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參數資料
| 型號： | AN-994-1 |
| 廠商： | International Rectifier |
| 英文描述： | MAXIMIZING THE EFFECTIVENESS OF YOUR SMD ASSEMBLIES |
| 中文描述： | 最大限度地發(fā)揮你的貼片組件效果 |
| 文件頁數： | 6/7頁 |
| 文件大?。?/td> | 120K |
| 代理商： | AN-994-1 |
Section V: Heat profiles
Reflow Soldering Heat Profiles
A major problem associated with surface mounting of
electronic components, especially those with
mismatched internal expansion coefficients is the
thermal shock of the soldering process. The advent of
lead free assemblies has driven the requirement to
develop and implement new handling techniques for
surface mounting devices. Typical lead free solders
have higher melting point temperatures than the
traditional Pb based solders. Whereas previously,
assemblies could be mounted at peak reflow
temperatures in the range of 220
°
C to 245
°
C, Pb free
assemblies require reflow temperatures in the range of
245
°
C to 260
°
C. The higher peak reflow temperatures
require careful control of the reflow environment to
prevent over temperature conditions that can severely
degrade the reliability of surface mount devices.
Caution must be taken when choosing the reflow
profile in order to optimize the thermal stresses that are
applied to either Pb based or Pb free assemblies.
6 of 7
In addition to the over temperature considerations,
under temperature conditions can in turn result in a
failure of the mechanical attachment of the device
during the reflow profile. A carefully controlled preheat
and post-cooling sequence is necessary. Properly
controlling the preheat cycle will remove any volatile
component of the solder paste such as alcohol or
water by evaporation prior to the solder fusing cycle.
This will reduce the chances of forming void or solder
ball.
This thermal conditioning can be applied in several
ways such as using Infrared/Convection ovens, Vapor
Phase, or Wave Solder equipments. The
recommended thermal conditioning method is the
Infrared/Convection Soldering Temp / Time Profile
described below:
Infrared/Convection Soldering Temp/Time Profile.
The critical parameters shown below are defined in
table 2 by solder paste type and device volume.
TSmax
TSmin
t
p
TL
TP
ts preheat
t
L
Ramp down
Ramp up
t
25
°
C to peak
Time
Temperature
Figure 5:
Soldering & Test Profile
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