Reliability analysis of SiP module board level bending test

We report board level stress tests of leadless QFN packages (pitch 0.5 mm) with focus on different application fields. We did temperature cycling tests, drop test, bend test, and power cycling tests, with special focus on the influences of board design and soldering technology. We performed the stress tests until end-of-life and determined the dominating failure modes. In our temperature cycling study on 2.35 mm thick boards solder joints of SnAgCu performed slightly worse than SnPbAg. We were able to optimize the thermal pad design on the PCB to improve the temperature cycling reliability. For drop test we achieved an excellent reliability by comparing different board designs. This was achieved by avoiding copper trace cracking within the board. This failure mode we verified also with cyclic bend tests. Additionally we performed power cycling investigations using different power consumptions and solder pastes for board assembly (SnAgCu and SnPbAg). A strong lifetime dependence on power and a superior behavior of SnAgCu solder was found. The results were successfully correlated with finite element simulations. In our stress tests we observed clear evidence for influence of soldering technology and board design/technology on board level reliability performance. For different application fields satisfactory reliability can be achieved in case specific measures on board assembly and printed circuit board design are taken

Mechanical durability of screen-printed flexible silver traces for wearable devices

Materials characterization of the effect of mechanical bending on area array package interconnects

Solder joints between a package and a printed wiring board (PWB) of a portable electronic device sustain thermal cycling as a result of power on-off, cyclic bending by key pad operation, and impact bending by dropping. Therefore, the authors conducted heat cycling, cyclic bending, and cyclic impact bending tests on the ball grid array solder joints between a chip scale package and a PWB. The evaluated solders were Sn-3 Ag-0.5 Cu and Sn-37 Pb. The tests showed that the life cycles of the Sn-3 Ag-0.5 Cu solder joints for the feat cycling and cyclic bending tests were approximately twice those of the Sn-37 Pb solder joints. On the other hand, in the case of cyclic impact bending test, the life cycle of the Sn-3 Ag-0.5 Cu joint under large strain was smaller than that of the Sn-37 Pb solder joint because of interfacial crack growth between the solder and the PWB. These fatigue lives of the joints were compared with crack initiation and failure lives of plain specimens by calculating local strain ranges in the joints by elastic plastic finite element analysis.

In this study, the board level reliability (BLR) performance of different copper (Cu) post wafer level package (WLP) structures without epoxy or molding encapsulation have been evaluated and compared to standard WLP. The Cu post WLP test vehicle has been performed on different stack up structures of 4.7 x 7.1 mm2 package size at 0.4 mm ball pitch. The Cu post bumps of test vehicles were manufactured through main-stream production technologies including standard ball drop and electro-plated lead free solder after Cu post completed. The Cu post WLP will enhance the risk of board level solder joint fatigue due to thick Cu post without encapsulation will increase bump site stress. The optimized design parameters of package stack up with low temperature cured polyimide are implemented to accommodate the increased stress. In this work, we also evaluated a novel Cu post WLP stack up structure for fast package cycle time and fine pitch application. The improved BLR performance of large die size Cu post WLP is demonstrated in this investigation. The failure modes analysis and Weibull failure statistics are presented for the BLR results and recommendations as to the preferred Cu post WLP structure are also included.

In this study, finite element analysis (FEA) was used to simulate a thermal cycling test result for a PBGA assembly with Sn-3.8Ag-0.7Cu solder joints subject to thermal cycling of -40°C to +125°C. The PBGA assembly was modeled using a 3D-quarter 1/8th octant model of the PBGA assembly. Two constitutive models for the SAC387 solder were investigated using the Anand Viscoplastic (AV) model and elastic-plastic-creep (EPC) model. Low cycle fatigue life prediction based on non-linear Plastic work (PLWK) and inelastic strain energy density (SED) were used to predict the thermal cycling fatigue life and compared to the test results. Volume averaging studies are needed to quantify the effect of the volume of elements selected on the non-linear Plastic work (PLWK) and inelastic strain energy density (SED), and fatigue life results

Package on package (POP) technologies are advancing to finer pitches to account for technology advances in mobile applications along with leaving memory flexibility to the customer. As POP technology advances to finer pitches, more emphasis is placed on the top and bottom packages to reduce the overall height, physical dimensions, and package complexity. An area of main concern is for the top package pitch reduction moving away from 0.5 mm to 0.4 mm to achieve the desired POP package. This paper discusses the technical achievements developed for 0.4 mm POP SMT builds as it relates to reflow conditions along with warpage characteristics. We also discuss the development of the 0.4 mm bottom package in relation to top ball processing by means of laser ablation and associated solder attached to the top package. We also provide information on 0.4 mm SMT build characteristics and the associated board level reliability (BLR) for the combined package. The BLR data includes temperature cycling of -40°C to 125°C for 2000 cycles at 10 minute dwells, 200 drop shocks, and 100,000 cyclic bend tests on JEDEC designed daisy chain boards.

Fatigue strength estimation of a CF/PEKK composite through self-heating temperature analysis using cyclic bending tests at 20 kHz

Clinching is a mechanical joint for fastening sheet metal components, and it is widely used in automotive industry. In this paper, the application of mechanical clinching to a built-up aluminum beam is studied. At first, tensile-shear tests and fatigue tests are carried out on clinched joints of 6063-T5 aluminum alloy sheet to investigate the tensile-shear strength and fatigue strength. Then, based on the joint strength results of clinched joint, the joint pitch of the built-up beam is designed under the specified bending load. Lastly, static bending test and cyclic bending test are carried out on the built-up beam to investigate the deformation behavior and the flexural rigidity. It is found that load-deflection relation and load-bending stress relation of the built-up beam are equal to those of one type beam calculated using Euler-Bernoulli beam theory. The built-up beam is proved to have the same flexural rigidity as that of one type beam. Cyclic bending test results show that cyclic loading gives no influence to clinched joints and the flexural rigidity of the built-up beam. All results demonstrate that mechanical clinching is an effective connection method in a built-up beam.

Fan-Out Wafer Level Packaging (FO-WLP) technology has been developed in recent years to overcome the limitations of Fan-in WLP (FI-WLP) packages and to add more functionality to WLP. Fan-Out packages expand the WLP market to higher pin count devices and add multiple die System in Package (SiP) capability. In this paper, a novel approach to low cost fan-out packaging based on polyimide flex circuits and wafer level Embedded Die Customization (EDC) is discussed. ChipletT refers to Fan-Out packaging. ChipsetT refers to System in Package developed with WABE (Wafer and Board Level Embedding) technology. WABE technology is based on co-lamination of multi layer polyimide flex wiring and conductive z-axis sintered metal interconnections. Using WABE technology, ultra thin fan-out packages (0.4mm) can be fabricated with lower processing costs, higher throughput and with 3D extendibility. Embedded Die Customization is performed at the wafer level and involves optimization of the die-to-embedding process by using optimized wafer level processing capabilities including polymer processing, copper plating and wafer thinning. Reliability of the ChipletT packages, both component level and board level is evaluated. ChipletT packages show high reliability in component level testing and board level testing (Thermal Cycling and Drop Testing). The thermal performance of ChipletT packages were also evaluated in this study. Thermal resistance parameters θja and θjc were simulated with and without thermal vias for both face up and face down configurations. ChipletT provides a new low cost fan out packaging option with proven component level and board level reliability performance.

Demand for higher levels of integration with cost effective solution have driven the increased use of and innovation in System in Package module for Radio Frequency (RF) new products. System in Package (SiP) module high integration capability allows for wide range of power and frequency applications ranging from low power remote heads to massive Multiple-Input Multiple-Output (MIMO) systems. System in Package module employs both active devices and passive components, such as inductor, capacitor and resistor, together with other materials like substrate, solder and gold wire. This paper discusses the characterization study of solder extrusion during the development work for a new product employing new substrate plating. The study covered two characterization activities on key factors affecting solder extrusion under inductors namely, material characterization and process characterization. Materials characterization covered the study of new substrate plating and the inductor type considered under the new product which may impact solder extrusion. Process Characterization covered the study of solder paste screen print process versus their solder extrusion output response. Characterizations resulted to the definition of optimum pre-mould plasma cleaning parameter and solder screen printing process parameters for the new product, the results of which were integrated in its further development, qualification and production release.

The tunnel lining will be subjected to the cyclic action of high ground stress during service. However, there is a lack of research on the damage evolution mechanism of sprayed engineered cementitious composites (ECC) under cyclic loading. Herein, we studied the strain rate effect and fatigue damage evolution mechanism of sprayed ECC by conducting compression and bending tests at different quasi-static strain rates and high-stress cyclic loading-unloading compression and bending tests. The results show that with the increase of strain rate, the compressive peak stress and bending strength of sprayed ECC show an upward trend, as well as the increase of the change rate. At 8.3 × 10−3 s−1, the compressive SGF is 1.52, with an energy storage limit density of 0.501MJ/m3. At 2.1 × 10−2 s−1, the bending SGF is 1.52, with a peak fracture energy of 49.29 J. In addition, under the compression test, the tensile shear failure of specimens develops from finer double shear planes to coarser multiple shear planes. Under the bending test, the position of the main crack of specimen is gradually transferred from the mid-span to both sides. Under high stress cycle test, the input energy and dissipation energy of the two tests have the similar trend, showing “U” type. The variation of elastic energy and dissipation energy conversion rate exhibits a “U” type with different directions. At the last loading, the dissipation energy conversion rate of compression test is 46.8%, while that of bending test is 70.4%. The damage variable of specimen increases significantly with the increase of the number of cycles, accompanied by an increase in the degree of breakage. In addition, the damage variables based on deformation characteristics are higher than those based on energy characteristics.

The major concerns posed by system-in-package (SiP) designs for network applications are the interconnection reliability between the memory plastic ball grid array (PBGA) package and the SiP module, which we refer to as 2nd-level interconnection, and between the SiP module and the system board, which we refer to as 3rd-level interconnection, induced by thermomechanical stress to the large SiP module, i.e., 55 × 55 mm2 package body size. In this paper, finite element analysis (FEA) and design of experiment (DOE) case studies were used to evaluate the 2803-pin flip chip SiP (FCSiP) and to determine the best construction of the SiP module and optimize the assembly material set. Heat spreader (lid) thickness, heat spreader material, and under-fill implementation were considered in the stress and fatigue lifetime FEA case studies and long-term solder joint reliability, which was accelerated thermal cycle (ATC) tested at operating temperatures from 0 to 100°C. Another important factor in the system-level reliability is an external heat sink, and its compressive force effect was also investigated in the ATC test. In addition, short-term mechanical reliability tests, such as the 4-point monotonic bend test based on the IPC-9702 specification and mechanical shock test based on the JESD22-B110A standard, were also evaluated for the 2803-pin FCSiP qualification. Finally, the results of these experiments were compared with the FEA data in a correlation process.

The recent development of new lightweight sheet metal materials, like advanced high-strength steels or aluminium alloys, in combination with an increasing component complexity provides new challenges to the numerical material modelling in the FEM based process design. An auspicious approach to improve the quality of the numerical results – most notably in springback analysis – is the modelling of the so called Bauschinger effect achieved through implementation of kinematic hardening models. Within this paper the influence of the stress state and the level of pre-strain on the numerical simulation result of the advanced high strength steel DP-K45/78+Z will be analysed. For this purpose, a parameter identification of the kinematic hardening law according to Chaboche and Rousselier is performed at different pre-strains on the basis of experimental data from tension-compression tests as well as cyclic shear tests. Finally, the identified parameters are validated in a comparison between numerical and experimental results of a cyclic bending test.

Visualization of Thermal Effects in Polypropylene-based Composites under Cyclic Bending Tests