Moisture sensitivity in electronics

At the heart of electronics devices are a wide range of components. Component types include semiconductors (transistors, diodes integrated circuits, passive (resistors, capacitors, inductors), sensors (position, motion, force, thermal magnetic etc), and display (such as LEDs). One thing that most of these component types, is they are made of substrate materials that are hygroscopic in nature, meaning they can absorb moisture.

Electronic components are usually encapsulated in a plastic casing to prevent the ingress of foreign materials, including moisture. However, the casing can be permeable to moisture over time or have joints that are not perfectly sealed. When these components are exposed to air they can absorb the moisture into the substrates.

This absorption of moisture does not normally affect the operation of the component but can become a problem when it is subjected to high temperatures during the manufacturing process (reflow, wave etc).

Some of these processes can exceed 240 degrees Celsius. These high temperatures and large localized temperature changes can cause the absorbed moisture to rapidly expand causing delamination of the substrate, damaging the component. This delamination can render it inoperable or worse, shorten its lifespan so that it fails in the field early.

When damage is minor, it is impossible to detect from a practical viewpoint. Therefore, we aim to prevent damage in the first place. The industry has developed a clearly defined process for managing moisture in electronics.

Industry Standards

The first step involves a rating system which classifies the sensitivity of the component to potential damage. The sensitivity varies depending on the materials used in the component. Eight levels are set out in the IPC-M-109 standard, defining how long a component can safely be exposed to the environment (air). The levels range from MSL 1 (unlimited exposure) through MSL 3 (168 hours) to MSL 6, which requires mandatory baking before use.

Baking at a low temperature will safely evaporate any absorbed moisture and this can be used to “reset” the clock for components at other MSL levels.

Another standard (IPC/JEDEC J-STD-033C-1) sets out the processes for safely handling, packing, shipping and use of moisture sensitive components.

Best practices at Circuitwise

Circuitwise requires designers to specify the MSL level of every component above MSL level 3 and then requires component suppliers to adhere to the relevant processes set out in the handling standard.

At our inward goods inspection, we check to ensure components are packaged correctly (typically in a moisture barrier bag with a desiccant and moisture indicator card included - and labelled correctly (indicating when the components/bag was sealed and the Moisture Sensitivity Level of the components).

Electronic components in our Dry Cabinet with moisture barrier bags

The components are then stored in our dry cabinet which keeps the components at less than 10% humidity. When components are removed from this cabinet, the action is logged and again on return to the cabinet. In this way, we can track the cumulative exposure to air.

If components are reaching their maximum floor life, then we can bake the components at a low temperature to “reset” the exposure time to zero, or responsibly dispose of the components if they are no longer required.

Once the components have been through the reflow oven it is no longer necessary to control the exposure of the components, as it will not ever be exposed to extremely high temperatures again.

If a product is returned or needs rework, we subject the board to the baking process to ensure that all moisture has been removed before any reheating on our dedicated rework station (which can heat a single component typically a BGA).

Circuitwise’s inventory management system logs all of these steps, thus providing quality assurance that moisture sensitive components are being handled responsibly. This is particularly important for high-reliability devices such as those used in mining, aerospace and MedTech.

Circuitwise Electronics Manufacturing, Sydney Australia

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