulasto, M. , “Optimization of Contact Metallizations for Reliable Wafer Level Au-Sn Bonds,” Microelectron. Reliab., 64, pp. 676–680. [CrossRef]

Figures

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Fig. 7

(a) Photograph shows lid 1 with the Au–Sn solder reflowed on the Ni/Au metallization. The yellow box indicates an area of incomplete coverage by the Au–Sn solder. (b) High magnification photograph shows the nonwetted Au layer.

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Fig. 6

Schematic diagrams show the steps to fabricate the Au–Sn lid (seal) solder joint. (a) These process steps reflow the Au–Sn solder on the lid structure (top). The Au–Sn solder is tack welded on the Ni/Au metallization (middle). The reflow step allows wetting and spreading of the molten Au–Sn solder (bottom). (b) Process steps show formation of the Au–Sn solder joint between the lid and ceramic frame. The lid-plus-Au–Sn solder is placed over the ceramic frame (top). Pressure is applied to the lid during the reflow step to support wetting and spreading activity by the molten Au–Sn solder to complete the joint (bottom).

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Fig. 5

SEM image shows the interface between the ceramic frame's metallization and the Au–Sn solder at the location indicated by the yellow rectangle in the inset photograph. The Au had not yet fully dissolved into the volume of molten Au–Sn solder.

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Fig. 4

(a) SEM image shows the lid (Ni layer)/Au–Sn solder interface. ((b) and (c)) EDX maps show the area distributions of Ni together with Sn, as well as that of Au.

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Fig. 3

(a) SEM photograph shows the fillet of an Au–Sn solder joint made to the Ni-plated, Kovar™ lid and ceramic substrate and (b) higher magnification image was taken of the lid (Ni layer)/Au–Sn solder interface. A reaction layer, which formed along the interface, was accompanied by intermittent voids.

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Fig. 2

SEM photograph shows the metallization layer—Mo thick film adhesion layer, Ni/Ni-Co solderable layer, and the Au protective layer placed on the ceramic frame (substrate)

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Fig. 1

(a) Photograph shows a microprocessor ceramic package in its lead frame; (b) top-down view outlines the ceramic frame, lid, and the leads; and (c) the cross section A-A' shows a profile view of the lid attached to the ceramic frame. The white ovals identify the location of the lid-to-ceramic solder bond.

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Fig. 9

The time-temperature profile that simulates the supplier Au–Sn reflow process in nitrogen. The melting temperature is 278 °C for the Au–Sn solder.

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Fig. 10

The upper photograph shows the Gleeble™ 3500 equipment used to expose lids 3 and 4 to the Au–Sn reflow profile under nitrogen and air atmospheres, respectively. The lower photograph shows the lid 3 on the heating platen and associated thermal couples to monitor its temperature.

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Fig. 12

((a) and (b)) The SEM images show the two locations “A” and “B” where the AES analysis was performed on lid 1, which had the supplier-reflowed, Au–Sn solder. Four features were examined per location: site 1, Ni layer that covered the entire lid surface; site 2, the surface of Au metallization that was not wetted by the Au–Sn solder; site 3, a precursor film at the edge of the Au–Sn solder; and site 4, on top of the Au–Sn solder “bulk.”

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Fig. 11

SEM photograph provides a cross section view of the lid that highlights the Ni and Au layers from which were measured their respective thicknesses

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Fig. 8

Photograph shows lid 3 that had the Au–Sn preform removed to reveal the Ni/Au metallization. The AES analysis was performed at the four locations, A, B, C, and D.

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Fig. 15

SEM images show the cross section made through lid 1 (lot A), which had the Au–Sn solder reflowed at the supplier: (a) SEM photograph shows the entire solder coating and locations of the higher magnification images; (b) SEM image shows the Au–Sn solder and its interface with the lid at the center location; and (c) SEM photograph was taken at the edge of the Au–Sn solder, showing the contact angle, θc, and the segment (X-Y) of Au layer that was not covered by the solder

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Fig. 13

(a) Low magnification image shows the location of the AES surface survey (solid rectangle) and depth profile (dashed rectangle) performed at a nonwetted area of the Ni/Au metallization on lid 1 and (b) high magnification SEM photograph shows the smooth surface topography at the site of the depth profile

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Fig. 16

Photograph shows lid 3 after having the Au–Sn preform removed from the Au metallization. The AES analysis was performed at the four sites A, B, C, and D.

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Fig. 14

((a) and (b)) Graphs show the elemental traces from the AES depth profile performed on the nonwetted, Au layer shown in Fig. 13(b) (Lid 1) using two different axes scales

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Fig. 17

AES depth profile shows the C and Au signals in the Au metallization of lid 3 (lot B) that was not exposed to the Au–Sn solder reflow process. Data are shown for locations A and B, which are also representative of locations C and D.

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Fig. 18

AES depth profile shows the C and Au signals obtained from locations A and D on the Au layer of lid 3 after exposure to the simulated, nitrogen reflow process

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Fig. 24

AES depth profile that was taken of the Ni layer at the center of lid 5 after exposure to the belt furnace reflow process (nitrogen)

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Fig. 25

(a) Photograph shows lid 6 after exposure to the belt furnace reflow process. Two locations, A and B, are shown at higher magnification in (b) and (c), respectively. The AES analyses were performed on the nonwetted Au layer, the precursor film (Au–Sn solder), and the Au–Sn solder.

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Fig. 19

AES depth profile shows the Si and O signals on the Au metallization of lid 3 following exposure to the simulated reflow process (nitrogen)

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Fig. 20

AES depth profile shows the C and Au signals obtained from locations A and D on the Au layer of lid 4 after exposure to the simulated, air reflow process

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Fig. 21

AES depth profile shows the baseline C and Au signals obtained from locations C and D on the Au layer of lid 5

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Fig. 26

AES depth profile taken at the nonwetted region of location A on lid 6 that was exposed to the belt furnace reflow process

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Fig. 22

AES depth profile shows the first 2.5 min of a 10 min depth profile taken at one of two locations on the nonreflowed, Au–Sn preform removed from lid 5

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Fig. 23

AES depth profile that was taken after lid 5 was exposed to the belt furnace reflow process (nitrogen). The Au–Sn preform was not replaced on the lid. The sites were just to the side of the those used to obtain the baseline data in Fig.21.

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Fig. 27

AES depth profile taken at the precursor film region of location A on lid 6 after exposure to the belt furnace reflow process

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Fig. 28

AES depth profile taken at the bulk Au–Sn solder of location B on lid 6 after exposure to the belt furnace reflow process

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Fig. 29

(a) X-ray radiograph shows a section of the Au–Sn solder joint made between lid 7 and the ceramic frame. The fillet (outside) and the joint gap are identified in the image. The white bracket indicates the location where the Au–Sn solder did not wet-and-spread completely over the Au layer belonging to the lid. (b) A higher magnification image shows the Au–Sn solder joint at the location of the yellow box in image (a). The radiograph illustrates the extent of nonwetting versus the full footprint of the joint identified by the label, “Au–Sn solder joint gap.”

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Fig. 30

Photograph shows the locations of the four cross sections made to the Au–Sn solder joint between lid 7 and the ceramic frame

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Fig. 31

Series of SEM photographs show the complete wetting and spreading by the Au–Sn solder over the Au metallization at section #2 of lid 7. The magenta arrow indicates the excellent fillet formation. The high magnification images confirm spontaneous wetting and spreading of Au–Sn solder to the edge of the lid's metallization outside of the joint gap.

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Fig. 32

Series of SEM photographs that exemplify failure of the Au–Sn solder to completely cover the Au metallization at section #2 on the other side of the lid 7. The high magnification images confirm the generally good solderability of the Au metallization on the lid as shown by the relatively low contact angle, θc. Solderability was also excellent on the metallization of the ceramic frame.

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Fig. 33

Series of SEM photographs that show failure of the Au–Sn solder to completely cover the Au metallization at section #3 (lid 7). The geometry of the internal fillet shows a small contact angle, θc, that signifies generally good solderability of the Au metallization.

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