AMD does not support soldering SnAgCu BGA connectors with Sn/Pb solder paste during the soldering process. Traditional Sn/Pb soldering processes have a peak reflow temperature of 220°C. At this temperature range, the SnAgCu BGA solder balls cannot properly melt and wet to the soldering surfaces. As a result, reliability and assembly yields can be compromised.
The optimal profile must take a few factors into account:
- Solder paste flux used
- Size of the board
- Density of the components on the board
- Ratio of large and small, lighter components (the mixture)
Profiles should be established for all new board designs using thermocouples placed at multiple locations on the component. In addition, if there is a mixture of devices on the board, the profile should be checked at various board locations to ensure that the minimum reflow temperature is reached on the larger components, and at the same time the temperature does not exceed the threshold that might damage the smaller, heat sensitive components.
The following tables and figures provide the recommended guidelines for Pb-free solder PCB assembly reflow. In general, a gradual-linear ramp into a spike is proven, by various sources, to be the optimal reflow profile for Pb-free solder. This profile results in a better wetting yield and less thermal shock than the conventional ramp-soak-spike profile. It is a known fact that SnAgCu (SAC) alloy reaches its full liquidus at a temperature of 235°C. In the reflow profiling, the coldest solder joints need to be identified and to ensure that they reach a minimum peak temperature of 235°C for at least 10 seconds. Reflowing at high-peak temperatures of 260°C or above can damage the heat sensitive components and cause board warpage. Refer to the latest IPC/JEDEC J-STD-020 standard for allowable peak temperature on the components. The allowable component peak temperature is determined by the component size. The following table lists the reflow soldering temperature profile information. In any case, use as low of a peak temperature reflow profile as possible. The following image shows an example of the reflow temperature profile.
| Profile Feature | Convection, IR/Convection |
|---|---|
| Preheat ramp-up rate 30°–150°C | 3°C/s maximum |
| Preheat temperature soak time 150°–200°C | 60–120 seconds |
| Temperature maintained above 217°C | 60–120 seconds (60–90 seconds typical) |
| Time within 5°C of actual peak temperature | 30 seconds maximum |
| Peak temperature (lead/ball) | 235°C–245°C typical (depends on solder paste, board size, component mixture) |
| Ramp-down rate | 4°C/s maximum |
