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Joined: 12 Jun 2026
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 Posted: Sun Jun 22, 2026 11:07 pm Post subject: |
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Reposted from SFE's old Assembly Forum
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Date: 26 Apr 2026
Time: 02:54:57
Remote Name: 137.71.23.54
Remote User:
Hello Popcorn Crazy,
Welcome to the assembly forum!
Popcorn cracking simply refers to package cracking of a surface mount device caused by excessive moisture ingress into the package and extremely high board soldering peak temperature. All packages absorb moisture from the air around it, with the absorption rate depending on a multitude of factors: package characteristics, relative humidity, ambient temperature, etc. It turns out that some packages, especially the thinner ones, are more prone to absorb moisture from its surroundings than others.
Excessive moisture inside a package won't be a problem until the package undergoes board soldering. During board soldering (usually by IR reflow), the high temperature vaporizes the moisture inside the package. The violence with which the trapped vapor will try to escape from the package will result in internal thermomechanical stresses that are strong enough to delaminate the package.
Package delamination is the only way these internal stresses may be relieved, so delam is almost always expected in moisture-sensitive units after board-mounting. The delam occurs at the die paddle-mold interface, and may cover the entire die paddle in extreme cases.
Some packages are structurally weak that this delamination extends into package cracking before the internal stresses are relieved. This cracking mechanism is so fast, that it even becomes audible, which is why this has been known as 'popcorn cracking.' The cracking originates from the corners of the die paddle and propagates downward at a 45-degree angle.
Prevention of excessive moisture absorption prior to board-mounting is necessary to preclude packages from exhibiting popcorn cracking. Moisture-sensitive devices must undergo bake and dry-packing prior to shipment to customers, and must be board-mounted by manufacturers within a prescribed number of hours once taken out of the bag. Thus, the moisture sensitivity level of any new package must be determined prior to mass-production and shipment to customers.
More power to you!
EE
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