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September, 2020


Component Dry Storage: Separating Fact from Fiction By Mark Waterman, Electronics Division Manager, ECD


are, however, some common misconceptions about drying components and the best methods to con- firm that moisture-sensitive devices (MSDs) are ready for soldering. IPC J-STD-033 governs han- dling procedures and processes for MSDs, but the standard can be hard to apply.


M


Pausing vs. Resetting Floor Life Placing components in dry storage to


reset their floor life clock is a misconception. It is important to distinguish between “pausing” versus “resetting” component floor life. Baking a set of components at sufficient tem- perature for an appropriate length of time will reset their floor life. The schedule for perform- ing a compliant bake is detailed in Table 4-1 of J-STD-033D and provides bake temperatures of 104, 194 and 257°F (40, 90 and 125°C). A dry cabinet will simply pause the floor


life clock for a given reel or tray of compo- nents. Once a component has exceeded its floor life exposure time, there is no schedule for how long it would take for it to be reset in a dry (less than 5 percent RH) environment. While it is true that the standard has a


provision for resetting components with a dry cabinet after short exposure times, it necessi- tates placing them in the dry environment for five or ten times the length of the short-term exposure. This means that storing the parts


overnight in a dry cabinet after a day on the floor will not reset them for use the following day. For example, an MSL 2, 2a or 3 component that spends eight hours on the floor would require 40 hours in a dry cabinet to reset. An MSL 4, 5 and 5a component with eight


hours of exposure time would require 80 hours in a dry cabinet to reset. This is the only way a dry cab- inet can be used to “re-dry” components, provided the exposure times are short. This adds to the intricacy of dry storage logistics and often con- tributes to the impulse to bake everything.


Baking Drawbacks Baking, however, can permanently damage


the plastic tape and reels, carriers, carrier tape, tubes, and trays used to dispense the components. Damage to packaging materials can occur at tem- peratures as low as 113°F (45°C), making it impos- sible for placement machines to process these parts. Baking also exacerbates oxidization on the


MSD’s solder terminations, which is one of the largest contributors to soldering defects. Baking also takes a long time. It can take a long as 79 days for


SmartDRY SD-10 component dry storage cabinet. Baking also wastes a lot of energy. Baking


consumes 20 times the energy versus simply keep- ing the parts dry. And, since MSDs do not require baking unless they are MSL 6 or if the floor life was mistakenly exceeded, it would be more reliable and economical to keep the parts dry rather than bake them. Baking is commonly seen as a cure-all for


multiple soldering problems. This is not the case. There are many required thermal processes in the component manufacturing process. Most compo- nents should not require any additional baking from the time they are removed from the manufac- turer’s moisture barrier bag (MBB) and soldered. There are only two reasons that MSDs


should require baking after removal from the MBB — if the part is rated MSL 6 or if it has exceeded its floor life.


Dry Storage Recovery Many operations bake components out at


scale, due to the belief that dry storage cabinets


ost electronics professionals are well aware of the importance of ensuring com- ponents are dry before soldering. There


0.08 to 0.2 in. (2 to 4.5 mm) components at the pack- age-safe low temperature of 104°F (40°C) to as little as three hours at a package-melting temperature of 257°F (125°C) for MSL 2 MSDs, with exposure time past the expired floor life less than 72 hours. The higher the temperature, the shorter the


bake time. But, unless components can be unpack- aged, baked at a very high temperature and then repackaged, 104°F (40°C) is a safer option. If this safer temperature must be used, bake times can range from 5 to 79 days.


cannot perform to meet the parts accessibility demands of the manufacturing floor, while also complying with J-STD-033D. Frequent changeovers require ongoing access


to the dry cabinet, so the recovery performance of the cabinet becomes a factor. For example, consid- er an MSL 5 component (48-hour floor life) that has already been exposed for a day and needs to be stored for a week until the next changeover when it can be used. Is there a concern about additional exposure as the manufacturing team opens the cabi- net frequently for other parts? This exposure could potentially reduce its floor life clock even if the part is just sitting in the cabinet while recovering. Many desiccant dry storage cabinet


models are programmed to regenerate on a fixed timer and have recovery times that take 20, 30 and even 45 minutes to an hour to reach less than five percent RH after a door opening. This contributes to the perception that


dry cabinets are only useful for long-term storage. However, these recovery rates have improved in recent years as dry storage man- ufacturers innovate to meet the demands of the standards and modern EMS facilities. One cabinet used for this evaluation,


the ECD SmartDRY™ SD-10SB, recovered to less than five percent in under three min- utes (following a half-minute door open in a 50 percent RH, 77°F [25°C] ambient room). Assume this cabinet is on the manufac-


turing floor and is being accessed a dozen times per day. In this example, the MSL 5


part that needs to be stored for a week would incur only 4.2 hours of additional exposure time over the course of the week, while a cabinet with a 20- minute recovery time would expose the part over an additional 28 hours. Simply placing parts in a dry cabinet is not


going to reset a component’s floor life clock. In addition, baking everything just to be on the safe side is not necessarily the most effective route and can reduce component solderability, as well as con- tribute to other manufacturing issues. Improved performance of modern dry storage


cabinets as it relates to conforming to J-STD-033 establishes their importance for optimizing drying and baking protocols in manufacturing operations. As a result, manufacturers can better conform to the standard, maintain the best interests of customers


and preserve the reliability of the final product. Contact: ECD, 4287-B SE International Way,


Milwaukie, OR 97222 % 503-659-6100 E-mail: bob.schnyder@ecd.com Web: www.ecd.com r


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