AN1850 Freescale Semiconductor / Motorola, AN1850 Datasheet - Page 6

• Manufacturer Part Number: AN1850
• Description: Flip-Chip PBGA Package Construction Assembly and Board-Level Reliability
• Manufacturer: Freescale Semiconductor / Motorola

1.3 Surface Mount Assembly
The board assembly process for FC PBGA is basically the same as for CBGA with a couple of exceptions.
Due to its high-Pb content solder ball, the CBGA has very speciÞc solder paste volume requirements while
the FC PBGA has none. The CBGAÕs minimum volume of 0.079 mm
with 0.84 mm diameter apertures. Another difference may be in the proÞling and zone settings of the reßow
furnace. The CBGA has a much higher thermal mass than the PBGA; therefore, it may be the coolest part
on a given assembly. Both part types should be proÞled along with other suspected low and high
temperature packages on the board. For the BGAs, this is accomplished by placing a thermocouple under
the part, preferably within the solder joint, surrounded by thermally conductive grease or epoxy.
The reßow proÞle for both package types should follow the recommendations of the solder paste supplier.
Neither package has a required reßow proÞle, and both packages are qualiÞed to a maximum reßow
temperature of 225¡C. In general, it is recommended that the proÞle have a preheat sufÞcient to raise
temperature of the joints to 100¡C over a period of no less than 50 seconds. Too long of a rise time can cause
the ßux or solder paste to dry out and reduce its effectiveness. The peak temperature on any component
should generally be between a minimum of 205¡C and a maximum 220¡C. It is recommended that the dwell
time be less than two minutes above 183¡C. The desirable dwell time above 183¡C is greater than 50
seconds and less than 80 seconds.
With regard to component placement using automated pick and place equipment, the solder balls on the two
BGA types are easily recognized by most vision systems. The solder ball diameter, grayness (due to the
different Pb content), and package body colors are different for FC PBGA and CBGA, so adjustments may
be necessary to certain vision parameters. Alignment can take place off of the solder balls or the package
body for either package type. It should be noted that due to JEDEC registrational differences, the body size
for a given pin count may be slightly different for FC PBGA versus CBGA. See the last line of Table 1 for
speciÞc information.
Surface Mount Assembly
6
Flip-Chip PBGA Package ConstructionÑ Assembly and Board-Level Reliability
Via
Figure 6. Recommended CBGA Motherboard Solder Pad Geometry.
Vi
a
Solder Pad
Cross Section
Solder Pad
0.30 mm (12 mil) finished plated through-hole
0.65 mm (25 mil) annular pad
0.30 + mm (12 + mil) wide line between pads
0.72 ± 0.037 mm (28 1/2 ± 1-1/2 mil)
0.076 ± .025 mm (3 ± 1 mil)
Clearance between copper pad and solder mask
Solder mask away from copper pad
PCB Laminate
Copper diameter
Liquid photoimageable solder mask
3
equates to a 0.15 mm thick stencil