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Lead-free solders flow a little slower than 63/37 using the same activation levels for the fluxes.
The contact angles are slightly larger and feathering out of the solder is therefore less
pronounced. The solder joints tend to be less reflective than 63/37 solder. Some re-training is
required prior to a full transition to lead-free is done.
In some cases certain shrinkage effects as described in Section 5 of the IPC-STD-610D occur.
The IPC-610 classifies these as soldering anomalies and not necessarily defects.
As mentioned on page 5-22 of the above document, it is not a defect for Class 1, 2 and 3 if the
tear bottom is visible and the shrink hole does not contact the lead, land or barrel wall. See the
photos below for examples taken from the Kester laboratory.
What is the best soldering tip temperature for lead-free SAC and SnCu?
The temperature of the tip or contact temperature is very important to ease the lead-free handsoldering
operation. When using 63/37 solders temperatures as low as 650°:F have been used
but with lead-free 700-800°:F is best. The higher temperature does compensate for the slower
wetting exhibited with these lead-free alloys.
Above 800°:F issues of board and component damage may arise; at lower temperatures cold
solder joints and flagging are the normal complaints.
Higher temperatures and longer contacts with the parts to be soldered may also increase the
intermetallic bond layer. So avoiding prolonged contact and repeated rework is not
recommended. The above diagram shows what happens as the bond layer increases in
thickness a higher risk of embrittlement occurs.
The risk of de-wetting also increases with higher temperatures.
I think it will help you out.
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Hand assembly cosmetics
