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--- decap:explosive [2013/12/28 01:00] – created azonenberg
+++ decap:explosive [2014/08/18 07:05] (current) – azonenberg
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 "Explosive decap" is a tongue-in-cheek term referring to blowing a semiconductor device to bits (usually by accident). While this is rarely intentional, the remaining fragments can be interesting to study.
-The primary mechanism of explosive decap is the same as "popcorning" in BGAs: trapped water vapor in the packaging boils, has nowhere to escape, and ruptures the packaging with a small steam explosion. There is, however, one key difference: popcorning is induced by the soldering process (and typically is less dramatic in appearance due to the slower thermal gradients). Explosive decap, however, is much more rapid: common malfunctions such as short circuits or connecting power backwards will heat the device from room temperature to >Tjmax in a fraction of a second, causing much more vigorous fragmentation.
+====== Mechanism of operation ======
-Small pieces of chip shrapnel may be thrown several feet in extreme cases. The example described below involved connecting a 7805 linear regulator to a miswired (unprotected and polarity reversed) 11.2V Li-ion battery pack. The extremely low ESR battery voltage being dumped into what was effectively a forward-biased zener diode caused a massive thermal spike which blew the front half of the TO-220 across the room and exposed most of the die.
+The primary mechanism of explosive decap is the same as "[[http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=367494&tag=1|popcorning]]" in BGAs: trapped water vapor in the packaging boils, has nowhere to escape, and ruptures the packaging with a small steam explosion. There is, however, one key difference: popcorning is induced by the soldering process (and typically is less dramatic in appearance due to the slower thermal gradients). Explosive decap, however, is much more rapid: common malfunctions such as short circuits or connecting power backwards will heat the device from room temperature to >Tjmax in a fraction of a second, causing much more vigorous fragmentation.
+Small pieces of chip shrapnel may be thrown several feet in extreme cases.
+Explosive-decapped PIC18F4550 showing most of the die exposed (courtesy of Viper-7):
+{{:decap:exploded_pic.jpg?700|}}
+====== Example (7805 regulator) ======
+This case involved connecting a TO-220 packaged 7805 linear regulator to a miswired (unprotected and polarity reversed) 11.2V Li-ion battery pack. The extremely low ESR battery voltage being dumped into what was effectively a forward-biased zener diode caused a massive thermal spike which blew the front half of the TO-220 across the room and exposed most of the die. A yellowish flash of light was visible as well, which may have been an incandescent fragment of bond wire or burning package fragment.
+The remainder of the device after explosive decap with partially exposed die and leadframe. The rounded crater at upper right is most likely the location of of the original explosion.
+{{:decap:blown_7805_big.jpg?600|}}
+Recovered package fragment. Note shell over leadframe at right side and blast crater just to the left.
+{{:decap:7805_shrapnel.jpg?600|}}