Seasons Greetings!

Christmas is just round the corner following the winter solstice. It's the time of the year to gather with people you love and care about, to spend quality time and enjoy their company over heart-warming meals and moments.

It's also a time to reflect and reminiscent, and then look forward to a new year, hopeful of a better and brighter future. And while we're at it, let's not forget to go something good to help the less fortunate, be it charity or community volunteering work. For readers who have bought my books, I would like to thank you for your honest purchase, and to let you know that part of the royalties goes to support the National Kidney Foundation (NKF), so you're actually contributing to charity as well.

Here's wishing all my readers:

Stay safe and well through the season holidays!

Packaging Challenges

You might be surprised to know that electronics packaging predates the printed circuit board. Over the past 60 years, packages have continued to shrink in footprints yet increase in functionalities. Some packages are no bigger than the period at the end of this sentence.Today, there are more types of packages than ever before that can be found mounted on a given PCB. The ever expanding package acroniums is proof of this phenomenon: QFN, QFP, SOT, TSSOP, PDIP, WLCSP, BGA, FPBGA, SOIC, PoP, COF, WLP, FOWLP, and many more.

COF and WLP Packaging

This increasing trend in PCB design also presents challenges to PCB reverse engineering, especially for newbies and occasional apprentices. Identifying these components is one thing; finding related information and datasheets is another; yet still to overcome is the accessibility of probe points since most of these use BGA footprints with high-density pin-counts to reduce PCB real estate. It's a literal nightmare for manual PCB-RE work.

So unless you have the resources to do it, my advice is to steer clear of them unless it's a do-or-die mission. Remember, you have been warned.

Deciphering Components

Except for ICs and components with large surface areas which permit printing of part numbers most surface mount devices use some form of cryptic coding system to indicate their identities or values. Some basic components like resistors, resistor networks, and capacitors may also contain long strings of alphanumeric characters that require their manufacturers' references to make sense of their package and content. Take for example the two types of through-hole resistor coding:

The pair on the left uses color coding, with four and five bands of color for the top and bottom resistors, respectively. The pair on the right shows the same value in alphanumeric notation wrapped around the resistor's body. Resistor color and numerical codes are necessary for deciphering both color and alphanumeric codes found on resistors and capacitors.

Surface-mounted devices, passive and active, are becoming common place these days so it's good to keep a copy of SMD codebook at hand for easy reference and be familiar with their outlines and packaging.

Exercise: Can you identify and decipher the components on a PCB shown below?

According to their layout:

Chip Capacitor, Tantalum                                                  Chip Resistor, size 0603

1uF 35V                                                                             10 Ohms

Diode, case SOD-80               Low-Capacitance               NPN Transistor, SOT-323

Switching                                Diode Array (5V)                 BFR92AW

Chip Resistor, size 0805

4.64K                                                                                 Chip Capacitor, unknown

Chip Capacitor, unknown

How many did you manage to get right?

Ps: If you have purchased The Art of PCB Reverse Engineering, you are entitled to get a copy of the SMD Code Reference Book (500+ pages) and other goodies.

An Identity Crisis

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.