Application Note (continued)
V•I Chip soldering recommendations
V•I Chip modules are intended for reflow soldering processes. The
following information defines the processing conditions required for
successful attachment of a V•I Chip to a PCB. Failure to follow the
recommendations provided can result in aesthetic or functional failure
of the module.
V•I Chip modules are currently rated at MSL 5. Exposure to ambient
conditions for more than 72 hours requires a 24 hour bake at 125ºC to
remove moisture from the package.
Removal and rework
V•I Chip modules can be removed from PCBs using special tools such
as those made by Air-Vac. These tools heat a very localized region of
the board with a hot gas while applying a tensile force to the
component (using vacuum). Prior to component heating and removal,
the entire board should be heated to 80-100ºC to decrease the
component heating time as well as local PCB warping. If there are
adjacent moisture-sensitive components, a 125ºC bake should be used
prior to component removal to prevent popcorning. V•I Chip modules
should not be expected to survive a removal operation.
Solder paste stencil design
Solder paste is recommended for a number of reasons, including
overcoming minor solder sphere co-planarity issues as well as simpler
integration into overall SMD process.
63/37 SnPb, either no-clean or water-washable, solder paste should be
used. Pb-free development is underway.
The recommended stencil thickness is 6 mils. The apertures should be
20 mils in diameter for the Inboard (BGA) application and 0.9-0.9:1 for
the Onboard (J-Leaded).
Joint Temperature, 220ºC
Case Temperature, 208ºC
Pick and place
Inboard (BGA) modules should be placed as accurately as possible
to minimize any skewing of the solder joint; a maximum offset of
10 mils is allowable. Onboard (J-Leaded) modules should be placed
within ±5 mils.
To maintain placement position, the modules should not be subjected
to acceleration greater than 500 in/sec2 prior to reflow.
Figure 25—Thermal profile diagram
There are two temperatures critical to the reflow process; the solder
joint temperature and the module’s case temperature. The solder joint’s
temperature should reach at least 220ºC, with a time above liquidus
(183ºC) of ~30 seconds.
The module’s case temperature must not exceed 208 ºC at anytime
Because of the ∆T needed between the pin and the case, a forced-air
convection oven is preferred for reflow soldering. This reflow method
generally transfers heat from the PCB to the solder joint. The module’s
large mass also reduces its temperature rise. Care should be taken to
prevent smaller devices from excessive temperatures. Reflow of
modules onto a PCB using Air-Vac-type equipment is not recommended
due to the high temperature the module will experience.
For the BGA-version, a visual examination of the post-reflow solder
joints should show relatively columnar solder joints with no bridges. An
inspection using x-ray equipment can be done, but the module’s
materials may make imaging difficult.
The J-Lead versions solder joints should conform to IPC 12.2
• Properly wetted fillet must be evident.
• Heel fillet height must exceed lead thickness plus solder thickness.
Figure 26— Properly reflowed V•I Chip J-Lead
V•I Chip Voltage Transformation Module
Page 13 of 16