• Control of Moisture Sensitive Devices (MSDs)

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    Introduction

    An MSD is an electronic component, packaged within plastic, that can absorb moisture due to the permeable nature of the encasement. When rapidly heated, entrapped moisture can expand and cause damage. This damage may not be visible and a component or finished assembly may even pass the electrical test, however, still experience a field failure. These latent failures, such as Surface Peeling, Popcorn Effect, and Microcracking, can be catastrophic and potentially root cause may be non-detectible as components and assemblies are sometimes destroyed upon failure. Demand for smaller, lightweight components, with thinner plastic packaging, adds to moisture absorption concerns. Factor in manufacturing using higher reflow temperatures (Lead-Free Solder Alloys) in high humidity regions of the world, and it becomes clearer that proper handling and storage of MSD is extremely critical.

    If you work in an environment that distributes electronic components or manufactures assemblies with MSDs, this article will be important to you as many of these requirements are simply not followed correctly. One of the shortest and most misunderstood documents, relative to MSD, is Handling, Packing, Shipping and Use of Moisture, Reflow, and Process Sensitive Devices IPC/JEDEC J-STD-033D April 2018 (J-STD-033D). This leads to poor process planning, incorrect controls, and ultimately potential field failures. Additionally, MSD controls are some of the most common audit findings.

    J-STD-033D may appear to be an intimidating 32 paged document, however, there are basically 10 pages to focus on. To understand the requirements, start at Section 3 Dry Packaging, and end your review after Section 6 Board Rework.

    Read Section 7 and Table 7-1 only if you wish to control your factory different than the standard temperature of <30C and Relative Humidity (RH) <60%. Simplifying still further, 4 of those 10 pages are pictures and tables. This article will highlight important aspects of the J-STD-033D, clarify some misunderstood sections, and share some best practices to enhance your MSD controls.

    FLOOR LIFE

    MSDs are classified into 8 categories, Moisture Sensitivity Level (MSL) 1-6. Moisture sensitivity increases with MSL # and floor life decreases as defined in Figure 1, Table 5-1 of J-STD-033D.

    ENVIRONMENTAL CONTROLS

    It is important to ensure that all areas of the factory where MSDs are exposed to the environment are controlled at <30C and <60% RH. Exposed to the environment means removed from a Moisture Barrier Bag (MBB) or Dry Cabinet. As mentioned previously, if your organization is not able to maintain these conditions, refer to Section 7 of J-STD-033D and be prepared to adjust (shorten) floor life of MSDs. Areas include but are not limited to; Quality (Incoming Inspection) and Operations (Kitting, Reflow Soldering, and Rework). Control of storage areas, for sealed MBBs, is documented on the MBB Label Figure 2.

    MONITORING FLOOR LIFE

    Since MSDs are sensitive to humidity and require floor life controls, there should be a method to ensure exposure time is not exceeded. This is normally accomplished either manually using a MBB label or electronically by scanning a bar code label (Font 39M provides a human readable label) on an MBB. In either case, at no time should an MSD be exposed to the factory environment while the tracking system indicates that it’s not being exposed. Therefore, the order of processing should look like this.

    • Annotate MBB as Opened.
    • Inspect contents of MBB, Humidity Indicator Card (HIC), and perform operation as required.

    • Close (Seal) MBB using new or reactivated desiccant. A full vacuum seal is not acceptable.
    • Annotate MBB as Closed (Sealed).

    Proper storage and handling of MSDs, within a MBB or Dry Cabinet will prevent issues, however if an issue is observed, a qualified person should be notified for disposition. Some of those issues include conditions where a MSD exceeded temperature or humidity requirements, a HIC that shows “wet” (“Not Blue” or “Pink”) relative to the 10% or 60% dot per MSL, or a Dry Cabinet which is not functioning properly. One should not assume that reconditioning an MSD is the solution.

    For example, an operator who had opened a MBB with MSL 3 parts noticed the 5 and 10% dots were both “Pink” and the 60% dot was “Blue”. A new engineer had identified the components to be reconditioned, however upon further review it was determined that the MBB had been improperly sealed the prior evening. Floor life for MSL is 168 hours. These parts only had 22 hours of expo-sure time. Since they had remained in the operations area during the evening, the solution was to annotate on the MBB label an additional 16 hours of exposure (the time between sealing and opening). These MSDs still had 130 hours of floor life remaining. Subjecting MSDs to unnecessary extra processing are a waste of time and money which could also cause a quality issue due to handling and baking.

    Another aspect of floor life, which isoften o verlooked, is when multiple reflow cycles are used. J-STD-033D covers this in Sections 5.4.4 and 6.2. After the initial reflow process, the assembly will need to be processed through additional thermal cycle(s) prior to exceeding the floor life of any individual MSD on that assembly.

    HUMIDITY INDICATOR CARD PERJ-STD-0 33D

    Noteworthy is the ability to interpret the HIC, Figure 3. This has proven to be

    a challenge in most organizations that I have visited. I attribute this to several things including a poorly worded HIC and inadequate training. Additionally, Table 3-2 in J-STD-033D explains the HIC upside-down and doesn’t include all conditions. For example, for values between 5-10% RH. A best practice after

    opening a MBB and when evaluating aHIC, I s to ignore the 5% dot. The wording on the card is much less confusing when focusing on the appropriate 10% or 60% dot, based on the MSL. The 5% dot will always be “Pink” when the 10% is “Not Blue” or “Pink”. And if the 5% dot is “Blue”, then surely the 10% will be “Blue”, so forget about the 5% dot! The 5% dot simply does not matter unless it is used as a double check Dry Cabinet controls or used to monitor desiccant storage. Less common are Cobalt-Free HICs which use 2 different colors to indicate dry/wet conditions.

    Through the years, I have trained many on how to read a HIC. Later I developed a simplified chart, Figure 4, to interpret a HIC. In this chart, under the dot with a P is “Not Blue” as the color of the dots transition from “Blue” to “Pink”, they initially turn “Not Blue”. At the bottom of this chart is proper storage condition for Desiccants at <5% RH. If there is one take-away from this article, it should be to develop your own HIC interpretation chart for everyone who works with MSDs.

    DESICCANTS PER MIL-D-3464 TYPE II

    When sealing a MBB and determining the amount of desiccant to use, J-STD-033D Section 3.3.2.2.1 has a formula, Figure 5, to aid in the calculation. Simplifying the “Units” of desiccants to be placed into a MBB can prevent issues. Best practice is to have a work instruction defining Units of desiccants for each bag size. Many companies have 4-6 different bag sizes, which makes includingthe formula unnecessary. Having a single

    sized desiccant is also a best practice, perhaps a 1 Unit or 2 Unit based on the size of your carriers/reels. Easy to add 1 or 2 of these to fulfill a requirement. Some organizations have 1/6 Unit desiccants and need to place 12 of these in large MBBs requiring 2 Units of desiccants. 1 or 2 larger desiccant bags vs. 12 smaller desiccant bags. The choice seems clear in Figure 6.

    Desiccants can be reactivated an unlimited number of times by baking at 245F for 16 hours. Maintain fresh (new) desiccants in a container, Figure 7, that can be resealed. Tape a HIC on the inside of the lid, no tape on the dots, with the dots facing away from the lid, Figure 8. Each time the container is opened to remove desiccants for dry packing, the HIC should be viewed. All dots “Blue” equals acceptable. Upon opening an MBB, place spent/used desiccants into a container, Figure 9, with a slot cut into it. This container should be clearly identified. When you run low on fresh desiccants, simply reactivate the spent ones … instructions on desiccant bags and above.

    MOISTURE BARRIER BAGS PER MIL-PRF-81705 TYPE I

    These will appear metallic and should be identified/traceable to the standard as well as their capability relative to their Water Vapor Transfer Rate (WVTR) which is normally on the supplier’s technical data sheet. Be cautious of thinner MBBs which have high WVTRs and do not meet requirements. These will generally be less expensive, however are not acceptable.

    PAUSING FLOOR LIFE

    MSDs sealed in an MBB, with fresh desiccant, will stop/pause floor life. The other method to stop/pause floor life is the use of a Dry Cabinet (Dry Box). Dry Cabinets should be maintained at <5% RH for unlimited storage of MSDs. If your organization does not deal with MSL 4, 5 and 5a, then control at <10% RH is acceptable for unlimited storage of less sensitive MSDs (MSL 2, 2a, and 3). Placing a HIC within the Dry Cabinet, against the glass facing outwards, can provide a secondary visual reference for operators to ensure the Dry Cabinet is operating properly. Many newer dry boxes operate at higher temperatures, close to 40C and have Humidity Gauges as well. Dry Cabinets that operate at 40-45C can be used to recondition MSDs to reset floor life. Some organizations store Printed Circuit Boards (PCBs) in Dry Cabinets at <10% RH. PCBs are not defined within J-STD-033D, so no further comments will be made regarding baking or other prep for soldering. Desiccants may also be stored in Dry Cabinets when controlled at <5% RH. J-STD-033D Table 4-3 is for users and should contain another row for MSL 4, 5, and 5a that provides for pausing the floor life in a Dry Cabinet at <5% RH. This is missing from Section 4.1.2.2, however later defined in Section 5.3.3.2 that states, “SMD packages not sealed in a MBB may be placed in a dry atmosphere cabinet, maintained at not greater than 5% RH. Storage in these dry cabinets may be considered equivalent to storage in a dry pack with unlimited shelf life.” So Dry Cabinet at <5% RH is equivalent to an MBB.

    1. Surface Mount Device (SMD) =MSD
    2. Dry Atmosphere Cabinet = Dry Cabinet
    3. Dry Pack = MBB.

    Noteworthy is J-STD-033D Section 5.3.3.1 which states that a Dry Cabinet at <10% RH is not equivalent to an MBB. However, Section 4.1.2.1 states that MSL 2-3, in a Dry Cabinet, will stop/pause
    floor life.

    RESETTING FLOOR LIFE

    Reconditioning MSDs refers to resetting he floor life. There are two methods. The first, and least used, is defined in the J-STD-033D Section 4.1.2 Short Duration Exposure. The best practice to use here is software (vs. manually calculating) and utilizes Dry Cabinets. The second method requires oven baking at low humidity levels per Table 4-1 of J-STD-033D. The table is easy to interpret, however when changes had been made from past revisions of the standard some opportunities to make errors surfaced. Originally there were stated temperatures for baking, such as 40C, 90C and 125C. Tolerances were later added, however they were single sided. 125 +10 -0C became the new specification, however many processes remained with oven set points of 125C. Easier to simply have stated 130 +/- 5C, however the thought is to keep the temperature as low as possible and stay between 125-135C. Similar single sided tolerances now exist for 90C and 40C bakes. Take noteand adjust you r ovens appropriately based on oven capabilities. J-STD-033D Table 4-2 is for Suppliers, and they should also be aware of single sided tolerances. J-STD-033D Section 4.2 is worth the short read as it covers different carriers and limitations as well as venting of ovens and <5% RH requirements. A concern iswhen ovens are  used for multiple applications. Be cautious of cross contamination which could lead to solderability issues.

    BUYER BEWARE

    Organizations have a responsibility to flow down specific requirements on purchase orders to suppliers and should not assume that these suppliers or distributors understand J-STD-033D and other applicable documents. Here are several examples of noncompliant materials observed in electronic component distributor and assembly facilities.

    1. HICs be per J-STD-033D. Incorrect HICs have been observed in numerous facilities. Some examples are shown below with reasons why they are Not Acceptable.

    Figure 10 & 11, these types normally arrive in a container of fresh desiccants and sometimes are at the very bottom, not even visible. The job of a desiccant is to maintain a sealed MBB <10% RH for up to 12 months. Having the dryest desiccants possible is the reason behind storing desiccants with a J-STD-033D HIC at <5%

    RH inside the lid, so it’s visible. Storage up to 8% RH is not recommended. Figures 12 & 13, these unacceptable HICs have no place in a facility that needs to control MSDs.

    Figures 14, 15, & 16, these unacceptable HICs have no place in our facilities as well. These HICs are actually dangerous as they provide instructions to examine product or change desiccant that is not relevent to MSD control. Figure 17, this was an alarming issue discovered when 2 (on the right) HICs

    were removed from the factory floor and in an atmosphere that was close to 45% RH. None of the cards’ dots had turned pink, while the J-STD-033D HIC (on the left) had indicated > 10% RH. Not just the wrong 2 HICs in use, these were defective as no dots turned color.

    2. Desiccants shall be per MIL-D-3464 Type II and be identified with the Units relative to its drying capacity.

    Figure 18, an Acceptable desiccant. 2 Unit size. Labeled with specification andreact ivation time and temperature.

    Figures 19, 20, and 21 provide 3 examples of unacceptable desiccant bags. Noreferenc e to specification or size (Unit).

    Figure 22, shows inadequate storage ofdesicca nts. This open container was found in the corner of the workspace. Completely

    open/exposed to the room environment. These individuals lacked both training and basic understanding of these requirements and reason for using desiccants.

    3. Moisture Barrier Bags are per MIL-PRF-81705 Type I. Below are some examples of poorly packaged product.

    Figure 23, although some assembly facilities require PCBs to be shipped in MBBs with desiccants and HICs, there’s presently no industry requirement for this. Save time and money and don’t use non-compliant desiccant bags and HICs with plastic packaging that provides very little moisture protection. HIC and desiccants, placed directly in contact with product in generally unacceptable.

    Figure 24, the MBB label should identify the MSL of the parts. The empty box is unacceptable. To facilitate proper tracking of floor life, the MSL needs to be known. Figure 25, this is an example of a poorly sealed MBB. The top of the left side is not sealed and when this bag was completely opened, the HIC had both 5 & 10% dots wet indicating unacceptable. Additional processing was required to reset the floor life of these MSDs for inadequate sealing operation, thus creating potential quality issues.

    Conclusion

    Procedures, work instructions, and other documents for the control of MSD should be straightforward and provide sufficient information for operators, inspectors, and engineers to perform their specific functions. Bake tables, desiccant calculation formula, and other requirements are best left out of internal documents and simply referenced. This will keep the length of your documents down, allow training on important controls and not cause unnecessary revisions to internal documentation when J-STD-033D changes. Including these requirements within a Control Plan will help ensure compliance with internal handling and storage of MSDs as well as provide the end users with the most reliable product possible. The purpose of writing this article was to provide a clearer vision (2020 perhaps) of the requirements for proper MSD Controls. I challenge you, the reader, to go out onto your or your supplier’s factory floor and observe the controls. Look for a Control Plan. Review how MBBs are opened and how HICs are interpreted.

    Review bake logs, floor life tracking and the types of materials used within the process. I’ve challenged myself to join the J-STD-033 committee and work with them to further enhance and simplify this very important standard. For in the end, this is about product reliability for our clients and zero field failures relative to improper Control of MSDs.

     

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