Moisture can be most overlooked as a key risk in electronics assembly. It causes no visible damage during storage, gives no warning before a board goes through a reflow oven but it accounts for a large number of field failures and rework costs.

Knowing the risks of moisture sensitivity levels (MSL) is essential for anyone handling surface mount electronic components as it is a basic requirement for protecting the integrity of every build. At Princeps, we are experts in supply chain security, as well as the sourcing and testing of electronic parts and we are going to guide you through the essentials of MSL.

What Is Moisture Sensitivity?

Many surface mount devices such as plastic encapsulated ICs, BGAs and QFPs can absorb ambient moisture through their packaging. When a part that contains trapped moisture enters a reflow oven the moisture quickly vaporises. The pressure can crack the package, delaminate internal interfaces or damage bond wires. This failure mode is often called popcorning because of the distinct cracking sound it can produce.

The IPC/JEDEC J-STD-020 standard places components on a scale from MSL 1 to 6. This means that MSL 1 has unlimited floor life at standard conditions and MSL 6 needs baking immediately before use.

  • MSL 1 - unlimited floor life - no special precautions needed
  • MSL 2 - up to 12 months floor life at ≤30°C / ≤60% RH
  • MSL 2a - up to 4 weeks floor life
  • MSL 3 - up to 168 hours (one week) floor life
  • MSL 4 - up to 72 hours floor life
  • MSL 5/5a - 48 or 24 hours floor life
  • MSL 6 - compulsory bake before every reflow

Floor life starts at the moment a sealed moisture barrier bag (MBB) is opened. Once the clock begins it does not pause unless the part is returned to a controlled dry environment.

Handling & Storage In Practice

Dry cabinets set to ≤10% RH effectively pause floor life build up making them the most practical tool for busy production lines. As an alternative, electronic parts can be resealed in MBBs with a new desiccant and a new humidity indicator card (HIC). The HIC should read safe (generally less than 10–30% RH depending on the type of card) before the bag is then sealed.

When components are delivered from a distributor, be sure to check the bag for perforation, assess the HIC reading and record the open date. These three steps take less than a minute and can prevent a large amount of avoidable rework.

If floor life has been exceeded then baking at the temperature and duration listed in J-STD-033 restores the component to its dry standard. Common profiles run at 125°C for 24 hours for most plastic packages, however, temperature sensitive parts may require a bake with a lower temperature and a longer time duration.

Why Part Sourcing Is Just As Vital As Handling

The right handling provides value only if the components themselves are genuine. Counterfeit or re marked parts may carry forged MSL labels, faulty packaging and unknown moisture history. Sourcing parts from a trusted and authorised distributor who keeps traceability from manufacturer through to delivery, means that the MSL details on the label match the component inside.

Here at Princeps, components are sourced globally with traceability and quality in house lab inspection, so that your team can apply the correct MSL handling. If you would like to find out more about our supply chain security services, get in touch to discuss your requirements with our expert team.