If there is any certainty when doing PCB-RE, it is encountering 'unknowns'——components that are custom-built, without readily available information or datasheets. The proliferation of mobile devices and gadgets has seen ICs with multiple specialized functions integrated into a small wafer die,26 in a bid to reduce physical size and power consumption.
Take, for example, Apple's iPhone 5S motherboard shown below:
It's hard to imagine that so many components could be cramped within that 4.5-by-0.85 inch of physical space on both sides of the PCB, most of the chips being BGA-type and some with high pin-count footprints! This should come as no surprise, given that advances in wafer fabrication technology has already achieved under the sub 20-micron scale presently.
But don't be intimidated or become discouraged by this revelation. PCBs of this sort are an exception rather than the norm for manual PCB-RE. Truth is, it's not cost-effective to reverse engineer such boards in the first place, considering the low cost of manufacturing that arises from the high-volume production demands for these devices. It simply doesn't make economic sense.
That said, even in moderately complex through-hole or surface-mounted boards, do anticipate finding some unknown components as well. Sometimes it's not the big chips that stump you (though that is quite likely to happen) but the little discrete parts that seemingly look harmless enough until you try to identify them. Here's one example to prove my point: a reader once emailed me the following photos seeking my assistance to identify them:
Can you guess what these are? On first look, you may mistake them to be some sort of SMD resistors, except that the unique numbering and 3-terminal pinout provide tell-tale signs they are something else. Want to know what they are? Get a copy of PCB-RE: Real-World Examples and you'll learn their identity and many other useful tips.
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