AN10365_3
© NXP B.V. 2008. All rights reserved.
Application note
Rev. 03 — 22 April 2008
8 of 24
NXP Semiconductors
AN10365
Surface mount reflow soldering description
Leaded packages (e.g. SO and QFP)
•
With leaded packages, coplanarity is an important issue; coplanarity must be within
the specifications (refer to the package outline drawing) in order to prevent the
occurrence of open circuits or bad joints; poor coplanarity may also increase
problems caused by board warpage
•
The tips of leads, where they are cut out of the lead frame, do not have to be wetted
after reflow
•
Within NXP, two possible lead finishes are applied: pure Sn and NiPdAu; the finish
used depends on the package family. SnPb finish is still used, but only for selected
applications
•
Leaded packages are reflow solderable; standard gull wing packages are wave
solderable only if the lead pitch is equal to, or larger than 0.65 mm and no exposed
heatsink is present; wave soldering smaller pitches will lead to a higher defect level
Leadless packages with solder balls (e.g. BGA and TFBGA)
•
These IC packages are particularly good at self-alignment, as the package body is
essentially suspended over molten solder during reflow; therefore, this package type
results in a robust reflow soldering process
•
The balls are made of SnPb, or SAC for Pb-free applications
•
Packages with solder balls are only reflow solderable, they cannot be wave soldered
Fig 6.
Package types
Fig 7.
Example of a QFP
001aac834
leads
solder balls
terminal types
lands (leadless)
001aac835
