Electroless Ni-P/Pd/Au Plating for Semiconductor Package Substrate

There have been so many reports about the solder joint reliability (SJR) of electroless Ni/Pd/Au plating (ENEPIG) for two decade. In these reports, almost electroless Ni plating is Ni-P and all immersion Au plating is pure gold. But electroless Pd plating has two type, pure Pd and Pd-P. In this study, the both influences of phosphorus content and thickness of electroless Pd plating film of ENEPIG were investigated on the solder-ball joint reliability with using a high-speed solder-ball shear test. In particular, we examined the SJR in the case of ENEPIG finished substrates that had undergone multiple reflow cycles. After reflow, we observed intermetallic compounds (IMCs) of interface between solder and ENEPIG. We consider that the shape of the IMCs is important factor that influences the SJR after multiple reflow cycles. Our results show that SJR of ENEPIG tends to be poorer on the condition of the higher phosphorus content and the thicker electroless Pd. We conclude that pure Pd plating has the widest thickness range, and that the optimum thickness of the pure Pd plating film is 0.05~0.2 μm. On the other hand, the high phosphorus content and thick Pd-P films extremely lower SJR of ENEPIG. We found that the structure of IMCs changed from dendrite type to dome type with the increase of P content in electroless Pd plating. Consequently, we inferred that the high adhesion at the dendrite type IMC/solder interface resulted in excellent solder-ball joint reliability after the reflow cycles.

On the solder ball joint reliability, the influence of electroless Pd deposition reaction process and Pd film thickness in electroless Ni/Pd/Au plating was examined. The solder ball joint reliability was evaluated by a high-speed solder ball shear test. Sn-3.0Ag-0.5Cu (SAC305) was used as the solder ball in this study. In the electroless Pd deposition on the electroless Ni film, deposition reaction processes involve replacement reaction and following reduction reaction. We considered that the solder joint reliability was influenced by Pd replacement reaction time and was excellent when replacement reaction time was short. On the basis of the solder joint reliability obtained after multiple reflow cycles and thermal aging, the optimum thickness of the Pd film was found to be 0.05–0.2 μm. The covering property of electroless Pd plating film on the electroless Ni plating film was also investigated. We found that an electroless Pd plating film with a thickness of 0.02 μm or more covered the electroless Ni plating film adequately, and the solder ball joint reliability in this case was better than that with electroless Ni/Au plating. We consider that the shape of the intermetallic compounds (IMCs) is one of the factors that influence the solder joint reliability after multiple reflow cycles. Consequently, we inferred that the high adhesion at the dendrite layers of IMCs/solder interface resulted in excellent solder ball joint reliability after the reflow cycles. We consider that the thickness of the IMCs is one of the factors that influence the solder joint reliability after thermal aging. In (Cu, Ni, Pd) 6 Sn 5 IMCs that contained trace amounts of Pd, the growth of the IMCs is prevented by Pd, resulting in excellent solder ball joint reliability after thermal aging.

An electroless nickel (Ni)/electroless palladium (Pd)/immersion gold (Au) (ENEPIG) surface finish is widely applied to substrates used in various semiconductor packages. However, many issues have been arising in terms of solder joint reliability (SJR) during the assembly process. A number of factors can affect SJR such as thickness of each layer of ENEPIG, reflow profile, plating bath conditions, chemical composition of Pd and Ni layer, and chemical composition of solder balls. This paper focuses on investigating the influence of the factors on SJR and formation of intermetallic compounds (IMCs). The present study investigated the effect of the number of reflows (1, 3 and 5), Ni and Pd thickness of ENEPIG (Ni: 3, 6 and 9 µm, Pd: 0.02, 0.06 and 0.1 µm), chemical composition of Pd layer (pure Pd and Pd-phosphorus (P)) and chemical composition of solder balls (tin (Sn)0.7copper (Cu), SAC305 (Sn3.0 silver (Ag) 0.5Cu), SAC302 (Sn3.0Ag0.2Cu) and Sn3.5Ag). Special focus involved the combination of solder balls (SAC305 and Sn3.5 Ag) and chemical composition of the Pd layer (pure Pd and Pd-P). SJR that were evaluated through pull test and shear test, and then IMCs were observed through scanning electron microscope (SEM) analysis. The effect of Pd and Ni thickness with Pd-P and pure Pd was confirmed. Compared to Pd-P ENEPIG, a relatively high risk of SJR was found when using solder ball with no or low Cu content (e.g., SAC302 and Sn3.5Ag) and pure Pd ENEPIG. As a result of SEM analysis, Kirkendall voids were observed in the Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> SnP IMC layer only on pure Pd ENEPIG with Sn3.5Ag solder balls and the fracture occurred along the void line. For Sn3.5Ag, a thicker P-rich layer (around 700 µm) was formed compared to SAC305 (300µm).

Electrolytic and electroless Ni/Au are common pad surface finishes on area array (BGA or CSP) packages and printed wiring boards (PWB). The electroless nickel/immersion gold (ENIG) process often is implemented when there is insufficient space to allow bussing for the more common electrolytic Ni/Au plating. The ENIG process continues to be used despite evidence that it may cause catastrophic, brittle, interfacial solder joint fractures. In this investigation a plastic ball grid array (PBGA) test vehicle is used to compare quality and reliability of standard and experimentally modified ENIG surface finishes. The standard electrolytic Ni/Au surface finish is used as the control cell for the experiment. Ball shear tests and optical and scanning electron microscopy are performed on as-received and thermally preconditioned packages to evaluate package quality prior to assembly. Accelerated temperature cycling (0/+100/spl deg/C and -40/+125/spl deg/C) is used to evaluate solder joint attachment reliability. Detailed failure mode analysis is used to compare the fracture modes in the ball shear and thermal cycled samples in the electroless and electrolytic packages. The results are discussed in terms of the failure modes and the characteristics of the different Ni/Au surface finishes.

During the last few years, the Solectron Technical Center has conducted a series of CSP board level manufacturing assessment studies on the self-centering effect during reflow and rework, component placement accuracy requirement, and the effects of pad design and surface finishes. Based on the results of these studies, a standard CSP assembly procedure was established. This procedure is being deployed to all Solectron manufacturing sites and is used to assess each site's CSP assembly readiness. This deployment strategy allows the corporate technology group to assess the technical capability of all Solectron sites to fulfill our commitment to enforce common process on the global basis. This paper will describe the methodology used for the deployment of the CSP assembly process. A test vehicle optimized by incorporating all the findings from the studies on pad geometry, solder volume, and surface finish was designed to assess the reliability of CSP after SMT assembly and rework processes. A series of analyses was performed on the test vehicle including the use of the mechanical deflection system designed by IBM to study the reliability of solder joints. Correlation between fatigue resistance, crack pattern, and their impact on the reliability of solder joints were also established. Stress and displacement under external thermal and mechanical fields were simulated. Finite element method was used to analyze the Von Mises stress and strain energy distributions. The impact of package standoff, die size, and DNP on the fatigue resistance and reliability of solder will be discussed.

Intermetallic compound(s) (IMC) that nucleates at the interface between solder and Cu trace during a soldering reaction, is one of the most crucial factors for microelectronic packaging reliability. This study was conducted to modify the IMC microstructure and to reinforce the mechanical strength of Sn–Ag–Cu/Cu microelectronic joints through various surface finish coatings, including organic solderability preservative (OSP), immersion Ag (ImAg), immersion Sn (ImSn), Au/Pd (electroless palladium/immersion gold, EPIG), and Au/Pd/Au (IGEPIG) layer(s). We confirmed that the type of surface finish dominated the IMC growth morphology and mechanical characteristics of the Sn–Ag–Cu/Cu solder joints, even though these surface finishes were eliminated in a few seconds of the soldering process. A dense Cu6Sn5 layer with a scallop-like appearance was obtained for the traditional OSP case, while a prismatic, loose Cu6Sn5 microstructure was produced for the alternative cases (metal films). This loose Cu6Sn5 microstructure offered numerous molten solder channels for the in-diffusion of Sn to Cu, retarding undesired Cu3Sn growth at the Cu6Sn5/Cu interface; consequently, a brittle-to-ductile transition in the joint fracture mode with a high shear strength and fracture energy was obtained in the high-speed ball shear (HSBS) test. A significant mechanical reinforcement of the Sn–Ag–Cu/Cu microelectronic joints can be achieved with the replacement of the traditional OSP coating by the newly developed IGEPIG trilayer surface finish.

This paper documents a chip scale package (CSP) cost analysis using SEMATECH's Cost/Resource Model (CRM). The intent of the analysis was to compare costs between CSPs and conventional package technologies such as the thin small outline package (TSOP) and ball grid array (BGA) to determine whether CSP is a viable packaging technology. The analysis includes costs of both package and board assembly components in a high volume, mature production factory. Four representative CSP types (custom lead frame, flex circuit interposer, rigid substrate interposer, and wafer level assembly) and three traditional surface mount package configurations (plastic ball grid array [PBGA], ceramic ball grid array [CBGA], and thin small outline package [TSOP]) were selected to benchmark. By selecting CSPs across many applications and I/O ranges, the goal was to study a cross section of CSPs that were in or near production. Analysis results indicated that CSPs with a low I/O count are cost-competitive with conventional surface mount packages and can be used with the existing printed circuit board (PCB) infrastructure. However, CSPs with a high I/O count are not currently supported by conventional PCB technology and are not cost-competitive with conventional surface mount package technology.

A two-sided no clean mass reflow process for large plastic ball grid array (PBGA) and plastic quad flat pack (PQFP) packages is presented. Emphasis is placed on the PBGA and PQFP assembly parameters such as the design, materials, and processing of the packages and printed circuit board (PCB), solder paste, stencil printing, pick-and-place, reflow, and inspection. The solder joint reliability of the two-sided PCB assembly is evaluated by shear tests and thermal cycling tests.

Computational stress analysis was performed in this study to investigate the solder joint reliability of plastic ball grid array (PBGA) packages with various configurations. The packages under investigation were 27 mm body‐size, 1.27 mm ball‐pitch, perimeter PBGAs with and without thermal balls at the centre. The diagonal cross‐section of the PBGA‐printed circuit board (PCB) assembly was modelled by plane‐strain elements. The model was subjected to a uniform thermal loading and the solder joints were stressed due to the mismatch of coefficient of thermal expansion (CTE). A total number of 24 cases, involving different solder ball populations, chip sizes, and substrate thicknesses, were studied. The accumulated effective plastic strain was evaluated as an index for the reliability of solder joints. The results of this study revealed the effects of the aforementioned parameters on the solder joint reliability of perimeter PBGA assemblies. The findings are very useful for the design of plastic ball grid array packages.

Soft errors in microelectronics devices, responsible for the malfunction of electronic systems, have become a hot issue for miniaturized and high-density packaging like three-dimensional (3D) packaging. Low alpha solder generates very few α-radiation-caused errors and malfunction in electronic devices compared with regular solder. It can improve performance and reliability of through-Si-via (TSV) packaging, prompting the need to adopt low alpha solder for bumping in TSV packaging. TSV technology has emerged as a popular choice for 3D packaging and chip stacking. In this study, the bonding properties of low alpha solder on Cu-filled TSV were investigated. TSVs were fabricated in a Si wafer by deep reactiveion etching, and Cu was filled in the via by electroplating using the periodic pulse-reverse current waveform. Cu filling in the via was achieved in 4 h without any defects at a cathodic current density of −8 mA/cm2. The LC-3 class of a low alpha solder ball (alpha emission &amp;lt; 0.05 cph/cm2) having a composition of Sn-1.0 wt.% Ag-0.5 wt.% Cu (SAC105) and a diameter of 80 μm was reflowed on the Cu-filled TSV to form the solder bump. High-speed shear test was performed on the bumped low alpha solder ball to assess the shear strength and to investigate the fracture mode. The shear strength of the low alpha solder bump showed a maximum value of 369.63 mN at 1.0 m/s shearing speed and 17.6 μm tip height. The fraction of brittle fracture increased with increasing shearing speed.

In the transition to lead-free, components suppliers need carry the product of lead-free and lead components. This could cause the extensive logistic problems in manufacturing. Therefore, it is necessary to study the solder joint character of Sn-Ag-Cu BGA and Sn-Pb solder paste. In this study, the results of solder joint shape and reliability evaluations of PBGA (Plastic ball Grid Array) lead-free package assembled to PCBs (Printed Circuit Boards) with eutectic Sn-Pb solder paste was presented. The lead-free package was assembled under various reflow profiles and PCB surface finish. The peak temperature of reflow soldering of 210, 225 and 235 °C with the soak profile was used. The PCB surface finish included HASL (Hot Air Soldering Level) and ENIG (Electroless Ni/Immersion Au). The different types of solder joints, both as-reflowed and after reliability test, were examined using optical microscope, transmission X-Ray. The reliability test of TTC (Thermal Torsion Cycling) and ATC (Accelerated Thermal Cycling) was used. Detailed failure analysis will also be presented.

This paper presents an experimental investigation on the solder ball shear strength of plastic ball grid array (PBGA) packages. The emphasis is placed on showing the effect of room temperature aging on the degradation of solder ball shear strength. The specimens under investigation are standard commercial PBGA packages with 63Sn-37Pb eutectic solder balls. The specimens are subject to various lengths (up to 72 hours) of room temperature aging after the reflow. Afterwards, ball shear tests are performed to evaluate the solder ball shear strength. The experimental results show that the solder ball shear strength may drop up to 10% within 3 days of room temperature aging. The outcome of the present study may give a general guideline for the meaningful comparison of solder ball shear strength.

In the present study, a facility, i.e., a mechanical deflection system (MDS), was established and applied to assess the long-term reliability of the solder joints in plastic ball grid array (BGA) assembly. It was found that the MDS not only quickly assesses the long-term reliability of solder joints within days, but can also mimic similar failure mechanisms in accelerated thermal cycling (ATC) tests. Based on the MDS and ATC reliability experiments, the acceleration factors (AF) were obtained for different reliability testing conditions. Furthermore, by using the creep constitutive relation and fatigue life model developed in part I, a numerical approach was established for the purpose of virtual life prediction of solder joints. The simulation results were found to be in good agreement with the test results from the MDS. As a result, a new reliability assessment methodology was established as an alternative to ATC for the evaluation of long-term reliability of plastic BGA assembly.

Characterization of the shear test method with low melting point In–48Sn solder joints

The automotive industry has been slow to adopt the usage of BGA devices, largely due to concerns with solder joint reliability under harsh conditions. For example, some onengine applications require surviving −40 to +150°C thermal cycling. The plastic ball grid array (PBGA) has proven itself able to meet these requirements, allowing the automotive industry to take advantage of the high assembly yields these devices offer. This paper summarizes the modeling and testing experience of one automotive supplier, including the effects of circuit board thickness, solder voids, conformal coating, and dual reflow on reliability.