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Smartphones are complex, costly devices and therefore need to be reworked correctly the first time.
To meet the ever-growing demand for performance, the complexity of mobile devices has increased immensely, with 70% more packages now found inside a mobile device than just a few years ago. For instance, a 1080P HD camera with video capabilities is now available on most high-end smartphones or tablet computers, making their production more elaborate and expensive.
The printed circuit boards for these devices are no longer considered disposable goods, and their bill of materials start from $150, with higher-end smartphones going up to $238, and tablets well over $300.
The implementation of surface mount devices is crucial for smartphone manufacturers, offering increased component density and improved performance. For example, the newer style DDR memory integrated components use less power and work at twice the speed of former versions. It is not surprising that most component manufacturers now produce these surface mount devices as small as 1 mm square.
Mobile products generally use an epoxy underfill to adhere components to the printed circuit board to meet the mechanical strength requirements of a drop test. Reworking glued components is the most difficult application in the electronics industry, and must be addressed as a process.
Rework Challenges
The removal of a glued component from a PCB assembly requires a specific order of operations. The first step is to remove the glue fillet located between the component and the circuit board. Mobile products generally have many types of components glued to the PCB in order to meet the industry standards outlined in JESD22-B111 Board Level Drop Test Method of Components for Handheld Electronic Devices and JESD22-B110 Subassembly Mechanical Shock. The epoxy is applied to the components to prevent the common failure modes of cracks in the laminate, cracks near the intermetallic, and cracks in the bulk solder. The addition of the epoxy increases the robustness of the design and enhances reliability for the user.
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Editor's Note: This article originally appeared in the November 2014 issue of SMT Magazine.
