Powering-on your space electronics for the first time

文章：Rajan Bedi

无论是在您的实验室还是在FM硬件中进行测试的EM构建，在您的清洁室中进行验证，首次为您的空间电子设备供电总是令人生畏，但非常令人兴奋（非常令人兴奋（图1）对于最初的董事会“培养”，总有很多问题：您的设计功能是否功能？PCB是否可靠地制造？硬件是否正确组装了（例如，，，，是否将零件放置在正确的方向和/或检查BGA/CGAS以确保没有焊接桥）？一旦进入轨道，显而易见的是，航空电子学是否在发射的冲击和振动中幸存下来。

图1您真正收集了准备测试的空间级PCB。

以前，我出版了邮政关于设计空间电子设备和设计版制造（DFM）和设计构造（DFA）检查您需要执行的检查，以确保建造硬件是正确的。本月，我想第一次谈论在EM级原型上供电，以及在提供电压以及无创，故障发现的技术之前需要进行的检查，以防存在问题。

收到您的空间电子设备后，首次检查是视觉检查，以确保没有焊桥，锡晶石，墓碑，缺失的零件，缺少焊料，并且所有零件都已放置在正确的方向上，例如，半导体的引脚1作为阳性电容器或二极管等偏振组件。在发现制造商的包装图与其表壳标记之间的不匹配之后，我曾经有一个非常紧张的早晨，如图所示图2。这些检查中的许多需要数字显微镜和/或放大镜，因为我的视野不是曾经的。

图2包装销和标记之间的数据表不匹配。

Before powering up the assembled electronics, I always inspect a blank PCB for build quality and verify there are no short circuits between the power pads and GND. If there aren’t any, I then repeat the same continuity measurements on the un-powered, populated board to verify whether assembly has caused a short. This could happen for instance, with a solder bridge, a tin whisker, or a VCC pin inadvertently connected to GND (or vice versa) because the circuit symbol was incorrectly labelled, or the schematic was entered incorrectly. Generally, 90% of plane shorts are due to assembly errors! At this point I also check X-ray images of BGAs/CGAs to ensure these have been soldered properly (图3）。

图3An X-ray inspection of a space-grade memory chip.

Some semiconductors have parts underneath their lids and it’s always interesting to observe these on an X-ray—the first time I’d seen such an image, I didn’t understand the extra shapes as these components were not present on my PCB. As shown in图4，红色的零件位于FPGA外部，并放在板上，而绿色突出显示的零件则是设备的内部。

图4Parts under the lid of a space-grade BGA.

如果没有短裤，则可以施加功率。我通常从一个非常低的电压开始，该电压受到电流的限制，其较高的回旋速率在减慢到名义振幅之前。第一次检查是确保是否按预期绘制的电流，然后探测所需的功率导轨以确认已正确生成。在调节器旁边有测试点，无论是用于电压和返回的电压，以及用于EM构建的丝网印刷品，因此这些测量值变得更加容易，因为在将Gerber/ODB ++文件发送给制造商和给制造商和接收组装的硬件。如果电源轨道正确，我然后探测振荡器以检查时钟的存在和信号完整性。

如果有短裤,一个故障寻找th的过程enhas to take place to identify the cause of the short(s). Once of the first things I do is to take a thermal image using an infrared camera to identify where the shorts are. Hotspots in the thermal image will tell you which regulators are overheating (e.g., thermal cut-out) but will not reveal the origin or precise location of the short. During an initial power-on, I once discovered a POL enabled when it shouldn’t have been because the memory it was supplying had a plane short due to an error in design entry. The linear regulator at the bottom shown below was slightly warmer than normal as it was being asked to supply more current than its pre-set limit, triggering its internal thermal-protection circuitry (图5）。

图5A thermal image of the PCB after initial powering.

At the point when the hardware is powered off, I typically use a milli-ohm meter with Kelvin leads to check the resistance of all the passives attached to a shorted rail. Most conventional multi-meters do not have the required resolution and my experience has shown that most of the capacitors or resistors connected to the faulty supply have a similar value, e.g.，，，，15MΩ，如果其中之一是短的，则其电阻将低得多。这种方法已经确定了负责短路的故障组件。

If finding the short proves to be elusive, there are specialist tools available that inject an audio-frequency current onto the shorted rail as shown in图6。This tool follows the path of least resistance (or impedance), and then senses the current flow (EM field) using an inductive pick-up coil. The received signal is amplified and used to drive a speaker so you can hear the current path while moving the sensor around the surface of the PCB.

图6The inductive sensing of short-circuit current flow.

Two-dimensional vector plane stimulus can also be used to detect the location of a plane-to-ground short by injecting a current onto a plane (图7）。这会在PCB上产生潜在的梯度，并且测得的电压的极性可以引导您到达短路的位置，其中V1 + V2 = 0。

图7Two-dimensional vector plane stimulus to detect plane to ground short.

Other instruments measure milli-ohm resistance with the pitch of the sound increasing as you approach the offending short-circuit—this is useful for locating a short between traces!

Space-grade (and also some COTS) parts can be very expensive, and I always start by using non-invasive, fault-finding techniques to locate a problem before getting the soldering irons out to surgically remove a component—I’ve never been a fan of randomly lifting parts to identify the defective one as this is too time consuming and too destructive!

如果您想第一次了解有关DFM，DFA和PCB供电的更多信息，teaches课程Right-First-Time, Space-Grade PCB Design, Layout, Manufacture, Assembly and Test.SpaceChips的测试部门还提供PCB调试服务，因此，如果您希望我们检查和提出您的董事会，请与我联系。

直到下个月，第一个告诉我为什么在测量小电阻时不太准确的传统，两个铅的多米都不会赢得Courses for Rocket ScientistsWorld Tour tee-shirt. Congratulations to Faheem from Malaysia, the first to answer the riddle from my previous post.

本文最初发表在EDN。

Rajan Bedi博士是首席执行官和创始人Spacechips，，，，which designs and builds a range of advanced, L- to Ku-band, ultra-high-throughput transponders, on-board processors and edge-based OBCs for telecommunication, earth-observation, navigation, internet and M2M/IoT satellites. The company also offers Space-Electronics Design-Consultancy, Technical-Marketing, Business-Intelligence, Avionics Testing and Training Services. You can also contact Rajan onLinkedInand推特。

Spacechips’ Design-Consultancy Services develop bespoke satellite and spacecraft sub-systems, as well as advising customers how to use and select the right components, how to design, test, assemble and manufacture space electronics.