Pushing the Limits of Packaging

　　Pushing the Limits of Packaging

　　微控制器的封装在系统的小型化中起着关键作用。对外围设备的选择上的权衡，垫计数和芯片尺寸都限制了能力，以减少微控制器的大小，但仍有助于减少终端设备的整体尺寸。

　　热的问题也很重要，考虑到微控制器得到更小的尺寸。在较小的芯片上有更多的晶体管，在更高的频率运行，功耗是一个关键的考虑因素。同时降低电压和门控不同的外设，使未使用的元素不消耗功率，可以减少整体的热负荷，多余的热量产生，然后必须有效地删除或微控制器将降级，最终失败。这是一个关键的可靠性问题，必须考虑小型单片机系统。

　　这是引脚与大小的权衡进来。在封装上的附加引脚可用于连接到热过孔，从微控制器和其他设备，可能是敏感的温度升高，如无线接口带走多余的热量。

　　While the latest chip-scale packaging can reduce the overall footprint of a device with a given functionality， reducing the area taken up by a quarter， the opportunity to integrate more peripherals into a device and have more pins for thermal dissipation may be more important.

　　The designer also has to be aware of the aim of miniaturization. An ARM 32-bit core， such as the Cortex-M0+ or even the M4， is less than a square millimeter of silicon – the size of the die is determined more by the amount of memory on chip and， vital for the packaging consideration， the peripherals that need to connect to the outside world. The smallest M0 devices， such as Freescale’s Kinetis KL02， can be as small as 1.9 x 2.0 mm in a chip-scale package that is barely larger than the die itself. At less than 4 square millimeters， this occupies twenty-five percent less PCB area than ball grid array or LGA packages but provides sixty percent more GPIO with up to twenty-eight lines. This move， almost ‘silicon dust’， allows designers to dramatically reduce their board size without compromising the performance， feature integration and power consumption of the end products.