Figure 20 - uploaded by Nakul Kothari
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-Cross-section of good solder joint shows cross-section of solder joint in QFN package. Average height of solder was found to be 70µm and was consistent throughout the package. Average width of the solder interface was around 230µm -250µm and the length was around 360µm-390µm. After reflowing, thin layer of IMC was observed at the PCB (HASL finish) and package side (Matt tin finish) which indicates good bonding between solder paste and pad. Cycles to failure were tracked for all packages and Weibull plot was created using WinSMITH software. Weibull distribution is shown in Figure 21. The -value, or the characteristic life representing 63.2 percent of failures was found to be 1324 cycles. Beta value of the distribution was 23.12. Red dashed lined represents x and y coordinates of the characteristic life data point.
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... In addition to the technological challenges, the focus is already on size and cost reduction. While Ball Grid Array (BGA) packages are often very expensive and not suitable for small I/O count applications, Quad Flat No Leads (QFN) packages are a smaller and cheaper alternative with better thermal performance [1]. QFN packages are characterized by an overmolded lead frame on the bottom and a thermal pad in the center. ...
... Many studies have already shown a high impact of surface strain and temperature on the solder fatigue life on surface mounted devices (SMD) such as QFN components. Regardless of whether it is harmonic vibration [2], mechanical shock [3], thermal cycling [1], thermal shock [4] or even a combination of loads [5], increasing loads result in a reduced solder fatigue life. ...
... This procedure is explained in the Sections 2.4 and 2.5. Useful tips and relevant information about board-level reliability of different components (without 2nd level encapsulation) are available in different sources [11][12][13][14][15][16][17][18][19]. These sources lay out the best practices used for defining and testing board-level reliability, involving the reliability analysis of commonly used components like ball grid arrays (BGAs) [13,16], quad-flat no-leads packages (QFN) [11,15], and thin small outline packages [17]. ...
... Useful tips and relevant information about board-level reliability of different components (without 2nd level encapsulation) are available in different sources [11][12][13][14][15][16][17][18][19]. These sources lay out the best practices used for defining and testing board-level reliability, involving the reliability analysis of commonly used components like ball grid arrays (BGAs) [13,16], quad-flat no-leads packages (QFN) [11,15], and thin small outline packages [17]. The effect of 2nd level encapsulation, e.g., by means of conformal potting on QFN reliability is presented in [20]. ...
A drastically growing requirement of electronic packages with an increasing level of complexity poses newer challenges for the competitive manufacturing industry. Coupled with harsher operating conditions, these challenges affirm the need for encapsulated board-level (2nd level) packages. To reduce thermo-mechanical loads induced on the electronic components during operating cycles, a conformal type of encapsulation is gaining preference over conventional glob-tops or resin casting types. The availability of technology, the ease of automation, and the uncomplicated storage of raw material intensifies the implementation of thermoset injection molding for the encapsulation process of board-level packages. Reliability case studies of such encapsulated electronic components as a part of board-level packages become, thereupon, necessary. This paper presents the reliability study of exemplary electronic components, surface-mounted on printed circuit boards (PCBs), encapsulated by the means of thermoset injection molding, and subjected to cyclic thermal loading. The characteristic lifetime of the electronic components is statistically calculated after assessing the probability plots and presented consequently. A few points of conclusion are summarized, and the future scope is discussed at the end.
... X-ray slice with void X-ray slice with void after Otsu Image Segmentation χ χ This type of diffusion smoothing does not affect the existing mesh connectivity. The discrete approximations of the Laplacian Operator take the general form, (18) Calculation of the weights can be done by using simple approximation, scale-dependent Laplacian, and curvature normal approximation. ...
Lead-frames have been widely used in the semiconductor package assembly field, and QFN (Quad flat no leads) has the advantages of miniaturization and cost reduction of the semiconductor package. It has had limited use in automotive or defense products because of its board-level reliability. Nevertheless, due to the advantages of QFN packages, there is a trend toward using QFNs in automotive packaging. Automotive use would also require a wettable flank design of the QFN leads and automated optical inspection (AOI) of solder joints. New lead forming and surface finish technologies, including wettable flank design, are expected to improve reliability and enable AOI inspection, but much research is needed. This study investigated the board-level reliability of various QFN lead designs and surface finishes. All lead frames with different structures and surface finish types were assembled under the same conditions and then mounted on a daisy chain printed circuit board to evaluate board-level reliability. Accelerated thermal cycling (TC) tests were performed per IPC-9701A rev 2/2006 over a temperature range of -40°C to 125°C and 6080cycles. Lastly, each package type tested was cross-sectioned, and failure analysis was performed by observing the solder joint crack for all leg samples.
