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AX5243 Datasheet(PDF) 41 Page - ON Semiconductor |
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AX5243 Datasheet(HTML) 41 Page - ON Semiconductor |
41 / 42 page AX5243 www.onsemi.com 41 QFN20 Recommended Pad Layout 1. PCB land and solder masking recommendations are shown in Figure 16. Figure 16. PCB Land and Solder Mask Recommendations A = Clearance from PCB thermal pad to solder mask opening, 0.0635 mm minimum B = Clearance from edge of PCB thermal pad to PCB land, 0.2 mm minimum C = Clearance from PCB land edge to solder mask opening to be as tight as possible to ensure that some solder mask remains between PCB pads. D = PCB land length = QFN solder pad length + 0.1 mm E = PCB land width = QFN solder pad width + 0.1 mm 2. Thermal vias should be used on the PCB thermal pad (middle ground pad) to improve thermal conductivity from the device to a copper ground plane area on the reverse side of the printed circuit board. The number of vias depends on the package thermal requirements, as determined by thermal simulation or actual testing. 3. Increasing the number of vias through the printed circuit board will improve the thermal conductivity to the reverse side ground plane and external heat sink. In general, adding more metal through the PC board under the IC will improve operational heat transfer, but will require careful attention to uniform heating of the board during assembly. Assembly Process Stencil Design & Solder Paste Application 1. Stainless steel stencils are recommended for solder paste application. 2. A stencil thickness of 0.125 – 0.150 mm (5 – 6 mils) is recommended for screening. 3. For the PCB thermal pad, solder paste should be printed on the PCB by designing a stencil with an array of smaller openings that sum to 50% of the QFN exposed pad area. Solder paste should be applied through an array of squares (or circles) as shown in Figure 17. 4. The aperture opening for the signal pads should be between 50−80% of the QFN pad area as shown in Figure 18. 5. Optionally, for better solder paste release, the aperture walls should be trapezoidal and the corners rounded. 6. The fine pitch of the IC leads requires accurate alignment of the stencil and the printed circuit board. The stencil and printed circuit assembly should be aligned to within + 1 mil prior to application of the solder paste. 7. No−clean flux is recommended since flux from underneath the thermal pad will be difficult to clean if water−soluble flux is used. Figure 17. Solder Paste Application on Exposed Pad |
Similar Part No. - AX5243_16 |
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Similar Description - AX5243_16 |
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