www.superdry.info The Next Generation in Handling Moisture Sensitive Devices The influence of humidity on the reliability of electronic components is generally underestimated and often simply unknown. Moisture sensitive devices (MSDs) are electronic components encapsulated with plastic compounds and other organic materials. Moisture from atmospheric humidity enters these permeable packaging materials by diffusion and collects at the interfaces of dissimilar material. The moisture sensitivity of a particular package is influenced by different factors, including the internal dimensions and design of the lead frame, the external dimension of the package, and the physical properties of the die attach material and molding compound. How much moisture a particular package actually absorbs depends on factors such as temperature, the physical properties of the mold compound, the relative humidity of the ambient atmosphere, and how much time the component is exposed to those conditions. The diffusion rate of moisture into the mold compound is temperature‐dependent. The higher the temperature, the faster the surrounding moisture will penetrate the mold compound. The absorption process will continue until the internal moisture concentration reaches equilibrium with the ambient relative humidity. The higher the relative humidity, the greater the amount of absorbed moisture within the plastic package. Lower volume, higher mix production environments find themselves more at risk without proper handling procedures in place as well, as individual trays or reels of components take longer to empty and parts have more time to absorb moisture. The original IPC/JEDEC J‐STD‐033 was designed to address the problems associated with Moisture Sensitive Devices (MSD). The standard contains handling, packing, shipping and implementation recommendations and guidelines. In summation, the manufacturer of a moisture sensitive component must test and classify the device based upon a maximum floor life at 30 deg. C at 60% Relative Humidity (prior to reflow). The component is dry‐packed with proper identification prior to shipment to the assembler. Theoretically, once the dry bags are opened, the components must be assembled and reflowed within the specified time limits. Lead Free processing increases MSD problems dramatically With the introduction of lead free, the risks associated with marginal or improper handling of MSDs has increased dramatically. Higher reflow temperatures drive up the saturated vapor pressure to double or even triple that present in tin lead reflow processes. The higher temperature increases the water pressure inside the components, and as a result, the allowable moisture content and associated floor life have to be reduced. All moisture‐sensitive components have to be requalified by their manufacturers for lead‐free and they are typically downgraded by at least one and generally two levels of sensitivity. This significantly affects how components must be are handled, processed and stored. Suddenly, manufacturers that are currently handling MSL 2 or MSL 3 components are now looking at processing MSL 5 or MSL 6. The SMTA’s MSD Council is among the those who have reported that even passive components (ceramic chip resistors and capacitors), normally classified as MSL 1 ( unlimited floor life) have shown field failures after lead free reflow due to presence of moisture in the component. Another major impact of lead free reflow for assemblers is the handling and storage of PWBs, as the incidence of delamination has increased with the change in thermal processing. PWBs need to be treated as MSL classification 4, in other words processed within 72 hours of open shop floor time. Dry Solutions In the same way that electrostatic discharge (ESD) became an important focus of attention 10 years ago, the increasing rate of failures associated with moisture sensitivity today is requiring that manufacturers invest more time and energy in finding useful and cost effective solutions. Engineers have a variety of ways in which to combat moisture. Some methods address storage, in an attempt to “stop the clock” dictated by the respective MSL of the device. Beyond that are methods of drying, removing moisture that has been absorbed by the devices and in effect “turning back the clock.” “Baking” components is a standard method that has been employed for years and is in fact cited within IPC/JEDEC J‐STD‐033. This method is not without its drawbacks, however, particularly that of oxidation. Additionally taped components cannot be exposed to 125o C temperatures commonly used without destroying the tapes. And with more and more components and PWBs requiring special handing attention, a new shop floor materials logistics problem arises, with different baking times and temperatures. The results are often that components can be left in the ovens for hours at a time after baking. The result? In this ambient atmosphere moisture is once again being absorbed back into the components. A New Dry Cabinet Solution MSD handling specialist and global manufacturer Totech Super DryR introduced in 2008 an alternative that offers a solution to many of the technical drawbacks associated with baking, such as oxidation and intermetallic growth. But it also addresses the shop floor logistics problems as well. All Super DryR cabinets utilize Zeolite A which is proven to be the most effective desiccant available. Referred to also as “molecular sieves” these are desiccants with some differing properties to those of silica gel. They are synthetically produced, highly porous crystalline metalalumino silicates and possess many internal cavities that are linked by window openings of precise diameters. Totech has expanded upon their patented technology that incorporates Zeolite A and developed a new dry unit with unprecedented dehumidification performance properties. Dehumidification Capabilities of 1M3 Desiccant Cabinets The XSD Series The new XSD Series cabinet with the U 5000 dry unit that has been introduced can achieve <1% RH and can deliver to that set point from 50% ambient in less than 3 minutes. Additionally, the strength of the dehumidification delivered by the integrated drier system enables merely single digit loss and almost instant recovery after routine length door openings of 30 seconds But what is new for this MSD handling solution is not just the unprecedented 0.5% RH performance level. Designed with thermally insulated stainless steel and ESD glass construction, the XSD can provide an accelerated drying profile approaching the speed of traditional baking ovens. It incorporates a 65o C heating system that can deliver consistent temperature profiles throughout the entire cabinet. Oxidation has always been a very significant drawback of baking components, and in fact even a single bake cycle at recommended 125o temperatures will significantly increase wetting times. The Super Dry process dramatically reduces this oxidation risk, because it employs relatively low heat delivered within an exceptionally dry atmosphere. The oxygen molecules in water are much more of a catalyst to the oxidation process than those in the air. So heating at the sub 0.5% RH levels the XSD is capable of achieving does not promote the oxidation common to traditional processes. And furthermore, 65 degrees is safe for taped components, enabling drying of components on reels without damage to the tape. XSD 1404 Smooth Integration The Super DryR MSD handling solution extends the objectives of IPC/JEDEC J‐STD‐033 and offers an environmentally friendly, power saving alternative to traditional methods that can fit smoothly into existing assembly operations. Its combined ability to store and to dry components offers a convenient way in which to comprehensively address the significant risks caused by the absorption of moisture by components and PWBs. Reference Conditions for Drying Mounted or Unmounted SMD
Floor life begins counting at time =0 after drying
Packages that were exposed to Conditions <60% RH
(For ICs with Novolac, Biphenyl and Multifunctional Epoxies
Body
Thickness
Thickness
Drying at 1% RH
(HSD+XSD-Series)
Level
Drying at 2% RH
(SD+SDA-Series)
Drying at 5% RH
(N²-Cabinets)
according to IPC J-STD-033B
25°C
1% RH
40°C
1% RH
60°C
1% RH
25°C
2% RH
40°C
2% RH
40°C
5% RH
90°C
5% RH
2a
2 days
1 day
12 hours
5 days
2 days
5 days
23 hours
3
3 days
1 day
12 hours
8 days
3 days
8 days
33 hours
4
4 days
2 days
24 hours
9 days
4 days
9 days
37 hours
5
5 days
2 days
24 hours
10 days
5 days
10 days
41 hours
5a
6 days
2 days
24 hours
10 days
6 days
10 days
54 hours
2a
10 days
3 days
36 hours
22 days
10 days
22 days
3 days
3
11 days
3 days
36 hours
23 days
11 days
23 days
4 days
4
14 days
4 days
2 days
28 days
14 days
28 days
5 days
5
16 days
5 days
3 days
35 days
16 days
35 days
6 days
5a
18 days
5 days
3 days
56 days
18 days
56 days
8 days
2a
20 days
6 days
3 days
67 days
20 days
67 days
10 days
3
22 days
7 days
4 days
67 days
22 days
67 days
10 days
4
22 days
7 days
4 days
67 days
22 days
67 days
10 days
5
22 days
7 days
4 days
67 days
22 days
67 days
10 days
5a
22 days
7 days
4 days
67 days
22 days
67 days
10 days
≤1.4 mm
Thickness
>1.4 mm
≤2.0 mm
Thickness
>2.0 mm
4.5 mm