Technical challenges of stencil printing technology for ultra fine pitch flip chip bumping

Manessis, D.; Patzelt, R.; Ostmann, A.; Aschenbrenner, R.; Reichl, H.

doi:10.1016/s0026-2714(03)00361-5

Cited by 59 publications

(25 citation statements)

References 3 publications

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“…Stencil printing has a much lower cost, but it is highly doubtful for fine-pitch bumping. 19 Most Pbfree solders in flip chips are currently Sn-based alloys, such as Sn-3.5wt.%Ag, Sn-0.7wt.%Cu, and Sn-3.8wt.%Ag-0.7wt.%Cu. 7,20 In addition to solder bumping, the under bump metallurgy (UBM) is another key issue.…”

Section: Introductionmentioning

confidence: 99%

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Kim

et al. 2004

Journal of Elec Materi

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Pure Ni, the Ni-Cu alloy, and pure Cu layers as the under bump metallurgy (UBM) for a flip-chip solder joint were deposited by electrolytic plating. For the pure Ni layer, residual stress can be controlled by adding a wetting agent and decreasing current density, and it is always under tensile stress. The Ni-Cu alloys of different Cu compositions from ϳ20wt.%Cu to 100wt.%Cu were deposited with varying current density in a single bath. The residual stress was a strong function of current density and Cu composition. Decreasing current density and increasing Cu content simultaneously causes the residual stress of the metal layers to sharply decrease. For the pure Cu layer, the stress is compressive. The Cu layer acts as a cushion layer for the UBM. The residual stress of the UBM strongly depends on the fraction of the Cu cushion layer. Interfacial reaction of the UBM with Sn-3.5 wt.% Ag was studied. As the Cu contents of Ni-Cu alloys increased, the dissolution rate increased. Several different intermetallic compounds (IMCs) were found. The lattice constants of alloys and the IMC increase with increasing Cu contents because the larger Cu atoms substitute for the smaller Ni atoms in the crystallites. The Cu content of the IMC are strongly dependent on the composition of the alloys. Ball shear tests were done with different metal-layer schemes. The failure occurs through the IMC and solder.

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Section: Introductionmentioning

confidence: 99%

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Kim

et al. 2004

Journal of Elec Materi

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“…For last several decades, FC (flip chip), also known as C4 technology has been developed as a method for interconnecting functional devices on board, to externals with solder bumps that have been deposited onto the chip pads. [1] Different approaches for bump formation and interconnects have been developed so far, such as electroplating, [2,3] stencil printing, [4,5] solder droplet printing. [6] Although the continuous efforts have been made to move to the finer and larger number of micro interconnects, there are several fatal concerns on the high process complexity and the drastic cost increase of conventional process and the lack of the design flexibility.…”

Section: Introductionmentioning

confidence: 99%

Process design of self-replication for micro bump formation

Yasuda

2010

2010 IEEE CPMT Symposium Japan

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For the bumping of BGA, CSP, and FC packaging, the trade-off of the cost-effectiveness (materials and instrument cost, productivity) and the performance (pitch, fan-out, precision, reliability) arises. To meet both demands, some unique concepts and the flexible methodology by using solder micro-fillers/polymer materials have been proposed. The self-replication phenomena of the twin micro bumps, typically several hundreds micrometers, from a single micro bridge in the resin media was focused. A couple of micro molten droplets-on-lands out of a vertically bridged bump could form in a small parallel gap filled with the resin between two co-planar substrates which are moved apart with the balance of surface tension among molten solder, polymer liquids, and metal traces. In order to optimize the process, the effects of the physical properties of the solder alloys and filler size were examined through the X-ray observations of the formed micro bumps before detachements.

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“…As the stencil printing method has the benefit of reducing the price of the big pitched-devices, it has been the subject of many researches. 4) Other advantages of employing a stencil printing method for wafer level packaging are its compatibility with the conventional reflow machine and new solder materials, the composition of which can vary in a wide range.…”

Section: Introductionmentioning

confidence: 99%

Flip Chip Bump Formation of Sn–1.8Bi–0.8Cu–0.6In Solder by Stencil Printing

Lee¹,

Jung

Cheon³

et al. 2005

Mater. Trans.

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Flip chip bumping by stencil printing method using a new composition of solder paste, Sn-1.8%Bi-0.8%Cu-0.6%In, all in mass%, was investigated. Sn-3.5%Ag, Sn-37%Pb and Sn-36%Pb-2%Ag were selected as references for the experiment. The solder pastes were printed on the under bump metallization (UBM) of a Si-wafer using a stencil, where diameter and thickness of the stencil opening were 400 and 150 mm, respectively. The UBM deposit comprised 0.4 mm each of Al, Ni and Cu, and 20 nm of Au from bottom to top of the metallization, sequentially. The printed paste bumps were reflow soldered in air, and the peak soldering temperature of Sn-1.7Bi-0.8Cu-0.6In and Sn-3.5Ag was 523 K and of Sn-37Pb and Sn-36Pb-2Ag was 503 K. From the experimental results the solder bumps of Sn-1.8Bi-0.8Cu-0.6In alloys were well-formed with a mean height of 260 mm. The shear strength of Sn-1.8Bi-0.8Cu-0.6In at 523 K (as-reflowed) showed the highest value of 6.5N followed by those of Sn-3.5Ag, Sn-37Pb and Sn-36Pb-2Ag solders. After 1000 h aging, while the shear strength of the Sn-1.8Bi-0.8Cu-0.6In showed 27% decrease compared to as-reflowed conditions, it was still 15-30% higher than those of Sn-37Pb, Sn-36Pb-2Ag and Sn-3.5Ag solders. Intermetallic compounds (IMCs) formed on the interface between solder and UBM were (Cu,Ni) 6 Sn 5 . As aging time went on up to 1000 h, the content of Ni in the IMC changed from 6.6% at initial stage (as-reflowed) to 13.5% at final stage (1000 h aging).

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Technical challenges of stencil printing technology for ultra fine pitch flip chip bumping

Cited by 59 publications

References 3 publications

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Process design of self-replication for micro bump formation

Flip Chip Bump Formation of Sn–1.8Bi–0.8Cu–0.6In Solder by Stencil Printing

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Technical challenges of stencil printing technology for ultra fine pitch flip chip bumping

Cited by 59 publications

References 3 publications

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Process design of self-replication for micro bump formation

Flip Chip Bump Formation of Sn&ndash;1.8Bi&ndash;0.8Cu&ndash;0.6In Solder by Stencil Printing

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Flip Chip Bump Formation of Sn–1.8Bi–0.8Cu–0.6In Solder by Stencil Printing