Leadframe Surface Research Articles

Influence of Material Properties on Ruggedness Evaluation of Package Architectures for SiC Power Devices

Button shear tests at different temperatures between different mold compounds and Cu-leadframes have been performed to evaluate the adhesion of mold compounds to the inner surfaces of SiC-power devices. The results at different temperatures show the behavior of different material and layer stack combinations under storage at room temperatures as well as under operating conditions with elevated temperatures, where adhesion and thus the hermeticity of the device against moisture is significantly lowered. It has been shown that different thermomechanical properties of the mold compounds as well as the usage of different adhesion promoter materials have a significant effect on the adhesion properties of the mold compound to the leadframe surface of the SiC power devices, which have direct impact on the ruggedness and lifetime stability. Furthermore, these results have been correlated to thermomechanical simulations of the package architecture of SiC power devices under stress. Different wire bond architectures have been evaluated in simulations with and without die top delamination taken into account, showing that EMC delamination may play a major role in the lifetime stability of SiC power devices under thermomechanical stress like simulated in TCT- , IOL- and PTC-testing.

Development of an ultrasonic-assisted soldering system for Fe-based lead frame surface coating

Development of an ultrasonic-assisted soldering system for Fe-based lead frame surface coating

Cascaded detection method for surface defects of lead frame based on high-resolution detection images

In the field of semiconductor production and manufacturing, the detection of defects on lead frame surfaces is a vital process. This process plays a key role in ensuring the quality of the final product. Using high-resolution detection images to detect multi-scale tiny surface defects is necessary, but this amplifies the impact of environmental noise. Therefore, suppressing both the false negative rate and false positive rate in practical detection scenarios is a challenge that needs to be overcome. Current research on lead frame surface defect detection is mostly concentrated on the downloaded standard original images, which limits its application in actual production lines. This paper presents a cascaded detection method for surface defects of lead frame based on high-resolution detection images. Firstly, this study presents the unit cell extraction module to convert the detection object from high-resolution image to hundreds of unit cells. The proposed module can handle real-time detection images in the production pipeline, especially addressing situations such as lighting imbalances and tilted detection images. Subsequently, this study proposes a lead frame surface defect detection network (LDD-net), which takes unit cells as inputs and can effectively detect multi-scale defects. Compared to other models, LDD-net can effectively capture the features of subtle defects. Additionally, this paper introduces the deviation in the central width direction into the CIoU localization loss, enhancing the accuracy of defect localization in LDD-net. The data set is constructed using the machine vision detection system and conducts training and testing. Specifically, experiments of LDD-net on the data set obtained 85.01% mean average precision (mAP) and 37 ms of inference time, respectively. The detection accuracy exceeds 95%, and the false negative rate can be controlled below 6%. This approach will assist manual monitoring personnel in evaluating product quality.

Sulfur Ingression on Encapsulated Leadframe of Discrete Semiconductor Package

Methanesulfonic acid (MSA) has been widely used in the electroplating step at a backend semiconductor assembly process. This process comes after component encapsulation, which serves primarily to protect internal components of a device as well as to prevent ingression of chemical byproducts. The objective of this article is to study sulfur (S) ingression activities with respect to both electroplating and encapsulation processes and their effect on leadframe surface conditions. This can be achieved through observation of leadframe surface condition on samples prepared through laser ablation or mechanical decapsulation. Results from 17 engineering lots show that 25% of samples analyzed were observed with leadframe surface irregularities. The energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the trace of S element on the area with surface irregularities, which can be linked to S ingression based on the trace of its path from outside, probably due to the existence of a microgap on the package. These findings provide a clearer understanding of the ingression path of S for encapsulated copper (Cu) leadframe. Even though ingression of S does not directly cause a failure, it is thought that this could act as a precursor to further failure mechanisms such as corrosion-like phenomena.

Influence of Textured Nickel/Palladium/Gold-Silver (Ni/Pd/Au-Ag) Layer on Pre-plated Leadframe for Automotive Applications

High quality and reliability of integrated circuit packaging is required for automotive applications due to the safety concerns. Therefore, elimination and controlling the package defects which can lead to reliability failure is essential. One of the defects that leads to reliability issue is delamination. This study presents the influence of textured leadframe surfaces on the surface wettability and delamination occurrence in automotive package unit. Standard bare Cu leadframe was used as comparison. The leadframe surface was textured with Ni/Pd/Au-Ag using electroplating technique. The surface morphologies of both bare and textured leadframe were characterized using field-emission scanning electron microscope and optical profiler. The energy dispersive spectroscopy was used to quantify the elemental composition of the samples. All samples went through the wettability test under two conditions, which were room temperature and 175°C. The reliability test of complete package was subjected to moisture sensitivity preconditioning level 1 according to IPC/JEDEC STD 020 and the baking process was performed at 125°C for 24hrs followed by soaking process under the condition of 85°C and 85 of relative humidity. Scanning acoustic tomography according to IPC/JEDEC STD 035 was performed after three cycles of infrared reflow at 260°C. Higher surface roughness was observed for pre-plated leadframe (PPF) compared with bare leadframe. The lowest value of average contact angle (∼55°) was observed for PPF at 175°C indicated better wettability feature. Furthermore, no delamination occurrence was observed for PPF sample compared with bare copper leadframe. The obtained result reveals that leadframe with textured surface of Ni/Pd/Au-Ag improved interfacial surface adhesion which eliminated the delamination defect and thus improved the package robustness and reliability.

Miniaturized Stacked Die QFN for Tire Pressure Monitoring System Applications

Tire Pressure Monitoring Systems (TPMS) are electronic wireless systems that monitor and report air pressure inside pneumatic tires in real time. An example of a TPMS module integrated with the valve stem and showing the typical tire mounting location is shown in Figure 1. For their safety and fuel economy benefits, starting with the mid-2000's, active TPMS were mandated on many vehicles worldwide. The NHTS estimates that there are approximately 23,000 accidents and 535 fatalities annually involving tire underinflation and blowouts [1]. The use of TPMS has been shown to result in improved fuel economy and therefore reduced carbon emissions [2]. TPMS in passenger vehicles was mandated in the US as of Sept. 1, 2007 under the TREAD Act, in the European Union as of Nov. 1, 2012 and in South Korea as of Jan.1, 2013. Countries like Russia, Indonesia, the Philippines, Israel, Malaysia, Turkey and many others soon followed [3].
 The first TPMS systems were large and bulky with a significant electronics content [4]. Since that time TPMS electronics have gotten more energy efficient and form factors have come down dramatically. This paper will outline an effort to miniaturize an existing 1.0 mm pitch, 7x7x2.2 mm body size 24 lead QFN (Quad Flat No Leads) TPMS down to a 4x4x1.98 mm body size QFN with 0.5 mm pitch that would still meet automotive AEC Grade 1 reliability requirements. The original 7x7 mm three die QFN package consisted of an ASIC, a pressure sensor and an accelerometer. This miniaturization led to many technical challenges at both the package and board level. This paper will primarily address the board level reliability (BLR) challenges encountered due to the large silicon to package ratio along with the 50% reduction in pitch. Through a series of test vehicles with variables such as QFN leadframe surface finish, lead shape and size, wettable flank (WF) technology and anchors pads, the BLR was successfully improved to the point where it met application requirements.

Package Reliability and Integrity Improvements for a Thermally Enhance Non-Conductive Die Attach Adhesive for ASIC Devices on Exposed Pad Packages

Abstract Polymers being used in a plastic-encapsulated integrated circuit (IC) package exposed to a humid environment absorbed moisture and expand resulting to a so called delamination failure. Weak or imperfect adhesions between the interfaces of the mold compound and adhesive unto the leadframe surface are often the main sources of these failures. In response to automotive requirements and to ensure excellent package reliability and integrity, delamination in all interfaces should then be eliminated. Thus the primary objective of this work is to fulfill the no delamination criteria in all interfaces after moisture soak for an exposed pad package. To satisfy these requirements, activities includes leadframe design improvements, surface enhancement and bill-of-material changes. With the design improvements implemented, still the material compatibility plays an important role in achieving improved package reliability.

Oxidation characteristics of commercial copper-based lead frame surface and the bonding with epoxy molding compounds

This study investigates surface oxidized layers of Cu-Fe-Zn-P (C194) and Cu-Ni-Si-Mg (C7025) lead frames under different oxidation conditions and their influence on the adhesion of epoxy molding compounds with lead frames. Micro-etching and electroplating are adopted to roughen the surface. Isothermal heat treatments which simulate molding and curing processes, as well as high temperature aging, are carried out to oxidize lead frame surface. According to the absorption peaks of FTIR (Fourier transform infrared spectroscopy) spectra, the topmost surface of the oxide layer can be easily identified. In combination with the reduction potential and time obtained from the coulometric reduction test, the variation of oxide phases along the through-thickness direction can also be revealed. Experimental results show that in addition to surface roughness, surface oxides and their thickness play more important roles in the interfacial strength between lead frames and epoxy molding compounds. In the case of the surface with one single Cu2O layer, an increase in oxide layer results in a decrease in bonding strength. Once the topmost surface forms CuO, the bonding strength could be enhanced due to a greater surface energy. Compared with electroplated C194, the thinner surface oxide layer and thus better performance in adhesion strength for electroplated C7025 can be ascribed to the immersion Ag surface treatment.

Process factors affecting adhesion of encapsulation molding compounds

PurposeThe purpose of this paper is to determine the key process factors which affect the adhesion strength of encapsulation molding compounds (EMCs) to leadframes to obtain reliable components without any need to pretreat the leadframe surface.Design/methodology/approachEMCs were molded to Cu leadframes to experimentally quantify the effect of mold temperature, resin viscosity, leadframe oxidation and powder moisture on the adhesion force. Component reliability was assessed by PCT.FindingsA higher mold temperature result in a larger adhesion force. The mold temperature of 175°C provides the largest process window. Leadframe oxidation can increase adhesion first, but then decrease it drastically with further oxidation. The powder moisture content has mixed effect on adhesion.Practical implicationsBy molding at 175°C, limiting the wire bonding time and minimizing the powder moisture content, reliable components can be obtained without any need for leadframe surface pretreatment such as plasma cleaning or surface coating.Originality/valueQuantify the key process factors which affect the adhesion of EMCs and reveal reason behind the current industrial practice of using the mold temperature of 175°C.

Improvement of the Adhesive Strength of the Leadframe and Epoxy Resin by Forming Organic Molecules–Metal Composite Interface

SUMMARYDelamination in semiconductor plastic package is a cause of reliability degradation. We have tried to improve the adhesion strength between leadframe and epoxy resin. In this study, organic molecules–metal (Cu) complex “EC tag (Cu)” were employed. It is immobilized on the leadframe surface as adhesion promoter to adhere with thermosetting epoxy resin. In the results, immobilized EC tag (Cu) act as adhesion promoter that shows greater adhesion between leadframe and epoxy resin. Also, the leadframe with adhesion promoter doesn't affect semiconductor assembly characteristics.

Mechanical Interlocking on Leadframe Surface for Bondability of Au Wedge Bond

This work is a contribution towards the understanding of wire bond integrity and reliability in relation to their microstructural and mechanical properties in semiconductor packaging.The effect of surface roughness and hardness of leadframe on the bondability of Au wedge bond still requires detail analysis. Two type of leadframes namely leadframe A and leadframe B were chosen and scanning electron microscope (SEM) and optical microscope were used to inspect the surface morphology of leadframes and the quality of created Au wedge bond after wire bonding process. It was found that there were significant differences in the surface morphologies between these two leadframes. The atomic force microscopy (AFM) which was utilized to measure the average roughness, Ra of lead finger confirms that leadframe A has the highest Ra with value of 166.46 nm compared to that of leadframe B with value of 85.89 nm. While hardness value of different lead finger from the selected leadframe A and B obtained using Vicker microhardness tester are 180.9 VH and 154.2VH respectively.

Effect of the Ni/Pd/Au-Cu pre-plated finish lead frame surface structure treated by various surface roughening methods on packaging properties

Two roughening methods involving micro-etching and mixed mode etching of pre-plated finish (PPF) surfaces were used to examine the nickel-coated layer thickness effect on the surface morphology. The PPF lead frames treated by micro-etching (ME) surface roughness drastically decreased with increased nickel-coated layer thickness, while the PPF lead frames treated by mix mode roughening (MMR) maintained comparatively good surface roughness even with thick nickel-coated layers. The shear strength of the PPF of a lead frame treated by ME and MMR reached up to five times that of the untreated PPF based on a moisture sensitivity level button shear test. The failure mechanism of the PPF lead frame treated by ME was the formation of cracks through the interface between the lead frame and the epoxy molding compound, which led to the breakage. An experimental basis is provided for the application of PPF lead frames, as well as a theoretical foundation for increasing the adhesion strength of rough surfaces. Therefore, this study is of great theoretical and practical significance.

Investigation on Some Parameters Affecting Optical Degradation of LED Packages During High-Temperature Aging

The mechanism of optical degradation for the light emitting diode (LED) packages in the light bars under the high-temperature aging condition, one of the accelerated life tests, is studied experimentally and numerically. Some parameters, including junction temperature, encapsulant materials, delamination, leadframe surface degradation, and encapsulation, are closely investigated. It is found that the encapsulants (with or without phosphors) and interface delamination have no effect on the optical degradation during the high-temperature aging. On the contrary, junction temperature, leadframe surface degradation, and encapsulation play important roles on this degradation. Optical degradation of the LED packages is found to be mainly caused by silver chloride, which is generated on the leadframe surfaces with an exposure of silver finish in light and heating conditions after interface delamination happening during the high-temperature aging. The high junction temperature could speed up the generation of silver chloride. Moreover, the blue LED package with an encapsulant (silicone) surprisingly give a lower lumen maintenance than one without encapsulant during the high-temperature aging, because of more light absorption on the darkening leadframe surface by total light reflection from silicone encapsulant. Some important parameters affecting the thermal reliability of the LED packages have been identified and the corresponding optical degradation mechanism has been clarified.

リング状光源を用いたICリードフレーム表面の欠陥検査システムの開発

リング状光源を用いたICリードフレーム表面の欠陥検査システムの開発

エポキシ樹脂との接着強度向上を目指したリードフレーム表面のナノ形状制御

エポキシ樹脂との接着強度向上を目指したリードフレーム表面のナノ形状制御

Study on Ag-Plated Cu Lead Frame and Its Effect to LED Performance Under Thermal Aging

A systematic study about the effect of thermal aging time on lead frame morphology and LED optical performance was demonstrated in this paper. Three different lead frames for LED manufacturing were chosen to execute thermal aging test for reliability qualification. An evolution about Ag recrystallization, Cu diffusion, Cu nucleation, and growth on lead frame surface was comprehensively explained. The relationship between surface morphology and lead frame reflectance was first established by experimental characterization and comparison. After that, the- oretical analysis based on diffusion theory reasonably explained the copper diffusion and nucleation process, which matches well with the morphology changes. Later on, optical simulation on various commercial LED packages was implemented to evaluate the effect of lead frame reflectance on the optical output. In conclusion, centering on Cu diffusion induces reflectance decrease, the connection initializes from thermal aging to final LED lumen performance was successfully built up in this paper. The findings can be directly applied as guidance to facilitate industrial LED manufacturing and reliability qualification.

Smart Power Module Molding Advances: Evaluating high temperature suitability of Molding Compounds

During the last years within power electronics packaging a trend towards compact power electronics modules for automotive and industrial applications could be observed, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics yielding maximum miniaturization. Transfer molding is the method of choice for cost effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package: Typically those packages are asymmetric, a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed providing a heat path for optimized cooling. This asymmetric geometry is prone to yield warped substrates, preventing optimum thermal contact to the heatsink and also putting thermo-mechanical stress on the encapsulated components, possibly reducing reliability. Such packages being truly heterogeneous, combining powerICs, wire bonds, SMDs, controlICs, substrate and leadframe surfaces, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally those packages need to operate at elevated temperatures for long time, e.g. operate at 200 °C for 1000 h and more, so high thermal stability is of ample importance. Within this paper the main goal is to identify transfer molding compounds suitable for the encapsulation of smart power modules, ready to be used at 200 °C and determine the actual maximum temperature of use of such high performance molding compounds currently available in the market. Summarized a detailed description of the high temperature suitability of high performance molding compounds is provided – additionally an extended test methodology is described to facilitate future material evaluation for HT or harsh environment use of polymeric materials as encapsulants or base materials.

Transfer Molding Technology for Smart Power Electronics Modules: Materials and Processes

In recent years, within power electronics packaging, there has been a trend toward compact power electronics modules for automotive and industrial applications, where a smart integrated control unit for motor drives is replacing bulky substrates with discrete control logic and power electronics. Most recent modules combine control and power electronics, yielding maximum miniaturization. Transfer molding is the method of choice for cost-effective encapsulation of such modules due to robustness of the molded modules and moderate cost of packaging. But there are challenges with this type of package. Typically, these packages are asymmetric, and thus a substrate with single sided assembly is overmolded on the component side and the substrate backside is exposed, providing a heat path for optimized cooling. This asymmetric geometry is prone to yielding warped substrates, preventing optimum thermal contact to the heat sink and also putting thermomechanical stress on the encapsulated components, possibly reducing reliability. Such packages are truly heterogeneous, combining power ICs, wire bonds, SMDs, control ICs, substrate, and lead frame surfaces. As a result, the encapsulant used needs to adhere sufficiently to all surfaces present. Additionally, those packages need to operate at elevated temperatures for extended time periods, for example, at 150°C for 2000 h and more, so high thermal stability is of prime importance. Within this paper, a reference application is described integrating power and control logic inside a lead frame based molded package. Taking into account the challenges mentioned above, a detailed description of material selection for this module will be given, including material analysis, such as rheology, reactivity, and change in εr; and thermomechanical properties, in initial stage as f(t,T) and after media storage. Process development tools for module molding are used to ensure manufacturability and usability. Concluding rules for encapsulant material selection and package setup are provided.

Cu diffusion in Ag-plated Cu leadframe packages

Cu diffusion onto an Ag-plated Cu leadframe surface was detected by Energy Dispersive X-ray (EDX) after de-capsulating the molded package. However, no Cu was detected by EDX on the Ag surfaces of bare leadframe, leadframe after die attachment including die attachment curing, or leadframe after wire bonding. Temperature simulation of molding and post-molding curing show that the temperature and its duration have some impact on the Cu diffusion, which is as expected. Interestingly, this study shows that the Cu diffusion onto the interface of the Ag-plated surface and mold compound is very much dependent on the type of mold compound used, which has never been reported in the literature so far. The Cu diffusion was detected by EDX only for certain types of mold compounds used. It is concluded that the mold compound is a major contributor to the Cu diffusion observed. This is possibly because S and O in the mold compound react with Cu and form copper sulfides and copper oxides, which accelerate the Cu diffusion from the Cu leadframe substrate onto the interface of the Ag surface and mold compound.

Shelf-Life Study of Ag/NiNiP-Plated Cu Leadframes Without Anti-Tarnish Coating

An Ag spot/full nickel and nickel phosphorus (NiNiP)-plated Cu leadframe without the anti-tarnish layer was used for aluminum wire bonding in power packages. Two periods of shelf-life, namely 7 months and 13 months, of the leadframe were studied in terms of processability (die attachment and wire bonding) and package reliability. It was found that the leadframe with 7-month shelf-life showed positive results for both processability and package reliability. The leadframe with 13-month shelf-life showed positive results for processability. However, it showed delamination at the leads between the NiNiP leadframe surface and the molding compound interface after high-temperature storage for 1000 h. Further analysis showed that the delamination is related to Ni diffusion into the interface of the NiP/molding compound and S in the molding compound during the reliability test.