FPC / PCB 工程計算機

PCB 線寬電流計算器：線寬與 IPC-2221 估算

依銅厚、溫升、內外層位置估算 PCB 線寬電流與目標電流所需線寬，適合 layout 前期檢查。

線寬電流計算器怎麼用

線寬電流計算用來在 layout 前期快速判斷 trace width 是否足夠。這個頁面把銅厚、溫升、內外層位置與目標電流放在同一個流程裡，先估算目前線寬可承載電流，再反推達到目標電流需要的線寬。FPC 因為材料薄、散熱條件和彎折區限制不同，結果應搭配實際 stack-up、溫升規格與工廠能力確認。

This PCB trace width current calculator helps engineers estimate whether a conductor width is reasonable before layout is frozen. It checks the current capacity of an existing trace and back-calculates the width required for a target current from copper thickness, temperature rise and layer position. The result is an early estimate and should be reviewed with stack-up, copper thickness and thermal conditions.

Legacy IPC-2221 style estimate

公式: I = k x deltaT^0.44 x A^0.725

  • I: estimated current in amperes.
  • k: empirical factor for external or internal layer.
  • deltaT: allowed temperature rise in degC.
  • A: conductor cross-sectional area in square mils, converted from trace width and finished copper thickness.
  • Required width: back-calculated from target current by solving the empirical equation for conductor area.

公式依據

  • Formula basis: legacy IPC-2221-style empirical conductor current equation.
  • Reference: IPC lists IPC-2221 as the Generic Standard on Printed Board Design and IPC-2152 as the current-carrying-capacity standard. https://www.ipc.org/ipc-design-standards
  • Engineering note: IPC-2152 and real thermal validation should be used for production current-carrying capacity decisions.

範例

例如 1 oz 外層銅、0.20 mm 線寬、允許 10 degC 溫升時，legacy IPC-2221 估算約可承載 0.74 A。若目標電流更高，工具會反推所需線寬，並提醒是否需要改銅厚、改 routing 或拆成多條電源路徑。

結果怎麼判讀

這個工具適合先做方向判斷，不適合當作唯一量產依據。若結果剛好貼近規格，應保留線寬、銅厚與散熱餘裕。

  • Estimated current capacity 大於目標電流，代表目前線寬在該溫升假設下有初步餘裕。
  • Required width 明顯大於目前線寬時，優先檢查是否能加寬、加厚銅、縮短路徑或改成多條並聯。
  • 外層線路通常比內層線路容易散熱，但仍會受 coverlay、焊綠、外殼、風流與鄰近熱源影響。

FPC 使用注意

FPC 的載流能力不只取決於線寬。彎折區、補強板邊緣、coverlay 開窗與連接器區都可能限制你能不能單純加寬線路。

  • 動態彎折區避免突然加寬或做銅面突變，否則可能造成應力集中。
  • 若電源線經過補強板邊緣，應同時檢查 stiffener setback 與彎折半徑。
  • 高電流 FPC 建議同時檢查壓降、功耗與局部溫升，而不是只看線寬電流。

什麼時候不能只看這個公式

  • 電流接近產品規格上限、外殼密閉、環境溫度高或 duty cycle 很高時，需要熱測或更完整模型。
  • 多層板、寬銅面、散熱銅箔、thermal via 與大面積 plane 會讓實際散熱和簡化公式不同。
  • 安全、車用、醫療或高可靠度產品，應依客戶規範、IPC-2152、工廠能力與實測結果做最後判定。

輸入欄位

  • Target current
  • Existing trace width
  • Finished copper thickness
  • Allowed temperature rise
  • Layer location
  • Internal / external conductor assumption

結果輸出

  • Estimated current capacity
  • Required width for target current
  • Cross-sectional conductor area
  • Pass / warning indication

工程注意事項

  • Use wider traces for long conductors, enclosed assemblies, hot environments or high duty cycle power paths.
  • FPC dynamic bend areas should not be widened by adding abrupt copper changes.
  • Use finished copper thickness, not only base copper weight, when plating changes the conductor cross-section.
  • Temperature rise is an engineering assumption. A 10 degC target is common for early review, but the correct value depends on the product.
  • For production release, compare the estimate with factory design rules and thermal validation.

驗證檢查

  • Conductor width DFM
  • Voltage drop
  • Copper thickness selection
  • Thermal risk
  • Bend-zone copper transition
  • Connector / stiffener area routing
  • Factory current-carrying design rule

相關製程站

  • 線路設計 - Trace width, spacing, bend-zone routing, differential pair spacing

相關計算器

FAQ

Can this replace thermal testing?

No. It is an early estimate. Real temperature rise depends on stack-up, air flow, enclosure, copper balance and load profile.

Why are internal traces lower capacity?

Internal conductors usually dissipate heat less efficiently than external conductors, so the empirical factor is more conservative.

How should I choose temperature rise?

Start with the product requirement or customer rule. If no rule exists, 10 degC is a common early-review assumption, but high-reliability or hot-enclosure products should use a stricter value and verify by test.

Can I use this for FPC power traces?

Yes, as an early estimate. For FPC, also review bend-zone routing, coverlay, stiffener edges, copper type, voltage drop and real assembly temperature.

Why does required width sometimes become very large?

The empirical equation is nonlinear. Higher current, lower temperature rise, thinner copper or internal-layer assumptions can quickly increase the required conductor width.