Technical Library | 2007-01-31 15:17:04.0
The goal of this project is to evaluate the reliability of lead-free BGA solder joints with a variety of different pad sizes using several different BGA rework methods. These methods included BGAs reworked with both flux only and solder paste attachment techniques and with or without the use of the BEST stay in place StencilQuick™. The daisy chained test boards were placed into a thermal test chamber and cycled between -25ºC to 125ºC over a 30 minute cycle with a 30 minute dwell on each end of the cycle. Each BGA on the board was wired and the continuity assessed during the 1000 cycles the test samples were in the chamber.
Technical Library | 2014-06-19 18:13:23.0
For high-density electronic packaging,the application of flip-chip solder joints has been well received in the microelectronics industry. High-lead(Pb) solders such as Sn5Pb95 are presently granted immunity from the RoHS requirements for their use in high-end flip-chip devices, especially in military applications. In flip-chip technology for consumer electronic products, organic substrates have replaced ceramic substrates due to the demand for less weight and low cost. However, the liquidus temperatures of high-Pb solders are over 300°C which would damage organic substrates during reflow because of the low glass transition temperature. To overcome this difficulty, the composite solder approach was developed...
Technical Library | 2021-01-13 21:34:29.0
Package-on-Package (PoP) is a popular technology for fabricating chipsets of accelerated processing units. However, the coefficient of thermal expansion mismatch between Si chips and polymer substrates induces thermal warpage during the reflow process. As such, the reflow temperature and reliability of solder joints are critical aspects of PoP. Although Sne58Bi is a good candidate for low-temperature processes, its brittleness causes other reliability issues. In this study, an in-situ observation was performed on composite solders (CSs) made of ...
Technical Library | 2019-03-06 21:26:14.0
Electronic assemblies use a large variety of polymer materials with different mechanical and thermal properties to provide protection in harsh usage environments. However, variability in the mechanical properties such as the coefficient of thermal expansion and elastic modulus effects the material selection process by introducing uncertainty to the long term impacts on the reliability of the electronics. Typically, the main reliability issue is solder joint fatigue which accounts for a large amount of failures in electronic components. Therefore, it is necessary to understand the effect of polymer encapsulations (coatings, pottings and underfills) on the solder joints when predicting reliability.This paper presents the construction and validation of a thermo-mechanical tensile fatigue specimen. The thermal cycling range was matched with potting expansion properties in order to vary the magnitude of tensile stress imposed on solder joints
Technical Library | 2018-08-29 21:17:53.0
No-clean solder pastes are widely used in a number of applications that are exposed to wide variations in temperature during the life of the assembled electronics device. Some have observed that cracks can and do form in flux residue and have postulated that this is the result of or exacerbated by temperature cycling. Furthermore, the potential exists for the flux residue to soften or liquefy at elevated temperatures, and even flow if orientated parallel to gravity. In situations such as in automotive electronics, where significant temperature cycling is a reality and high reliability is a must, concern sometimes exists that the cracking and possible softening or liquefying of the residue may have a deleterious effect on the electrical reliability of the flux residue. This paper will attempt to address this concern.
Technical Library | 2019-10-16 23:18:15.0
Despite being a continuous subject of discussion, the existence of voids and their effect on solder joint reliability has always been controversial. In this work we revisit previous works on the various types of voids, their origins and their effect on thermo-mechanical properties of solder joints. We focus on macro voids, intermetallics micro voids, and shrinkage voids, which result from solder paste and alloy characteristics. We compare results from the literature to our own experimental data, and use fatigue-crack initiation and propagation theory to support our findings. Through a series of examples, we show that size and location of macro voids are not the primary factor affecting solder joint mechanical and thermal fatigue life. Indeed, we observe that when these voids area conforms to the IPC-A-610 (D or F) or IPC-7095A standards, macro voids do not have any significant effect on thermal cycling or drop shock performance.
Technical Library | 2015-02-19 16:54:34.0
Pad cratering is an important failure mode besides crack of solder joint as it’ll pass the regular test but have impact on the long term reliability of the product. A new pin pull test method with solder ball attached and positioning the test board at an angle of 30º is employed to study the strength of pad cratering. This new method clearly reveals the failure mechanism. And a proper way to interpret the finite element analysis (FEA) result is discussed. Impact of pad dimension, width and angle of copper trace on the strength is included. Some findings not included in previous research could help to guide the design for better performance
Technical Library | 2015-07-14 13:19:10.0
Bottom terminated components (BTC) are leadless components where terminations are protectively plated on the underside of the package. They are all slightly different and have different names, such as QFN (quad flat no lead), DFN (dual flat no lead), LGA (land grid array) and MLF (micro lead-frame. BTC assembly has increased rapidly in recent years. This type of package is attractive due to its low cost and good performance like improved signal speeds and enhanced thermal performance. However, bottom terminated components do not have any leads to absorb the stress and strain on the solder joints. It relies on the correct amount of solder deposited during the assembly process for having a good solder joint quality and reliable reliability. Voiding is typically seen on the BTC solder joint, especially on the thermal pad of the component. Voiding creates a major concern on BTC component’s solder joint reliability. There is no current industry standard on the voiding criteria for bottom terminated component. The impact of voiding on solder joint reliability and the impact of voiding on the heat transfer characteristics at BTC component are not well understood. This paper will present some data to address these concerns.
Technical Library | 2014-10-30 01:48:43.0
The ultimate life of a microelectronics component is often limited by failure of a solder joint due to crack growth through the laminate under a contact pad (cratering), through the intermetallic bond to the pad, or through the solder itself. Whatever the failure mode proper assessments or even relative comparisons of life in service are not possible based on accelerated testing with fixed amplitudes, or random vibration testing, alone. Effects of thermal cycling enhanced precipitate coarsening on the deformation properties can be accounted for by microstructurally adaptive constitutive relations, but separate effects on the rate of recrystallization lead to a break-down in common damage accumulation laws such as Miner's rule. Isothermal cycling of individual solder joints revealed additional effects of amplitude variations on the deformation properties that cannot currently be accounted for directly. We propose a practical modification to Miner's rule for solder failure to circumvent this problem. Testing of individual solder pads, eliminating effects of the solder properties, still showed variations in cycling amplitude to systematically reduce subsequent acceleration factors for solder pad cratering. General trends, anticipated consequences and remaining research needs are discussed
Technical Library | 2009-05-07 23:23:00.0
Thermal fatigue has been one of the most serious problems for solder joint reliability. Thermo-mechanical fatigue failure is considered to be closely related to micro-structural coarsening (grain/phase growth). Factors that influence the phase growth are studied and measurement methods are discussed, including the preparation of the eutectic solder sample for phase size measurement. Three categories of models used to predict grain growth in polycrystalline materials are presented. Finally, phase growth in solder during high temperature aging and temperature cycling and its use as a damage correlation factor are discussed.
