Baking during PCB production is a key process to ensure reliability, mainly addressing issues of moisture, stress, and material stability. The following is an analysis of scientific basis and engineering necessity:
Table of Contents
1、 Core reason: Eliminating fatal defects caused by moisture
1. Prevent the ‘Popcorn Effect’
-Mechanism: After moisture absorption, the multi-layer semi cured sheet (Prepreg) vaporizes water under high temperature (>220 ℃) reflow soldering → the vapor pressure breaks through the laminated structure → the inner layer separates or bulges.
-Data: FR-4 with a moisture content greater than 0.2% has a vapor pressure of 4MPa at 260 ℃, far exceeding the copper resin bond strength (1.5MPa).
-Baking scheme: 120 ℃/4h pre baking to reduce the moisture content to<0.05% (IPC-1601 standard).
2. Inhibit CAF (conductive anode wire)
-Mechanism: Moisture+ion residue+electric field → copper ions migrate along the glass fiber → short circuit inside the board.
-Baking effect: Cut off the source of electrolyte and reduce the risk of CAF by 70% (IPC-TR-468 study).
2、 Material stability optimization
1. Enhance the curing degree of resin
-Problem: Some epoxy resins have insufficient curing degree (<90%) → Tg decreases and Z-axis expands at high temperatures.
-Baking scheme: cure at 170 ℃/2h to achieve a curing degree>95% and increase Tg by 8-10 ℃ (IPC-4101 validation).
2. Eliminate internal stress
-Cutting/drilling stress: Mechanical processing causes microcracks in the substrate, and moisture intrusion exacerbates crack propagation.
-Baking effect: Annealing at 120 ℃/1h releases stress and reduces the crack rate of pore walls by 40%.
3、 Process adaptability requirements
1. Preparation before special surface treatment
| Process | Baking conditions | Purpose |
| OSP | 150 ℃/30min | Remove oxide layer and enhance organic film adhesion |
| Sinking gold | 120 ℃/1h | Prevent micro pores and bubbles from causing missed plating |
| Tin spraying | 100 ℃/2h | Reduce tin pits (Void) |
2. Protection of moisture sensitive components (MSD)
-Bake activated dry packaging: Bake at 40 ℃/10% RH to restore workshop life (Per J-STD-033B).
-Dehumidification before repair: 125 ℃/8h (for MSL Level 4 BGA).
4、 The risk of improper baking and precise control
The consequences of excessive baking
-Resin aging: Accumulated over 48 hours at 150 ℃ → resin embrittlement, with a 30% decrease in impact toughness.
-Copper foil oxidation: Bake in air above 130 ℃ → Copper surface generates Cu ₂ O, deteriorating weldability.
5、 Industry Trend: Intelligent Baking Technology
1. Vacuum low-temperature baking: Bake in an environment of 70 ℃/10Pa, which increases the efficiency of moisture removal by three times and avoids oxidation.
2. Infrared online monitoring: Real time feedback on the moisture content of the board, dynamically adjusting the baking time (with an accuracy of ± 5%).
3. Blockchain traceability: Baking parameters are stored on chain to meet the traceability requirements of automotive electronics IATF 16949.
Conclusion: Baking is the art of balancing cost and reliability
-Must be baked: boards stored in high humidity environments (>60% RH), multi-layer inner layers, thick copper plates (>3oz).
-Can be omitted: Double sided panels with vacuum packaging and moisture content<0.1%.
-Golden Rule: Follow the principle of “testing first, baking later” and customize the process based on IPC-1601.
The following will give you the PCB baking instructions for your reference:
1. If the PCB is unpacked for more than 5 days within 2 months of the manufacturing date, please bake it at 120 ±5°C for 1 hour before SMT assembly;
2. If the PCB is over 2 months from the manufacturing date, please bake it at 120 ±5°C for 1 hour before SMT assembly;
3. If the PCB is 2 to 6 months from the manufacturing date, please bake it at 120 ±5°C for 2 hours before SMT assembly;
4. If the PCB is over 6 months to 1 year from the manufacturing date, please bake it at 120 ±5°C for 4 hours before SMT assembly;
5. The baked PCB must be used up within 5 days (put into IR reflow), and if can not be used up within 5days, the remaining PCBs will need to be baked for another hour before SMT assembly;
6. If the PCB is more than one year from the manufacturing date, please bake it at 120 ±5°C for 4 hours before SMT assembly. Better is send it to the PCB factory to re-make surface treatment before SMT assembly.
Get your exclusive quote immediately: fill out the form or send an email directly, and we will provide you with a quote service within 24 hours. Enjoy free DFM optimization and a 10% discount on SMT patches for your first order!
