Assuring the Integrity of Moisture-Sensitive Surface-Mount Devices (SMDs)

In order to produce advanced digital technology such as computers, smart phones, home electronics or specialized industrial automation, manufacturers rely on a highly specialized supply chain. One particularly important, and sensitive element of this supply chain involves the transport, protection and storage of moisture-sensitive surface mount devices, known as SMDs. This category includes many of the components which underpin today’s technology, such as powerful processors, chipsets and integrated circuits.

After their initial manufacture and testing, SMDs typically need to be transported to other sites. Here they undergo further processing, such as being assembled onto printed circuit boards, or placed directly into finished technology products. SMDs are connected using a process known as reflowing, during which the solder connections of the SMD are heated until they liquefy and flow. After this, they cool and create solid bonds with a substrate, for example a printed circuit board.

Many SMDs – and their reflowable solder connections – are extremely moisture-sensitive. If any excess moisture is present in SMDs during the high temperature treatment steps associated with reflow processing, either the SMDs themselves or their solder connections can fail. This device failure can occur in a variety of ways, such as delamination, cracking and “popcorning”, among others.

As a means to minimize or eliminate these problems, a set of industry standards have been established which classify SMDs according to their moisture sensitivity, provide them with packaging which protects against moisture, and eliminate any excess moisture from SMDs before reflow processing is carried out. The standard moisture sensitivity levels (MSLs) for SMDs are defined as part of the joint IPC/JEDEC standard, J-STD-020, which grades moisture sensitivity in levels, ranging from level 2 (least moisture sensitive) to level 6 (most moisture sensitive).

Another standard, IPC/JEDEC J-STD-033, “Handling, Packing, Shipping and Use of Moisture/Reflow and/or Process Sensitive Devices”, defines the industry guidelines for the dry packaging of moisture-sensitive, reflowable SMDs. It requires that moisture-barrier bags, known as MBBs or “dry packs” used to contain SMD’s provide a shelf life of at least 12 months, and that they contain both a humidity indicator card (HIC) and an active desiccant packet. The HIC has historically been used to give a visual indication of the humidity level in the dry packs at the time of opening.

Illustrative example of a dry pack configuration for Moisture Sensitive Devices (MSDs) using Clariant’s Humitector™ Type 2 Non-Reversible Humidity Indicator Card and a Desi Pak® desiccant bag.

Illustrative example of a dry pack configuration for Moisture Sensitive Devices (MSDs) using Clariant’s Humitector™ Type 2 Non-Reversible Humidity Indicator Card and a Desi Pak® desiccant bag.

In undamaged and correctly sealed dry packs, HICs are typically assumed to be reliable indicators that the packaged SMD has not been damaged as a result of exposure to high humidity. Until recently, HICs used in dry packs have been of a single type: “reversible.” These reversible HICs usually offer three reversible humidity indicators, which change color as a result of exposure to 5%, 10% and 60% humidity. These reversible HICs have a good track record of reliability when dry packs remain properly sealed and undamaged.

In certain situations, however, reversible HICs can fail to indicate actual humidity exposures. For example, if the seal of a dry pack is defective, improper, or damaged, exposure to high humidity (>60%) can occur. While the reversible HIC would register the change of humidity in the bag as a color change (to pink – indicating that the contents have been wet) on the 60% indicator, the reversible 60% spot would change color back to black or blue, indicating low humidity. If the damaged pack were returned to a low humidity environment for a prolonged period, no indication of the earlier high humidity exposure level would be seen, and thus, possible damage to the SMD could be missed.

Clear indication of exposure to high humidity is critically important for SMDs with high moisture sensitivity (Level 2 or greater, as defined in J-STD-020). Customers must be able to rely on clear and accurate humidity indication as an assurance of the quality of an SMD and its fitness for processing and further use. Without it, they could unknowingly accept SMDs that have been irreparably damaged by moisture during storage or transit.

Alternatively, they might approve SMDs that have not been sufficiently heat-dried for processing. Besides the processing questions, there are financial issues: For example, determining the origin of the dry pack problems and who — supplier, customer, or shipper—is financially responsible for the damaged SMDs.

A New Solution– the Humitector™ Type 2 “non-reversible” Humidity Indicator Card

In response to the limitations of “reversible” HICs, certain customers and SMD suppliers have asked for improvements to humidity indicator cards. In particular, they have asked for an updated HIC that could provide a more complete history of exposure to moisture and SMD integrity within dry packs.

To address these concerns, the originator of the color change humidity indicator card, and member of the JEDEC’s Subcommittee 14.1, “Reliability and Test Methods for Packaged Devices”, Clariant, has created a new “non-reversible” low-halogen and cobalt dichloride free humidity indicator card.

This HIC combines two reversible indicators for lower humidity exposure (5% and 10%) with the new non-reversible (60% RH) indicator spot, as shown in Figure 1. The 5% and 10% reversible spots function in the same way as similar indicators, changing color from blue (dry) to lavender, to pink (wet) to show humidity exposure at the levels indicated. If humidity levels drop, the 5% and 10% indicators will gradually revert back to blue.

Humitector™ Type 2 Non-Reversible Humidity Indicator Card

Figure 1. Humitector™ Type 2 Non-Reversible Humidity Indicator Card

The new, non-reversible 60% spot, however, works differently. Instead of changing color from blue through to pink as the 60% indicator on a reversible HIC would, the non-reversible 60% humidity indicator stays blue, but if it is exposed to humidity over a prolonged period of time it starts to liquefy and spread until it overruns (migrates) beyond its black indicator circle as shown in Figure 2.

Humitector™ Type 2 Non-Reversible Humidity Indicator Card - exposed to humidity for a prolonged period of time

Figure 2. Humitector™ Type 2 Non-Reversible Humidity Indicator Card - exposed to humidity for
a prolonged period of time

Even if the humidity level is later reduced, such as during extended storage in dry conditions that cause reversible indicators to revert back to blue, the migration of the non-reversible blue spot on the new HIC remains. This provides a reliable, and permanent indication of the prolonged high humidity conditions that could have affected the package and its contents during storage.

A Change to Packaging Standards

Having considered the function and benefits of Clariant’s non-reversible HIC, IPC and JEDEC have revised and approved a new joint standard, J-STD-033 (Revision D), allowing its use. This revised standard allows the use of both types of HIC cards in dry packs. To prevent confusion, the new revised J-STD-033 redefines HICs into two types. The conventional reversible HICs are redefined as “Type 1 – Reversible,” while the newer non-reversible cards have been introduced as “Type 2 – Non-Reversible.” Beyond this reclassification, the revision makes no changes regarding the use of Type 1 reversible cards.

Users of the new Type 2 non-reversible cards will find that they can be handled and used in the same way as Type 1 cards, with one exception: Type 2 cards must be kept in their original manufacturer packaging (i.e. shrink-wrapped) until they are opened for use. Once they are opened, prolonged exposure to high humidity in the ambient environment could result in the activation of the non-reversible 60% indicator spot, rendering it useless in the dry pack environment.

Previous revisions have allowed for the re-use of reversible Type 1 HICs so long as the 60% humidity indicators have not changed color. The latest standard allows for the re-use of both Type 1 and Type 2 HICs under the same circumstances, however the re-use of either type is now prevented if the 60% humidity indicator has changed, as this can affect the accuracy of the other indicators.

The use of Type 2 HICs with a non-reversible 60% spot indicator is preferred by IPC/JEDEC standard J-STD-033D.

This information has been sourced, reviewed and adapted from materials provided by Clariant Corporation.

For more information on this source, please visit Clariant Corporation.

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