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Guidelines for Handling and Processing Moisture
Sensitive Surface Mount Devices (SMDs)
internal moisture concentration reaches an equilibrium withthe ambient relative humidity. Thus the higher the relative
Certain plastic encapsulated surface mount devices (SMDs)
humidity, the greater the amount of absorbed moisture within
if not handled properly can incur damage during the solder
reflow attachment process to printed circuit boards (PCBs).
The damage occurs as a result of internal package cracking(commonly referred to as popcorn cracking) and / ordelamination between internal package interfaces (i.e., diesurface and mold compound). Such internal damage canlead to a number of possible failure modes including brokenbond wires and lifted ball bonds. If they reach the exterior of
the package they may provide an entry pathway for externalcontaminants. Furthermore, separations in the die attachregion can lead to increased electrical and thermalresistances, which may affect device performance in certainpackage styles where such a conduction path is required.
The root cause of this type of failure mechanism is the rapid
heating of the moisture absorbed within the plastic
encapsulant. All plastic packages absorb moisture. Duringtypical solder reflow operations when SMDs are mountedonto a PCB, the entire PCB and device population are
exposed to a rapid change in ambient temperature. Anyabsorbed moisture is quickly turned into superheated steam.
This sudden change in vapor pressure can cause the
FIGURE 1. CROSS SECTIONAL VIEW OF A MOISTURE
package to swell. If the pressure exerted exceeds the
SENSITIVE PLASTIC PACKAGE UNDERGOING
SOLDER REFLOW. ABSORBED MOISTURE
flexural strength of the plastic mold compound, then it is
TURNS TO VAPOR, WHICH CAUSES THE
possible to crack the package (see Figure 1). Even if the
PACKAGE TO SWELL.
package does not crack, interfacial delamination can occur.
A number of factors can influence the moisture sensitivity of
As mentioned earlier, the profile of the solder reflow process,
a package. These include both the internal dimensions and
which includes preheat, ramp up and maximum temperature
design of the lead frame, the external dimension of the
exposure, also affect the moisture sensitivity of an SMD (see
package and the physical properties of the die attach
Tech Brief TB334, Guidelines for Soldering Surface Mount
material and mold compound. Also, the die dimensions and
Components to PC Boards). In general, the slower the ramp
even the type of passivation can affect moisture sensitivity.
rate and the lower the maximum temperature, the less the
The last two factors which can influence the moisture
probability of potential damage due to moisture sensitivity.
sensitivity of a SMD are the amount of absorbed moistureand the solder reflow temperature profile. For any given
Moisture Sensitivity Classification
moisture sensitive SMD, once assembled, it is only the latter
In order to establish common criteria for the classification of
two factors that a PCB manufacturer has control over.
moisture sensitive SMD packages several industry
The amount of moisture absorbed within a plastic package is
specification were drafted. The more widely accepted
includes JEDEC STD22B, Test Method A112-A andIPC-SM-786A. These have recently been combined into
• Physical properties of the mold compound
IPC/JEDEC J-STD-020A (Moisture/Reflow Sensitivity
Classification for Plastic Integrated Circuit Surface Mount
• Relative humidity of the ambient atmosphere and,
Devices). These specifications outline the test methods toclassify the moisture sensitivity of a given SMD to one of
eight different levels (see Table 1).
The diffusion rate of moisture into the mold compound istemperature dependent. The higher the temperature, thefaster the surrounding moisture will penetrate the moldcompound. The absorption process will continue until the
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Technical Brief 363
TABLE 1. MOISTURE SENSITIVITY LEVELS
may be used. The solder reflow must be accomplishedwithin the specified floor life shown on the warning label.
Failure to do so may result in damage to the product.
Unused product can be stored in a cabinet with a controlled
ambient ≤ 20% RH when not in use. When product is
returned to production any previous floor exposure shall bededucted from the floor life indicated on the warning label.
When a variety of moisture sensitive SMDs are being used,
it is extremely important to maintain the sensitivity level and
total floor life exposure of each device. The floor life shownon the label is for a maximum factory ambient of 30oC / 60%
RH. Derating calculations have been published for use of
moisture sensitive SMDs in other temperature / humidity
As mentioned before, the ramp rates and maximum
1. Time after removing from dry pack in a ≤ 30oC / 60% RH ambient.
temperatures have a direct effect on moisture sensitivity.
2. Dry pack not required. Maximum conditions 30oC / 85% RH.
Moisture sensitivity classification is performed at a maximumtemperature of either 219oC/225oC or 235oC/240oC
The classification test procedure involves a specified soak
depending on the package dimensions. Higher reflow
duration at the stated floor life conditions for levels 3 through
temperatures may increase the moisture sensitivity of a
6. Accelerated conditions are used for level 1 and 2.
particular device type because of the associated increase in
Following the humidity soak, the packages are subjected to
the vapor pressure of the steam. Other precautions should
3 reflow cycles with either vapor phase or IR reflow. The
be observed in instances where reflow is being performed
specified maximum reflow temperatures are 219oC/225oC
with radiant heating, such as with IR reflow. Heating is not
or 235oC/240oC depending on package dimensions (refer to
uniform across the PCB. Outer edges of the board tend to
J-STD-020A). The product is then subjected to electrical
get hotter. Also smaller packages with less thermal mass
test, visual inspection, cross-sectioning and/or inspection
can achieve higher temperatures than larger packages in a
with acoustical microscopy. The package is assigned to the
mixed PCB design. Profiling of IR reflow systems should be
lowest level of moisture sensitivity for which it passes.
performed to account for these differences.
Several manufacturers employ wave solder for solderingSMDs to PCBs. Typically such soldering is performed at
If a particular package style is determined to be moisture
260oC. This method and temperature range is not
sensitive (levels 2 through 6), then the product must be
recognized by the IPC/JEDEC J-STD-020A and as such
shipped in dry pack. The dry pack bag is a tough, moisture
SMD packages have not been characterized for moisture
resistant bag. The moisture sensitive product is typically
sensitivity under these conditions. If a user is employing
baked for 24 hours at 125oC. Following the bake the product
this method, they should check with Intersil prior to use.
is placed inside a dry pack bag along with predeterminedamount of desiccant and a humidity sensitive indicator card.
The bag is then sealed. A moisture sensitivity warning labelis then affixed to the bag. The label will indicate the floor life
If a rework of a PCB with moisture sensitive SMDs is
after the bag is opened as well as the date the dry bag was
required, special precautions must be observed. Should the
sealed. The label will also contain information on storage
rework require complete exposure of the PCB to reflow
conditions, then the manufacturer needs to take into accountthe shortest floor life of any moisture sensitive SMD on the
board. If the floor life has been surpassed, then the entireboard should be re-baked.
Upon opening a dry pack bag with product, the user needsto check 2 items:
Localized board repair with a soldering iron or hot bar shouldnot damage neighboring packages. Care should be
exercised not to overheat individual leads of the replacement
• the moisture indicator from within the bag.
device. If a hot air gun is used for making board repairs, care
If the bag seal date is over 1 year and / or the humidity
should be taken to shield any surrounding moisture sensitive
indicator card shows >20% RH, the product needs to be
packages. If a moisture sensitive SMD is to be replaced, the
re-baked prior to reflow. If both the seal date and humidity
new device should be within its floor life. Any special
indicator card are within the requirements, then the product
requirements, which might be on the product’s data sheet,should be followed.
Technical Brief 363
Re-Baking of Moisture Sensitive Product
Moisture sensitive product which has been exposed to the
Dry packed product should be turned on a First In/First Out
factory ambient past its intended floor life or when the dry
(FIFO) basis to insure dry pack does not go beyond its
pack bag has been opened and the humidity indicator card
one-year expiration date. Preferably factory dry pack should
shows >20% RH needs to be baked dry again before
not be opened. If, however, an order requires opening a dry
reflowing. The baking process for dry packing is 24 hours at
pack bag for part of its content, the bag should be resealed
125oC. Shipping trays can typically withstand this
immediately and the removed contents transferred to a new
temperature (check with product supplier to be sure).
bag. The new dry pack bag shall meet Class I barrier
However, shipping tubes and tape and reel cannot. Two
requirements per Federal Test Method Standard 101,
Method 3030. Resealing of the new dry pack should occurwithin 30 minutes maximum and should follow the
1. For product in plastic tubes the product can be transferred
requirements of EIA-583 (Packaging Material Standards for
to metal tubes or placed on metal trays for the normal125oC bake out procedure. ESD precautions need to be
Moisture Sensitive Items) and / or IPC/JEDEC J-STD-033
(Standard for Handling, Packing, Shipping and Use ofMoisture/Reflow Sensitive Surface Mount Devices). A
2. Tubes and tape and reel can also be baked at 40oC
+5oC/-0oC at <5% RH for 192 hours or longer.
duplicate of the same moisture sensitive warning label as onthe original dry pack bag shall be affixed to the new bag. If
Following the bake out procedure the product needs to be
the product is exposed for greater than 30 minutes,
processed through reflow within its assigned floor life or it
can be returned to a storage cabinet with < 20% RH for useat a later time. In the case of extremely moisture sensitive
components (level 6) it is advisable to process throughreflow immediately after the bake.
 “Diffusion Model to Derate Moisture Sensitive Surface
Mount ICs for Factory Use Conditions”
, R. L. Shook andT.R. Conrad, Proc. 45th Electronic Components andTechnology Conference, pp. 440-449, 1995
All Intersil semiconductor products are manufactured, assembled and tested under ISO9000
quality systems certification.
Intersil semiconductor products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design and/or specifications at any time with-out notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate andreliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may resultfrom its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
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