Chip High-Low Temperature Baking Standards

During the manufacturing, packaging, and placement of semiconductor chips, exposure to ambient air during production, transportation, and storage causes chips to absorb moisture. When a moist chip enters high-temperature processes like reflow soldering, the water inside the package vaporizes rapidly, generating significant internal steam pressure. This pressure can cause package delamination and cracking, or in severe cases, catastrophic chip explosion (popcorning). Instantaneous rupture under high temperatures leads to the total scrapping of the entire batch. Extended storage times, damaged vacuum packaging, or prolonged exposure after opening can lead to moisture absorption and oxidation, directly impacting electrical performance and solderability. High-low temperature baking removes residual moisture and volatile substances from within the package through controlled heating, ensuring chips remain dry, stable, and reliable in subsequent processes.

Ⅰ.Standards for Chip High-Low Temperature Baking

1. Low-Temperature Baking Range (40°C ~ 80°C):

Designed for highly thermally sensitive components, including micro-sensors, flexible PCBs, and high Moisture Sensitivity Level (MSL) chips. The standard process for reel-packed moisture-sensitive devices is 70°C for 24 hours to effectively remove adsorbed moisture from packaging. In a vacuum environment, the boiling point of water drops significantly, allowing low-stress removal of surface and shallow-layer moisture, preventing component aging or performance degradation caused by high heat. Common settings are 45°C, 60°C, and 70°C.

2. Medium-Temperature Baking Range (80°C ~ 150°C):

The mainstream dehumidification and pre-curing range for the vast majority of general-purpose chips. 100°C ~ 125°C is the standard baking temperature for ICs, discrete semiconductors, and ordinary packaged modules. For example, an MSL 3 IC with a thickness of 1.2mm that has been exposed for over 72 hours requires baking at 125°C ± 5°C for 9 hours if in a tray; if in a reel, it must be baked at 40°C with humidity ≤ 5% RH for up to 9 days. The 125°C ~ 150°C range is used for burn-in testing and deep outgassing of high-reliability general components. Equipment in this range requires temperature control accuracy of ±1°C to prevent parameter drift due to temperature fluctuations.

3. High-Temperature Baking Range (150°C ~ 600°C):

Enters the realm of precision curing and annealing.

• 150°C ~ 250°C: Suitable for optoelectronic components, epoxy-encapsulated chips, and silver paste curing modules; requires temperature uniformity ≤ ±1.5°C.
• 250°C ~ 400°C: Used for semiconductor packaging testing, ceramic substrate dehumidification, and metallization layer annealing. Ceramic-packaged military/aerospace-grade RF devices require baking/annealing at 300°C ~ 400°C.
• 400°C ~ 600°C: Adapted for large semiconductor component annealing and third-generation semiconductor (SiC/GaN) pretreatment. Requires high vacuum (≤ 1 Pa) and extreme temperature control precision (±0.1°C).

Ⅱ.Differences Between High and Low-Temperature Chip Baking

1. Objective:

• Low-Temperature Baking (40°C~125°C): Aims to "dehumidify." It evaporates and expels moisture from inside the chip and package gaps to prevent the "popcorn effect" (package cracking) during reflow.
• High-Temperature Baking (150°C ~ 600°C): Aims to "modify." It induces physical and chemical reactions such as recrystallization, thermal cross-linking, and lattice repair to enhance electrical performance and long-term reliability.

2. Temperature & Time Scale:

• Low-Temp: Completed within hours to tens of hours; temperature fluctuation control within ±5°C meets most requirements.
• High-Temp: Demands extreme precision—standard components need ±1°C, precision components need ±0.5°C, and ultra-high-temp processes need ±0.1°C. Often requires vacuum or inert gas environments, lasting from hours to days.

3. Atmosphere Requirements:

• Low-Temp Dehumidification (40°C ~ 150°C): Low vacuum (10 Pa ~ 100 Pa) is sufficient to lower the boiling point of water and accelerate evaporation.
• High-Temp Annealing (250°C ~ 600°C): Must use high vacuum (≤ 1 Pa) or nitrogen protection to prevent high-temperature oxidation and residual moisture. Otherwise, lattice defects and surface oxidation will destroy chip performance.

Ⅲ.Functions of Chip High-Low Temperature Baking

1. Eliminate Moisture & Prevent Popcorn Effect: Chips inevitably absorb atmospheric moisture during storage or transport. During high-temperature processes like reflow, vaporizing moisture expands, causing inflation, deformation, or cracking. Baking thoroughly expels this moisture, eliminating this fatal defect at the source.
2. Enhance Electrical Performance & Reliability: High-temperature baking promotes chemical reactions that optimize material properties. For instance, certain MOS devices see improved mobility and carrier lifetime; epoxy molding compounds show significantly increased bonding strength and thermal conductivity after curing at 175°C.
3. Relieve Internal Stress & Reduce Defects: Baking eliminates residual stress, reduces micro-cracks, and minimizes potential defects, extending service life. In semiconductor lithography, hard bake (post-bake) uses thermal cross-linking to form a 3D network structure in photoresist, greatly enhancing etch resistance.
4. Complete Key Process Curing: From LED encapsulant silicone curing (120°C ~ 150°C) to display panel adhesive curing (180°C ~ 220°C) and communication module burn-in testing, baking is an irreplaceable core step.

Ⅳ.When Do Chips Require Baking?

1. Expired After Opening:If an IC is exposed for more than 72 hours after unsealing, or if the Humidity Indicator Card (HIC) turns pink (≥10% humidity), baking is mandatory. For an MSL 3 BGA chip, 9 hours at 125°C or 9 days at 40°C/≤5% RH is required.
2. Exceeding Moisture Sensitivity Control Limits: Even if unopened, if the storage environment humidity exceeds 40% RH or exposure time exceeds 48 hours, the chip is considered moist and must be baked according to its MSL level. MSL 1 (e.g., CSP) has no limit; MSL 2 requires baking within 1 year; MSL 3~5 have floor lives of only 168~24 hours.
3. Failed Vacuum Packaging or Bulk Packaging: If the vacuum bag of a BGA chip is damaged, or if the chips are bulk-packed without vacuum, they face high moisture risk and must be baked before use.
4. Pre-Soldering PCBs: PCBs stored in >40% RH humidity or with expired HICs require baking at 105°C ± 5°C for 2~8 hours (lower limit for thin boards, upper limit for thick copper substrates) to prevent delamination and white spots during reflow.
5. Mandatory Requirements for High-Reliability Fields: Aerospace, automotive electronics, and military devices demand strict baking throughout the packaging, storage, and transport phases to ensure zero-failure operation in extreme environments. Automotive-grade chips often undergo three-temperature testing and reliability baking even during CP, FT, and SLT testing stages.

Ⅴ.Applicable Ovens for Chip High-Low Temperature Baking

1. Forced Convection Oven: Utilizes fans to circulate hot air for uniform heat transfer. Equipped with stainless steel heating tubes and intelligent PID controllers, these ovens offer good temperature uniformity. They are suitable for solder paste curing and general chip drying where extreme precision is not required. Accuracy is typically around ±5°C. They are cost-effective and meet basic needs.
2. Precision Oven:Offers significantly higher temperature control accuracy (up to ±1°C or better) with multi-segment programming and uniformity within ±1°C. Suitable for chip packaging and sensor burn-in testing. For precision processes like wafer baking and photoresist curing, precision ovens are mandatory.
3. Vacuum oven: Operates under negative pressure. The vacuum lowers the boiling point of water, facilitating volatilization and providing excellent drying results. The low oxygen environment prevents oxidation. However, due to the lack of convection media, temperature uniformity is relatively poor. Ideal for thermally sensitive or easily oxidized materials.
4. Nitrogen Oven:Fills the chamber with high-purity nitrogen (typically ≥ 99.999%) to provide a clean, oxygen-free constant temperature environment, effectively preventing oxidation during high-temperature baking. Widely used in semiconductor packaging and wafer baking. For flammable environments or anti-oxidation requirements, nitrogen or explosion-proof ovens are necessary.

Semiconductor chip high-low temperature baking is a precision process integrating dehumidification, pretreatment, and safety assurance. It plays a critical role in preventing the popcorn effect, ensuring solder joint reliability, and improving long-term chip lifespan. High-temperature baking (125°C ~ 150°C) excels in efficiency and thoroughness, suitable for rapid dehumidification of most conventional moisture-sensitive devices. Low-temperature baking (40°C ~ 90°C) offers safety and gentleness, ideal for fine processing of thermally sensitive structures and easily oxidized components. The necessity of baking depends on multiple factors, including the device's MSL level, floor life consumption status, HIC readings, and storage history.