PCA88021 NXP [NXP Semiconductors], PCA88021 Datasheet - Page 30

• Manufacturer Part Number: PCA88021
• Description: ultra low power oscillator with integrated counter for initiating one time password generation
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCA8802_1
Product data sheet
16.3.1 Stand off
16.3.2 Quality of solder joint
16.3.3 Rework
For further information on temperature profiles, refer to application note AN10365
“Surface mount reflow soldering description” .
The stand off between the substrate and the chip is determined by:
The higher the stand off, the better the stresses are released due to TEC (Thermal
Expansion Coefficient) differences between substrate and chip.
A flip-chip joint is considered to be a good joint when the entire solder land has been
wetted by the solder from the bump. The surface of the joint should be smooth and the
shape symmetrical. The soldered joints on a chip should be uniform. Voids in the bumps
after reflow can occur during the reflow process in bumps with high ratio of bump diameter
to bump height, i.e. low bumps with large diameter. No failures have been found to be
related to these voids. Solder joint inspection after reflow can be done with X-ray to
monitor defects such as bridging, open circuits and voids.
In general, rework is not recommended. By rework we mean the process of removing the
chip from the substrate and replacing it with a new chip. If a chip is removed from the
substrate, most solder balls of the chip will be damaged. In that case it is recommended
not to re-use the chip again.
Fig 36. Temperature profiles for large and small components
•
•
•
The amount of printed solder on the substrate
The size of the solder land on the substrate
The bump height on the chip
temperature
MSL: Moisture Sensitivity Level
Rev. 01 — 19 February 2009
= minimum soldering temperature
maximum peak temperature
minimum peak temperature
= MSL limit, damage level
temperature
peak
PCA8802
© NXP B.V. 2009. All rights reserved.
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