Enhanced Ball Shear Testing Configuration For Substrate LGA Sensor Devices

Semiconductor assembly mass production environment has means of testing and verifying bond consistency and reliability during wire bonding. Common bond integrity assessment is ball shear testing (BST). This test enables analysis of the strength between the bond pad and a ball bond. This paper presents significant procedure on how ball shear testing parameters should be treated during wirebond integrity check. Device complexity in terms of performing ball shear testing specifically on sensor dice has different output responses. Frequent shearing on die resulted as bond pads are elevated by 30 µm (microns). To address manufacturing in-process controls challenges, shearing tool position, dage settings, and optical scopes are taken into consideration. Also, a study was performed on the execution correctness in combination with proper dage parameters was explored to meet good ball shear test process capability and break modes.

Nucleation and Morphology of Cu6Sn5 Intermetallic at the Interface between Molten Sn-0.7Cu-0.2Cr Solder and Cu Substrate

The nucleation kinetics and morphology of Cu6Sn5 IMCs at the interface between a Sn-0.7Cu-0.2Cr solder and Cu substrate were investigated in this study. A Sn-0.7Cu solder was utilized as a reference to elucidate the impact of Cr addition. The mechanical properties of the solder joints were determined via ball-shear tests. Cu coupons were dipped in the molten solders for 1 and 3 s at 240–300 °C, and the morphological analyses were conducted via electron microscopy. Both the solders contained scallop-like Cu6Sn5 IMCs. The smallest Cu6Sn5 IMCs were observed at 260 °C in both the solders, and the particle size increased at 280 and 300 °C. The IMCs in the Sn-0.7Cu-0.2Cr solder were smaller and thinner than those in the Sn-0.7Cu solder at all the reaction temperatures. The thickness of the IMCs increased as the reaction temperature increased. Inverse C-type nucleation curves were obtained, and the maximum nucleation rate was observed at an intermediate temperature. The shear strengths of the Sn-0.7Cu-0.2Cr solder joints were higher than those of the Sn-0.7Cu solder joints. This study will facilitate the application of lead-free solders, such as Sn-0.7Cu-0.2Cr, in automotive electrical components.

Wirebond Process Improvement through Silicon Die Polyimide Removal

This study aims to develop polyimide etching process on the silicon die after decapsulation to resolve the wire shear issue during ball shear data gatherings. The shear strength of the ball is affected by the presence of polyimide insulator during ball shearing process, due to the polyimide layer of the silicon die being coplanar with the ball height of the wire. Experimentation and statistical analysis were done on units with and without polyimide coating, with Sodium Hydroxide (NaOH) used to remove the excess polyimide. Results revealed that silicon dice without polyimide coating resulted to better reading in terms of ball shear.

A Critical Review of Wirebond Visual Inspection Criteria

Wirebond engineers and technicians primarily rely on three means by which to evaluate the integrity and reliability of a wirebond interconnect. Destruct/non-destruct pull test, ball shear, cross-sections, intermetallic coverage under the ball are tests used to evaluate the mechanical strength as part of process development and in line process controls. Reliability testing and evaluation involves these same tests after prolonged environmental exposure such as, temp cycling, burn-in, humidity testing etc. according to standards such as AEC-Q100. Much has been written about the above. A third and very important consideration in wirebonding is visual inspection of the deformed wire after wirebond formation. The amount of wire squash-out, placement of the bond on the pad relative to nearby circuitry, looping profiles and heel integrity are all very important aspects of wirebond interconnect inspection. Poor workmanship can lead to noncompliant bonds per visual inspection criteria and can directly impact the reliability of the finished product. Bond pad inspection prior to bonding is also a critical aspect that is often overlooked. Historically, MIL-STD-883 has served as a baseline set of visual specs related to wirebond, and package assembly in general. Many company quality documents reference MIL-STD-883 TM 2017 and TM 2010 and/or cut and paste the bond inspection criteria into internal documents. This paper critically reviews the wirebond visual inspection criteria contained in MIL-STD-883 relative to the requirements of a fully optimized modern day wirebond process.

Solder Ball Robustness Comparison between SAC 387 and Polymer Solder Balls under AC and TC Reliability Test

Environment and the health concerns due to the hazardous effects of lead resulted in significant activities to find a replacement for lead-contained solders for electronics industrial. Majority of the semiconductor industrial are now replacing lead solders with Tin-Silver-Copper (SAC 387) solder balls. However, dropped balls in SAC 387 for Ball Grid Array (BGA) products due to poor solder joint strength caused by high thermal stress are a major concern in the semiconductor industries. Polymer core inside the solder ball (polymer core/Cu/Sn) is thus integrated to improve the solder ball joint strength. The function of polymer core inside the solder ball is to absorb and released the stress better as compared to the SAC 387 solder ball. Since the diffusion rate of Cu is faster than the diffusion rate of Sn, hence, this could caused the Kirkendall voids tends to form in between the Cu and Sn IMC layer. This would affect the solder ball joint strength and causing drop balls issue. By implement with an extra of Ni layer to the polymer core solder ball (core/Cu/Ni/Sn), could reduce the diffusion from Cu to Sn, thus to overcome the Kirkendall voids and to further improve the solder ball joint strength. This research work studies the performance of the solder ball shear strength of the two types of solder balls applied to MAPBGA device. In this research, both SAC 387 and polymer solder balls were went through under AC (Autoclave) and TC (Temperature Cycle) reliability test up to 144 hours and 1000 cycles, respectively. Solder ball shear strength test was conducted via Dage 4000 series bond tester. From the research work results of the two types of solder balls, the ball shear strength were decreased with an increased of aging and cycles. Overall, it can be concluded that the polymer core solder ball with an additional of Ni layer showed better performance than the polymer core without Ni layer and SAC 387 solder balls, after subjected to the AC and TC reliability test.