Fabrication and Reliability Assessment of Cu Pillar Micro-bumps with Printed Polymer Cores

Cu pillar micro-bumps with polymer cores have been demonstrated to effectively reduce thermomechanical stress and improve joint reliability. Fabricating polymer cores by a printing approach was proposed to overcome the limitations in conventional fabrication process. Cylindrical polymer cores with diameter of 20 µm and height of 30 µm were successfully printed. Surface metallization was subsequently applied on the printed polymer cores and Cu pillar micro-bumps with printed polymer cores with diameter of 35 µm and height of 35 µm were eventually achieved. To study the reliability performance of the interconnect joints made of Cu pillar micro-bumps with printed polymer cores, flip-chip bonding technology was successfully introduced and the interconnect joints between a designed BT substrate and a silicon chip were formed. The interconnect joints made of conventional Cu pillars with identical dimensions were prepared for comparison. The reliability performance of the joints was investigated under temperature cycling condition and drop condition, respectively. Printed polymer cores increased the characteristic life by 32% in a temperature cycling test (0°C-100°C), while the drop test showed that printed polymer cores increased the characteristic life by 4 times due to the extra compliance provided by the printed polymer cores. It can be concluded that Cu pillar micro-bumps with printed polymer cores can effectively reduce stress and improve joint reliability.

FCCSP IMC growth under reliability stress follows automotive criteria

Purpose The Kirkendall void had been a well-known issue for long-term reliability of semiconductor interconnects; while even the KVs exist at the interfaces of Cu and Sn, it may still be able to pass the condition of unbias long-term reliability testing, especially for 2,000 cycles of temperature cycling test and 2,000 h of high temperature storage. A large number of KVs were observed after 200 cycles of temperature cycling test at the intermetallic Cu3Sn layer which locate between the intermetallic Cu6Sn5 and Cu layers. These kinds of voids will grow proportional with the aging time at the initial stage. This paper aims to compare various IMC thickness as a function of stress test, the Cu3Sn and Cu6Sn5 do affected seriously by heat, but Ni3Sn4 is not affected by heat or moisture. Design/methodology/approach The package is the design in the flip chip-chip scale package with bumping process and assembly. The package was put in reliability stress test that followed AEC-Q100 automotive criteria and recorded the IMC growing morphology. Findings The Cu6Sn5 intermetallic compound is the most sensitive to continuous heat which grows from 3 to 10 µm at high temperature storage 2,000 h testing, and the second is Cu3Sn IMC. Cu6Sn5 IMC will convert to Cu3Sn IMC at initial stage, and then Kirkendall void will be found at the interface of Cu and Cu3Sn IMC, which has quality concerning issue if the void’s density grows up. The first phase to form and grow into observable thickness for Ni and lead-free interface is Ni3Sn4 IMC, and the thickness has little relationship to the environmental stress, as no IMC thickness variation between TCT, uHAST and HTSL stress test. The more the Sn exists, the thicker Ni3Sn4 IMC will be derived from this experimental finding compare the Cu/Ni/SnAg cell and Ni/SnAg cell. Research limitations/implications The research found that FCCSP can pass automotive criteria that follow AEC-Q100, which give the confidence for upgrading the package type with higher efficiency and complexities of the pin design. Practical implications This result will impact to the future automotive package, how to choose the best package methodology and what is the way to do the package. The authors can understand the tolerance for the kind of flip chip package, and the bump structure is then applied for high-end technology. Originality/value The overall three kinds of bump structures, Cu/Ni/SnAg, Cu/SnAg and Ni/SnAg, were taken into consideration, and the IMC growing morphology had been recorded. Also, the IMC had changed during the environmental stress, and KV formation was reserved.

FCCSP IMC Growth under Reliability Stress Following Automotive Standards

The Kirkendall void (KV) has been a well-known issue for long term reliability of semiconductor interconnects. KVs exist at the interfaces of Cu and Sn and the growing intermetallic compound (IMC) Cu6Sn5 at the initial stage, and a part of the IMC is converted to Cu3Sn when the environmental stress added. In this article, all the assembled packages pass the condition of unbiased long-term reliability testing, especially for 2,000 cycles of temperature cycling test and 2,000 h of high-temperature storage. A large numbers of KVs was observed after 200 cycles of temperature cycling. Various assembly structures were monitored, and various IMC thicknesses were concluded to be functions of stress test. Cu3Sn, Ni3Sn4, and Cu6Sn5 are not significantly affected by heat, but Ni3Sn4 grows steadily.

FCCSP IMC Growth under Reliability Stress follow Automotive Criteria

The kirkendall void had been a well-known issue for long term reliability of semiconductor interconnects, while even the KVs existing at the interfaces of Cu & Sn, it may still be able to pass the condition of un-bias long term reliability testing, especially for 2,000 cycles of temperature cycling test and 2,000hrs of high temperature storage. A large numbers of KVs was observed after 200cycles of temperature cycling test at the intermetallic Cu3Sn layer which locate between the intermetallic Cu6Sn5 & Cu layers. These kinds of voids will growth proportional with the aging time at initial stage, but slowing down attribute to the barrier layer of Cu3Sn & Cu interfaces. This paper compare various IMC thickness as a function of stress test, the Cu3Sn & Cu6Sn5 do affected seriously by heat, but Ni3Sn4 is not affected by heat or moisture.