Graping is a phenomenon which appears as un-reflowed solder particles, typically seen on the surface of the solder joint.
The graping phenomena has become more common due to some of the following issues:
- Reduction of the stencil aperture to accommodate smaller and smaller discrete and passive components (i.e. move from 0603”s to 0402”s to 0201’s)
- 使用粒度更细的焊膏，以适应精细特征印刷（从 3 型到 4 型，再到现在的 5 型）
- 用于无铅 焊接的更高回流焊特性
- The use of water-soluble vs. no-clean solder pastes. No-clean chemistries generally protect the solder powder particles and the metallized surfaces from oxidation during the heating process (after the activator package removes existing oxides). (so how does water-soluble fit into this?)
这些因素的组合可能会耗尽焊膏助焊剂去除表面氧化物的能力。这会耗尽助焊剂，使焊膏颗粒氧化，这意味着焊料颗粒无法凝聚成焊点。
To avoid the graping phenomenon, use the following tips in setting up your reflow profile. The intent here is to decrease the amount of heat the solder paste experiences during the reflow process.
- A ramp to peak profile is better than a soak profile
- 通过调整传送带速度来缩短烤箱内的总时间。建议从环境温度到峰值的升温速度为每秒 1°C
- Use a lower peak temperature – 235°-240°C
- 将 TAL 缩短至 40-60 秒
For more information please refer to "Best Practices Reflow Profiling for Lead-free SMT Assembly"
