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WLCSP Package Medical Care Monitor Medical PCB Assembly

MOKO Technology Ltd | Updated: Jul 11, 2017

                Portable health care equipment and services are becoming increasingly popular. In general, these devices must be efficient and ' invisible ', thus bringing new challenges to designers in terms of low power consumption and small volume. Today, wafer-level packaging (WLCSP) can make medical treatment impossible. The new applications include trauma testing, medical implants and disposable portable monitors. This article first introduces WLCSP technology, then discusses the PCB connection plate pattern, the welding disc finishes and the circuit board thickness design the best practical technique, in order to play the WLCSP maximum effect.Medical PCB Assembly

                 The finishing layer on the metal pad has a great influence on the assembly yield and reliability. A typical metal pad finishing agent uses an organic surface protector (OSP)/non-plated nickel immersion gold (enig). The thickness of the OSP treatment agent on the metal pad is 0.2μm to 0.5μm. This treatment will evaporate during reflow soldering and then interface between solder and metal pads. The Enig treatment agent consists of 5μm nickel plating and 0 02μm to 0.05μm Gold. During reflow, the gold layer dissolves quickly, followed by a reaction between the nickel and the solder. To prevent the formation of brittle metal interconnects, the thickness of the gold layer remains at 0.05μm the following is critical.Medical PCB Assembly

                 AD8235 installed in the center of the PCB. Circuit board stress (heat and mechanical stress) in the middle of the PCB minimum, the more to the edge of the PCB. Since the AD8235 is only 1.6mmx2.0mm, it bears less stress than a larger wlcsp. The use of 0.8mm ultra-thin PCB board can also reduce stress, because this PCB board more flexible, and in line with the thermal-mechanical stress sensing during the naked film characteristics. In addition, when the PCB bending, due to the AD8235 welding in a very small proportion of the surface area, and the rest of the PCB compared to the AD8235 area under the bending of the smallest changes. Because the width of the line is kept at two-thirds of the diameter of the opening window of the pad, the bending effect can be compensated further. Maintaining the ratio of two-thirds ensures that the solder bumps are not fully streamed to the wire, so that the encapsulation remains securely connected to the circuit board and has a reasonable upright height. The Enig solder disc finishes are selected here to be less than 0.05μm Gold layer to ensure reliable solder joints formation.Medical PCB Assembly

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