Page 7.7
7.0 Soldering profile management and production
Profile management 551.19 \ 12.2015 \
a higher temperature level and so decrease the stress for all com-
ponents.
Maximum temperature
The maximum temperature T
p
of a reflow profile is also called peak
temperature. Higher temperatures decrease the surface tension
of the liquid solder and enhance the flow behaviour. Experiences
in the praxis have shown, that an overheating of 5-10% above the
melting point is advantageously. For SnAgCu with T
L
= 217 °C and
an overheating of 5% a T
p
= 241,5 °C is advisable.
The limitative factors for the max. temperature are the max. al-
lowed stress temperatures and times for the components and the
PCB. The JEDEC IPC 20B [5] recommends a max. temperature
of 250°C (10 - 30s) for the lead free process, for which the com-
ponents should be qualified. To decrease the potential for possible
damages, lower temperature levels are advantageously. Neverthe-
less it is necessary to secure that the solder paste was completely
remelted and a good wetting of the join partners was achieved.
For this always the temperature at the "coldest" solder joint must
be observed.
Heating-up and cooling down gradient
The temperature gradients dT/dt should be small in each phase of
the soldering profile (especially for the preheating),
e,g. dT/dt < 3 K/s. On one hand the thermal stress for the com-
plete assembly (components and PCB) will be limited by this way,
and on the other hand errors, caused by steep gradients will be
avoided.
These errors are:
Solder balling - caused by the explosively evaporation of solvents
in the solder paste and the resulting skidding of paste grains out of
the solder paste.
Tombstoning - because of different melting times of the both solder
depots at two pole components, the wetting force of the already
liquid solder causes an erecting of the component.
Wicking effect - because of a too quick heat input in the compo-
nent contact, the solder of the joint will be pulled away from the
solder pad and flows upwards to the component contact.
Popcorn effect - because of a too quick heat input in the compo-
nent it is possible that enclosed humidity (caused by improper
Ramp-up / Ramp-
down gradient
Peaktemperature
Summary of Contents for 551.10
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Page 100: ...Page 6 26 6 0 Function and start up Function 551 19 12 2015 Menu structure Setup ...
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Page 134: ...8 0 System settings Page 8 2 System_settings 551 19 12 2015 ...
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Page 220: ...11 0 Options and spare parts Optionen 551_19 12 2017 Page 11 12 Server software setup ...
Page 222: ...11 0 Options and spare parts Optionen 551_19 12 2017 Page 11 14 Create user ...
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Page 226: ...11 0 Options and spare parts Optionen 551_19 12 2017 Page 11 18 Set up external operation ...
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