Chip Lead Deformation Baking Solution

In the semiconductor manufacturing and electronics assembly industry, integrated circuit (IC) chips serve as core components, and their packaging quality directly impacts subsequent placement, soldering, and overall equipment reliability. During transportation, storage, and handling, factors such as external pressure, temperature/humidity fluctuations, or improper operation often lead to deformation issues in chip leads (e.g., bent, warped, or non-coplanar pins in QFP, SOP, PLCC packages). Lead deformation not only prevents pick-and-place machines from accurately handling chips but also causes defects like cold solder joints and bridging during reflow soldering, severely affecting production yield. To address this, a baking correction process is employed. By precisely controlling temperature and time, controlled stress release and plastic recovery of the lead material are achieved, restoring the original geometry and coplanarity.

Ⅰ.Chip Lead Deformation Baking Solution

 1. Problem Diagnosis and Pre-treatment

Before implementing the baking correction, a comprehensive assessment of the chip lead deformation status is required. Inspect the leads for bending, misalignment, breakage, or oxidation. Slightly bent leads can be restored via mechanical correction combined with baking; severely deformed or broken leads may require chip replacement or professional soldering repair. Additionally, check the integrity of the chip packaging and confirm the status of the Humidity Indicator Card (HIC) to determine if the chip has absorbed moisture. If moisture is detected, a dehumidification process must be performed prior to baking to prevent internal packaging stress caused by vaporization during high-temperature baking, which could exacerbate lead deformation or cause delamination damage.

2. Core Process of Baking Correction

The core of baking correction lies in utilizing the principle of thermal stress relaxation. By precisely controlling the temperature profile, the chip leads gradually recover their original shape under heat. The specific process flow is as follows:

• Preheating Stage:Place the chips to be processed in the preheating zone, set the temperature between 80°C and 100°C, and adjust the duration based on chip size and material properties. The purpose of preheating is to raise the overall chip temperature uniformly, reducing thermal shock during subsequent high-temperature baking and preventing new deformation or damage caused by excessive temperature differences.
• High-Temperature Baking Stage: Transfer the preheated chips to the baking zone, typically setting the temperature between 125°C and 150°C for a duration of 2 to 12 hours. This stage is critical for correcting lead deformation. The high-temperature environment allows internal stresses within the lead material to release. Combined with appropriate mechanical fixation or fixture constraints, the leads are guided back to their correct orientation. For BGA, QFP, and other package types, baking temperatures and times must strictly follow the device specifications to avoid exceeding material tolerance limits.
• Soaking and Cooling Stage: After baking, the chips must remain in a soaking zone for a period to ensure uniform internal and external lead temperatures, preventing secondary deformation caused by temperature differences. Subsequently, natural or forced cooling is performed. Rapid temperature drops should be avoided during cooling to prevent re-bending due to uneven thermal contraction.

3. Segmented Baking and Anti-Delamination Process

For specific specialized packaged chips, such as MEMS devices or those with complex lead frames, a segmented baking process is recommended:

• Raise the temperature to 100°C within 15 minutes and bake for 25 minutes.
• Raise the temperature to 150°C within 5 minutes and bake for 35 minutes.
• Lower the temperature to 70°C within 10 minutes before removal.

During segmented baking, an anti-delamination process must be adopted to ensure that the various layers of materials inside the chip remain tightly bonded during thermal expansion, avoiding positional offset of leads caused by delamination. Environmentally friendly molding compounds with matched coefficients of thermal expansion (CTE) and low water absorption rates should be selected to further reduce warpage risks.

4. Post-processing and Quality Verification

After baking correction, a comprehensive inspection of the chip leads is mandatory. Visual inspection confirms whether the leads have returned to a flat state, free of stains and damage. Electrical performance testing verifies lead connection reliability; if necessary, X-ray inspection or Automated Optical Inspection (AOI) can be utilized to detect potential internal defects. Corrected chips should undergo soldering or placement operations within the specified timeframe to prevent re-moisturization from prolonged air exposure.

Ⅱ.The Role of Baking in Chip Lead Deformation Correction

1. Moisture and Contaminant Removal:Chips easily absorb ambient moisture during storage and transport. During high-temperature soldering, this moisture rapidly vaporizes and expands, generating significant stress that can cause package cracking, lead deformation, or internal circuit damage. Baking evaporates internal moisture and removes surface oxides and contaminants, ensuring dry and clean lead surfaces for optimal soldering conditions.

2. Internal Stress Release: Differences in the coefficient of thermal expansion (CTE) exist between packaging materials and lead metals, creating internal stress during temperature fluctuations. Baking allows material molecular chains to rearrange at high temperatures, relaxing these stresses and eliminating lead warpage or deformation caused by stress accumulation.

3. Improved Solderability: Baking reduces surface oxides on chip leads, significantly improving wettability. Solder can better wet the lead surface, forming strong and reliable joints, thereby reducing the incidence of soldering defects like cold joints and bridging.

4. Stabilized Electrical Performance: The presence of moisture and contaminants affects chip electrical parameters and long-term stability. By removing these factors, the chip performs more stably during operation, contributing to the extended lifespan of the electronic product.

Ⅲ. Applicable Ovens for Chip Lead Deformation Correction Baking

1. Precision Hot Air Circulation Oven: Various oven types suit different baking scenarios and process requirements. For routine chip dehumidification baking, precision hot air circulation ovens utilize hot air systems to ensure uniform temperature distribution within the chamber. Temperature control accuracy is typically within ±1°C to ±2°C, supporting baking temperatures of 125°C to 150°C. These are suitable for conventional dehumidification of SOP, QFP, PLCC, BGA, and other packages. Ensure items are spaced apart and the exhaust valve is half-open to facilitate moisture expulsion.

2. Nitrogen Oven (Inert GasOven) : Designed for processes requiring high oxidation prevention. Nitrogen is continuously introduced during baking to displace air, creating an inert protective atmosphere. This effectively prevents pin oxidation and discoloration at high temperatures, maintaining the activity of metal surfaces—particularly suitable for gold-plated leads or chips made of easily oxidized materials.

3. Clean oven:Used for baking environments requiring high cleanliness. Certain semiconductor packaging processes require baking in Class 100 cleanroom environments to prevent particulate dust contamination. Clean ovens are equipped with HEPA filtration systems capable of filtering 0.3-micron diameter particles with 99.97% efficiency, achieving Class 100 cleanliness levels.

4. Vacuum oven:For scenarios demanding higher dehumidification efficiency. By evacuating the chamber to lower atmospheric pressure, moisture boils and evaporates at lower temperatures, accelerating the dehumidification process. This is particularly effective for devices with high Moisture Sensitivity Levels (MSL 5-6), shortening baking time without raising temperatures, thereby reducing potential thermal damage to chips. The vacuum environment also prevents lead oxidation during high temperatures.

Chip lead deformation is a critical factor affecting electronic product quality and reliability. A rational baking correction process can effectively restore lead morphology. Baking not only resolves warpage and delamination risks caused by moisture absorption through dehydration but also effectively improves lead coplanarity through stress release and thermal press shaping, while stabilizing packaging material performance and enhancing chip solderability and thermal reliability.