Characteristics of Sn–Cu Solder Bump Formed by Electroplating for Flip Chip
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Bibliographic record
Abstract
Sn–Cu near eutectic solder bump was fabricated by electroplating for flip-chip, and its electroplating and bump characteristics were studied. A Si-wafer was used as a substrate and the under bump metallization (UBM) comprised 400 nm of Al, 300 nm of Cu, 400 nm of Ni, and 20 nm of Au sequentially from bottom to the top of the metallization. The electrolyte for plating Sn–Cu solder consisted of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$hbox Sn^+2$</tex> (concentration of 30 g/L) and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$hbox Cu^+2$</tex> (0.3 g/L) solutions with methasulfonic acid and deionized water. The experimental results showed that the plating ratio of the Sn–Cu increased from 0.25 to 2.7 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$mu/hbox min$</tex> with increasing current density from 1 to 8 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$hbox A/dm^2$</tex> . In this range of current density, the plated Sn–Cu maintained its composition nearly constant level as Sn-(0.9 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$sim$</tex> 1.4)wt% Cu. The solder bump of typical mushroom shape with 120- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhbox m$</tex> stem diameter and 75- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhbox m$</tex> height was formed by plating at 5 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$hbox A/dm^2$</tex> for 2 h. The mushroom bump changed its shape to the hemispherical type of 140- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$muhbox m$</tex> diameter by air reflow on a hot plate at 260 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circhbox C$</tex> . The homogeneity of element distribution in the solder bump was examined, and Sn content in the mushroom bump appears to be uneven changed to more uniform after the air reflow. The highest shear bond strength of the Sn–Cu hemispherical bump showed 113 gf by reflowing at 260 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circhbox C$</tex> for 10 s.
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Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
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