• Journal of Welding and Joining
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• v.20 no.6
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• pp.783-788
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• 2002

Sn-Ag-Cu solder is known as most competitive in many kinds of Pb-free solders. In this study, effects of solderability with plated layers such as Cu, Cu/Sn, Cu/Ni and Cu/Ni/Au were investigated. Sn-3.5Ag-0.7Cu solder balls were reflowed in commercial reflow machine (peak temp.:$250^{\circ}C$and conveyer speed:0.6m/min). In wetting test, immersion speed was 5mm/sec., immersion time 5sec., immersion depth 4mm and temperature of solder bath was $250^{\circ}C$. Wettability of Sn-3.5Ag-0.7Cu on Cu, Cu/Sn ($5\mu\textrm{m}$), Cu/Ni ($5\mu\textrm{m}$), and Cu/Ni/Au ($5\mu\textrm{m}/500{\AA}$) layers was investigated. Cu/Ni/Au layer had the best wettability as zero cross time and equilibrium force, and the measured values were 0.93 sec and 7mN, respectively. Surface tension of Sn-3.5Ag-0.7Cu solder turmed out to be 0.52N/m. The thickness of IMC is reduced in the order of Cu, Cu/Sn, Cu/Mi and Cu/Ni/Au coated layer. Shear strength of Cu/Ni, Cu/Sn and Cu was around 560gf but Cu/Ni/Au was 370gf.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.4
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• pp.23-29
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• 2000

We demonstrate the fabrication method of high-density and high-quality solder bump solving a copper (Cu) cross-contamination in Si-LSI laboratory. The Cu cross-contamination is solved by separating solder-bump process by two steps. Former is via-formation process excluding Cu/Ti under ball metallurgy (UBM) layer sputtering in Si-LSI laboratory. Latter is electroplating process including Ti-adhesion and Cu-seed layers sputtering out of Si-LSI laboratory. Thick photoresist (PR) is achieved by a multiple coating method. After TiW/Al-electrode sputtering for electroplating and via formation in Si-LSI laboratory, Cu/Ti UBM layer is sputtered on sample. The Cu-seed layer on the PR is etched during Cu-electroplating with low-electroplating rate due to a difference in resistance of UBM layer between via bottom and PR. Therefore Cu-buffer layer can be electroplated selectively at the via bottom. After etching the Ti-adhesion layer on the PR, Sn/Pb solder layer with a composition of 60/40 is electroplated using a tin-lead electroplating bath with a metal stoichiometry of 60/40 (weight percent ratio). Scanning electron microscope image shows that the fabricated solder bump is high-uniformity and high-quality as well as symmetric mushroom shape. The solder bumps with even 40/60 $\mu\textrm{m}$ in diameter/pitch do not touch during electroplating and reflow procedures. The solder-bump process of high-uniformity and high-density with the Cu cross-contamination free in Si-LSI laboratory will be effective for electronic microwave application.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.505-509
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• 2002

Pb is considered to be eliminated from solder, due to its toxicity. However, melting temperatures of most Pb-free solders are known higher than that of Sn37Pb. Therefore, there is a difficulty to apply Pb-free solders to electronic industry. Since Sn3Ag8Bi5In has relatively lower melting range as $188~200^{\circ}C$, on this study. Wettability and soldering characteristics of Sn3Ag8Bi5In solder in BGA were investigated to solve for what kind of problem. Zero cross time, wetting time, and equilibrium force of Sn3Ag8Bi5In solder for Cu and plated Cu such as Sn, Ni, and Au/Ni-plated on Cu were estimated. Plated Sn on Cu showed best wettability for zero cross time, wetting time and equilibrium farce. Shear strength of the reflowed joint with Sn3Ag8Bi5In ball in BGA was investigated. Diameter of the ball was 0.5mm, UBM(under bump metallurgy) was $Au(0.5\mu\textrm{m})Ni(5\mu\textrm{m})/Cu(18\mu\textrm{m})$ and flux was RMA type. For the reflow soldering, the peak reflow temperature was changed in the range of $220~250^{\circ}C$, and conveyor speed was 0.6m/min.. The shear strength of Sn3Ag8Bi5In ball showed similar level as those of Sn37Pb. The soldered balls are aged at $110^{\circ}C$ for 36days and their shear strengths were evaluated. The shear strength of Sn3Ag8Bi5In ball was increased from 480gf to 580gf by aging for 5 days.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.219-221
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• 2005

Sn-9Zn solder balls were bonded to Cu, ENIG (Electroless Nickel/Immersion Gold) and electrolytic Au/Ni pads, and the effect of aging on their joint reliability was investigated. The interfacial products were different from the general reaction layer formed in a Sn-base solder. The intermetallic compounds formed in the solder/Cu joint were $Cu_{5}Zn_{8}$ and $Cu_{6}Sn_{5}$. After aging treatment, voids formed irregularly at the bottom side of the solder because of Sn diffusion into the $Cu_{5}Zn_{8}$ IMC. In the case of the solder/ENIG joint, $AuZn_{3}$ IMCs were formed at the interface. In the case of the Au/Ni/Cu substrate, an $AuZn_{3}$ IMC layer formed at the interface due to the fast reaction between Au and Zn. In addition, the $AuZn_{3}$ IMC layer became detached from the interface after reflow. When the aging time was extended to 100 h, $Ni_{5}Zn_{21}$ IMC was observed on the Ni substrate.

• Korean Journal of Materials Research
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• v.9 no.3
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• pp.288-294
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• 1999

In the flip chip interconnection using solder bump, the Under Bump Metallurgy (UBM) is required to perform multiple functions in its conversion of an aluminum bond pad to a solderable surface. In this study, various UBM systems such as $Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 5\mu\textrm{m}, Al 1\mu\textrm{m} / Ti 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}, al 1\mu\textrm{m}/Ni 0.2\mu\textrm{m} / Cu 1\mu\textrm{m} and Al 1\mu\textrm{m}/Pd 0.2\mu\textrm{m} / Cu 1\mu\textrm{m}$ for flip chip interconnection using the low melting point eutectic 63Sn-37Pb solder were investigated and compared to their metallurgical properties. $100\mu\textrm{m}$ size bumps were prepared for using an electroplating process. The effects of the number of reflows and aging time on the growth of intermetallic compounds(IMC) were investigated. $Cu_6Sn_5$ and $Cu_3Sn$ IMC were abserved after aging treatment in the UBM system with thick coper $(Al 1\mu\textrm{m}/Ti 0.2\mu\textrm{m}/Cu 5\mu\textrm{m})$. However only the $Cu_6Sn_5$ was detected in the UBM system with $1\mu\textrm{m}$ thick copper even after 2 reflow and 7 day aging at $150^{\circ}C$. Complete Cu consumption by Cu-Sn IMC growth gives rise to a direct contact between solder inner layer such as Ti, Ni and Pd, and hence to possibly cause reactions between two of them. In this study, however, only for the Pd case, IMC of PdSn. was observed by Cu consumption. UBM interfacial reactions with s이der affected the adhesion strength ot s이der balls after s이der reflow and annealing treatment.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.114-117
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• 2003

본 연구에서는 계산을 통해 나온 Sn-Ag-Cu 삼원계 공정점(Sn-3.7Ag-0.9Cu)을 바탕으로 그 근처의 응고경로가 다른 6가지 조성(Sn-4.6Ag-0.4Cu, Sn-4.9Ag-1.0Cu, Sn-3.9Ag-1.3Cu, Sn-2.2Ag-1.2Cu, Sn-2Ag-0.7Cu, Sn-2.7Ag-0.3Cu)에 대한 솔더합금의 미세조직을 관찰하였다. 응고경로는 $L\;\rightarrow\;L+Primary\;\rightarrow\;L+Primary+Secondary\;\rightarrow\;Ternary\;Eutectic+Primary+Secondary$로 되며 6가지 경우를 예상할 수 있다 솔더합금의 미세조직은 느린 냉각으로 인하여 빠른 냉각, 보통 냉각에 비해 상대적으로 커다란 $\beta-Sn$ dendrite를 보였고 $Ag_3Sn,\;Cu_6Sn_5$과는 다르게 $\beta-Sn$는 약 $30^{\circ}C$의 과냉(DSC분석)이 존재하게 되어 Sn-4.6Ag-0.4Cu의 경우에는 $Ag_3Sn$상이, Sn-2.2Ag-1.2Cu의 경우에는 $Cu_6Sn_5$가 과대성장을 하였다. 솔더의 기계적 특성을 살펴보고자 Cu 기판위에서 각 조성의 솔더볼을 솔더링한 후 다양한 냉각 속도를 적용하여 reflow 솔더링을 하고 솔더/기판 접합에 대한 전단 강도 시험을 실시했다. 냉각 속도가 빠를수록 $\beta-Sn$의 dendrite가 미세해져서 높은 전단 강도를 보였고 6가지 조성의 솔더볼중 공정조직 분율이 낮은 Sn-2Ag-0.7Cu 조성의 경우에서 낮은 전단 강도가 나타났다.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.65-70
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• 2021

In this study, interfacial properties and mechanical properties of joints were reported after Cu pads finished with organic solderability preservative (OSP) on flame retardant-4 (FR-4) printed circuit board (PCB) and electronic components were joined with a Sn-57Bi-1Ag solder paste by using a laser bonding process. The laser bonding process was performed under various bonding conditions with changing a laser power and a bonding time and effects of bonding conditions on interfacial and mechanical properties of joints were analyzed. In order to apply for industry, properties of bonding joints using a reflow bonding process which are widely used were compared. When the laser bonding process were performed, we observed that Cu₆Sn₅ intermetallic compounds (IMCs) were fully formed at the interface although the bonding times were very short about 2 and 3 s. Furthermore, void formations of the joints by using the laser bonding process were suppressed at the joints with comparing to the reflow bonding process and shear strengths of bonding joints were higher than that by using the reflow bonding process. Therefore, in spite of a very short bonding time, it is expected that joints will be stably formed and have a high mechanical strength by using the laser bonding process.

• Journal of the Microelectronics and Packaging Society
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• v.10 no.4
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• pp.39-46
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• 2003

Sn-Cu eutectic solder bump was fabricated by electroplating for flip chip and its characteristics were studied. A Si-wafer was used as a substrate and the UBM(Under Bump Metallization) of Al(400 nm)/Cu(300 nm)/Ni(400 nm)/Au(20 nm) was coated sequentially from the substrate to the top by an electron beam evaporator. The experimental results showed that the plating ratio of the Sn-Cu increased from 0.25 to 2.7 $\mu\textrm{m}$/min with the current density of 1 to 8 A/d$\m^2$. In this range of current density the plated Sn-Cu maintains its composition nearly constant level as Sn-0.9∼1.4 wt%/Cu. The solder bump of typical mushroom shape with its stem diameter of 120 $\mu\textrm{m}$ was formed through plating at 5 A/d$\m^2$ for 2 hrs. The mushroom bump changed its shape to the spherical type of 140 $\mu\textrm{m}$ diameter by air reflow at $260^{\circ}C$. The homogeneity of chemical composition for the solder bump was examined, and Sn content in the mushroom bump appears to be uneven. However, the Sn distributed more uniformly through an air reflow.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.1
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• pp.33-38
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• 2001

We investigate the via-size dependance of as-electroplated- and reflow-bump shapes for realizing both high-density and high-aspect ratio of solder bump. The solder bump is fabricated by subsequent processes as follows. After sputtering a TiW/Al electrode on a 5-inch Si-wafer, a thick photoresist for via formation it obtained by multiple-codling method and then vias with various diameters are defined by a conventional photolithography technique using a contact alinger with an I-line source. After via formation the under ball metallurgy (UBM) structure with Ti-adhesion and Cu-seed layers is sputtered on a sample. Cu-layer and Sn/pb-layer with a competition ratio of 6 to 4 are electroplated by a selective electroplating method. The reflow-bump diameters at bottom are unchanged, compared with as-electroplated diameters. As-electroplated- and reflow-bump shapes, however, depend significantly on the via size. The heights of as-electroplated and reflow bumps increase with the larger cia, while the aspect ratio of bump decreases. The nearest bumps may be touched by decreasing the bump pitch in order to obtain high-density bump. The touching between the nearest bumps occurs during the overplating procedure rather than the reflowing procedure because the mushroom diameter formed by overplating is larger than the reflow-bump diameter. The arrangement as zig-zag rows can be effective for realizing the flip-chip-interconnect bump with both high-density and high-aspect ratio.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2007.04a
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• pp.37-47
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• 2007

Factor : Structure Metal pad & SMO size Board level TC test : - Large SMO size better Board level Drop test : - Large SMO size better Factor : Structure Substrate thickness Board level TC test : - Thick substrate better Board level Drop test : - Substrate thickness is not a significant factor for drop test Factor : Material Solder alloy Board level TC test : - Not so big differences over Pb-free solder and NiAu, OSP finish Board level Drop test : - Ni/Au+SAC105, CuOSP+LF35 are better Factor : Material Pad finish Board level TC test : - NiAu/NiAu is best Board livel Drop test : - CuOSP is best Factor : Material Underfill Board level TC test - Several underfills (reworkable) are passed TCG x500 cycles Board level Drop test : - Underfill lots have better performance than non-underfill lots Factor : Process Multiple reflow Board level TC test : - Multiple reflow is not a significant actor for TC test Board level Drop test : N/A Factor : Process Peak temp Board level TC test : - Higher peak temperature is worse than STD Board level Drop test : N/A Factor : Process Stack method Board level TC test : - No big difference between pre-stack and SMT stack Board level Drop test : - Flux dipping is better than paste dipping but failure rate is more faster