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Printed circuit boards (PCBs) rely on various processes for reliability, with PCB baking standing out for its role in eliminating defects and enhancing performance. This process safeguards delicate PCBs from delamination, ensuring top-quality electronic assembly solutions. Delve into the mechanics of PCB baking to understand its significance in ensuring optimal PCB functionality.
Table of Contents
What is PCB Baking?
PCB baking serves to eliminate moisture from printed circuit boards (PCBs). As PCB surfaces cool below surrounding air temperatures, they draw in moisture, which, if left unaddressed, can form steam during processing, potentially damaging the board or disrupting circuits. The degree of moisture retention varies depending on the composite materials used in the PCB. For instance, Polyimide flex and rigid materials tend to absorb more moisture than FR4 panels.
How does PCB baking work?
During PCB baking, the oven heats the board within a temperature range of 100°C to 130°C, evaporating moisture. However, temperature monitoring is critical to prevent overheating, which can harm the PCB. Monitoring the board’s weight verifies moisture removal. A key objective of PCB baking is to prevent delamination, a problem occurring when moisture escapes through copper via holes. In multi-layer panels, moisture accumulation in holes or at epoxy-composite junctions can lead to delamination or “measling.”
Why are PCBs baked?
Baking circuit boards serves multiple purposes, including preventing condensation from exiting through copper-coated gaps and limiting outgassing, which can lead to blowholes or pinholes and affect soldering quality. It also guards against delamination or measling during solder adjustments. While modern surface treatments and copper layers typically ensure a strong bond, drilling or mechanical actions can still cause damage to the bond between the glass fabric and epoxy. Although not all PCBs require baking, it’s crucial for PCB assembly companies to remove moisture to ensure proper equipment functionality.
Conditions for Effective PCB Baking
PCB baking proves effective in moisture mitigation, with specific steps crucial for optimal outcomes, especially with OSP surface finish. For short-term storage (up to 2 months), bake at 120°C for one hour, while medium-term storage (up to 12 months) requires a two-hour bake at the same temperature. Extended storage (6-12 months post-production) necessitates a four-hour bake, while longer storage (>12 months) demands six hours at 120°C. However, prolonged storage may compromise PCB layers, affecting performance and necessitating surface finish alterations.
Rigid PCB Process for Various Surface Finishes: ENIG, HASL, Lead-Free HASL
Regardless of thickness, all PCBs are baked for at least 2 hours at 120°C. The time interval between baking and soldering depends on storage conditions. Under 50% relative humidity, the suggested maximum hold time is 8 hours. However, maintaining boards in an oven at 35°C can extend this duration beyond the standard.
Purpose of Baking Process for Components
The primary goal of the baking process is to eliminate moisture from specific electronic devices, particularly those labeled as moisture-sensitive parts. Moisture-sensitive plastic packaging can pose a significant risk as it absorbs water when circuit boards are being assembled. During reflow soldering, this absorbed moisture can lead to catastrophic outcomes due to the elevated temperatures, forming water bubbles within the packaging. This expansion can damage internal components. Moisture sensitivity also reduces the shelf life of components, with higher sensitivity levels resulting in quicker water absorption and diminished longevity.
source: https://www.myemssolutions.com/what-is-pcb-baking-and-should-you-use-it/
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