PCB / Reflow

Assembly · 14

Reflow

Paste melts and joints form. Profile, warpage and voids under the ESP32 pad show up here.

01 What happens

  • A thermal profile (preheat, soak, peak, cooling) is built for the paste and the heaviest package.
  • Lead-free peaks are typically in the 235–250 °C region; the ESP32 module vendor publishes a window.
  • Nitrogen is optional; it can help wetting on fine pitch, it does not fix a bad stencil.

02 On an ESP32 board

  • A large ESP32 module plus a small 0402 on the same board is a classic tombstone pair if paste and profile disagree.
  • QFN and module ground pads void if paste windows and peak time are wrong.
  • 0.8 mm boards warp; support the panel or the module corners lift.

03 What usually fails

  • Cold joints, charred parts, or connector melt from a copied ‘generic SAC305’ profile.
  • Colour change on the ESP32 shield can from over-peak.
  • Second reflow for bottom-side parts pushing the MSL budget.

04 What we check

  • We use the module vendor profile as the starting point, then add thermocouples on a first panel.
  • Double-sided SMT is planned, not discovered when the first side falls off.

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中文

PCB工艺 / 回流焊

组装 · 14

回流焊

锡膏熔化成焊点。温度曲线、翘曲、ESP32 大焊盘空洞，都在这里出现。

01 这一步做什么

  • 按锡膏和最重器件做预热、恒温、峰值、冷却。
  • 无铅峰值大致 235–250 °C；ESP32 模组厂有窗口。
  • 氮气可改善细间距浸润，救不了错误钢网。

02 落到 ESP32 板上

  • 大模组旁边小 0402，锡量和曲线不对就立碑。
  • QFN 和模组地垫窗口、峰值时间不对就空洞。
  • 0.8 mm 板会翘，拼板要托住，不然模组角会抬。

03 常见失败

  • 虚焊、器件烤黄、连接器熔化——套用「通用 SAC305」曲线。
  • 模组屏蔽罩变色，峰值过高。
  • 二次回流把潮敏预算用超，底面掉件。

04 我们查什么

  • 从模组厂曲线起步，首片贴热电偶。
  • 双面贴要事先排，不要第一面掉了才发现。

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