SMT Electronics Assembly, SAC305 Lead-Free Reflow Profiling & IPC/JEDEC J-STD-020
SMT Reflow Oven Belt Speed, Ramp Slope & TAL Formula
Calculate Preheat Zone Residence Time (s), Preheat Thermal Ramp Slope (°C/s <= 3.0 °C/s limit), Peak Zone Time Above 217 °C SAC305 Liquidus TAL (s), and J-STD-020 Profile Audit.
Cranking reflow conveyor speed up to chase SMT line beat rate slashes TAL below 45 seconds—causing cold head-in-pillow BGA joints AND thermal-shock tombstoning!
In a multi-zone forced-convection SMT reflow tunnel running at Mesh/Pin Conveyor Speed `v_belt` (cm/min -> `v_belt / 60` cm/s), every PCB thermocouple profile balances TWO opposing IPC/JEDEC J-STD-020 limits for lead-free `SAC305` (`Sn96.5Ag3.0Cu0.5`, melting liquidus `217 °C`): (1) **Preheat Ramp Slope** `Slope = (T_soak - T_amb) / (L_preheat / (v_belt / 60))` MUST stay `<= 3.0 °C/s` (`1.5–2.5 °C/s` ideal) so ceramic MLCC capacitors do not crack and volatile flux solvents do not boil explosively ("solder balling" / `0402` tombstoning!), and (2) **Time Above Liquidus (`TAL`)** `t_TAL = L_above_217 / (v_belt / 60)` MUST land inside **`45` to `90` seconds** (`< 45` s fails to wet CuOSP/ENIG pads into a sound `Cu6Sn5` intermetallic layer; `> 90` s grows thick brittle intermetallic and delaminates IC packages)!
Verify on a 10-Zone Lead-Free SAC305 Convection Oven—Conveyor_Speed `v_belt` = 80.0 cm/min (`1.333` cm/s, B2), Preheat_Ramp_Length `L_pre` = 96.0 cm (B3 -> Preheat Dwell = `72.00` s in E2), Room_Entry_Temp `T_amb` = 25.0 °C (B4), Flux_Soak_Entry_Temp `T_soak` = 155.0 °C (B5 -> Ramp Slope = `1.81 °C/s <= 3.0 °C/s` in E3), and Effective_Tunnel_Length_Above_217C `L_TAL` = 84.0 cm (B6): Time Above Liquidus equals `63.00` s (E4), passing `"J-STD-020 SAC305 PASS"` (E5)!
| IPC/JEDEC J-STD-020 Reflow KPI (Belt=80 cm/min, L_pre=96 cm, L_TAL=84 cm) | Formula | Verified Output |
|---|---|---|
| Preheat Zone Residence (sec) | Preheat_Len_cm / (Belt_cm_min / 60) | 72.00 s (46.08 s @ 125 cm/min rush) |
| Preheat Ramp Slope (°C/s) | (T_soak_C - T_amb_C) / Preheat_Time_s | 1.81 °C/s (2.82 °C/s @ 125 cm/min) |
| Time Above 217°C Liquidus TAL (s) | Peak_217_Len_cm / (Belt_cm_min / 60) | 63.00 s (40.32 s < 45s @ 125 cm/min!) |
| J-STD-020 SAC305 Window Gate | Slope <= 3.0 AND 45 <= TAL <= 90 | J-STD-020 SAC305 PASS |
Conveyor Residence Time, Thermal Ramp Slope & SAC305 TAL Window Formula
Validate `Belt_Speed` in `(10, 300]` cm/min, `Preheat_Len > 0` cm, `0 <= T_amb < T_soak <= 217` °C, and `Peak_Above_217_Len > 0` cm right on `E2` (checking `ISTEXT(E2)` on `E3..E4` so text status strings in `E5` never block numeric cells)!
=LET(vb_m, B2, lp_c, B3, ta_c, B4, ts_c, B5, lt_c, B6, IF(OR(vb_m <= 10, vb_m > 300, lp_c <= 0, ta_c < 0, ts_c <= ta_c, ts_c > 217, lt_c <= 0), "Invalid Reflow Input", LET(vc_s, vb_m / 60, tp_s, lp_c / vc_s, sl_p, (ts_c - ta_c) / tp_s, tl_s, lt_c / vc_s, IF(AND(sl_p <= 3, tl_s >= 45, tl_s <= 90), "J-STD-020 SAC305 PASS", "OUT OF REFLOW WINDOW"))))Over-Sped 125 cm/min Conveyor Cold-Solder Wetting Failure Check (Set Belt Speed B2 = 125.0 cm/min)
Speed the mesh belt up from `80.0` to `125.0` cm/min (`B2 = 125`) without lengthening peak zones: Preheat Time E2 shrinks to `46.08` s (`Ramp = 2.82 °C/s` in E3), and Time Above Liquidus E4 drops to `40.32` s (`< 45` s minimum wetting time)—flagging `"OUT OF REFLOW WINDOW"` in E5!
=IF(ISTEXT(E2), E2, ROUND(B6 / (B2 / 60), 2))Try the example
Use the original values or change them to test your understanding.