PCB Design Surface Mount Guidelines for LGA - Digikey

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Contents
Recommended PCB Design & Surface Mount Guidelines
for Picor Corporation’s LGA Packages
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1
Receiving PCB Footprint. . . . . . . . . . . . . . . . . . . . . . Page 1
Stencil Designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2
Copper Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2
IPC/JEDEC Reflow Guidelines . . . . . . . . . . . . . . . . . . Page 2
LGA SIP Rework Guidelines . . . . . . . . . . . . . . . . . . . Page 3
Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 – 5
Introduction
Picor’s LGA (Land Grid Array) products are high performance,
high density solutions suitable for a variety of power
applications. The LGA is designed with minimal internal stray
parasitic elements, to improve electrical efficiency and
dynamic performance and has extremely low thermal
resistance to allow for optimal heat transfer from the internal
semiconductor junction to the leads of the package. In order
to harness the full value of Picor’s LGA solutions from a
system perspective it is important to follow a few simple
guidelines, as explained in this application note, regarding
PCB layout and surface mount techniques.
Receiving PCB Footprint
Figure 1 illustrates a typical 5 x 7 mm LGA layout with its
external components. The smaller pads along the right half of
the LGA are the input and output connections, along with the
power and ground connections. These receiving pads are
copper defined as shown in Figure 2. The recommended
receiving pads are 0.05mm longer on the “sides” and the
“heel”, and 0.2mm longer in the “toe” than the package
pad. 1 This allows for a proper solder fillet during re-flow.
The solder-mask is expanded by 0.025mm around the pad
edges (copper defined pads). The yellow box around the LGA,
as shown in Figure 1, is an optional keep-out border that
allows a hot-air re-working nozzle to reach the LGA
unobstructed.
Figure 1 – Typical 5 x 7 mm LGA receptor PCB layout with
a keep-out border for re-working.
The larger pads on the LGA, shown on the left side in Figure
1, are the power connections. The receptor pattern for these
pads should be solder-mask defined. The dimensions shown in
Figure 3 are the finished solder mask opening dimensions, as
they relate to the example in Figure 1. The dimensions shown
in Figure 4 are for use when a power pad is not located along
the edge of the LGA, but is located completely underneath
the body of the LGA. Over-etching of the solder mask could
cause a solder mask breakout to occur in areas where the
solder mask is the thinnest, which in turn may cause solder to
be leeched away from an adjoining pad. Check with the PCB
vendor for their recommended minimum solder mask feature.
0.20 mm (0.008”)
0.025 mm (0.001”)
Receiving Pad
TOE
Soldermask
Opening
X
LGA
I/O Pad
0.05 mm (0.002”)
0.025 mm (0.001”)
0.025 mm (0.001”)
0.05 mm (0.002”)
HEEL
0.025 mm (0.001”)
Y
0.05 mm (0.002”)
Figure 2 – Details of the copper defined I/O receiving pads and
solder-mask openings.
1
The terms heel, toe and side are typically used to describe the 4 sides of a
metal lead that mates with a pcb substrate. The heel being the edge that is
under the body of the component, the toe the side that extends beyond the
body of the component and the sides the edges that connect the heel and toe.
Recommended PCB Design & Surface Mount Guidelines
Picor Corporation • www.picorpower.com
for Picor Corporation’s LGA Packages Rev. 1.0 Page 1 of 6

The values for X and Y, shown in Figures 2, 3 and 4, are the
LGA pad dimensions and can be found at the end of this
guide or in the corresponding Picor LGA product data sheet.
0.20 mm (0.008”)
0.025 mm (0.001”)
TOE
X
LGA
Edge
Power Pad
0.025 mm (0.001”)
HEEL
Copper Pattern
When designing a board using Picor’s LGA package, it is very
important to make allowances for copper filled board area
around the power pads. The power pads of the LGA should
be connected directly to the polygon with solid connections
on all sides, not with thermal relief pads. The greater the area
of copper connected to the power pads of the LGA, the
better the thermal performance of the LGA package. If there
are internal layers available, then it is recommended that at a
minimum, the copper area of the top layer be mirrored on
inner layers with as many vias, on either side of the receiving
pads, as can be reliably manufactured. The vias in Figure 5 are
10mil holes with a 5mil annular ring and should be tented top
and bottom with solder mask.
Y
Soldermask
Opening
0.025 mm (0.001”)
Figure 3 – Solder-mask defined LGA edge power pads.
0.025 mm (0.001”)
X
0.025 mm (0.001”)
Figure 5 – Recommended blind and through-hole Via
Construction (dimensions shown are minimum values).
Soldermask
Opening
LGA
Internal
Power Pad
Figure 4 – Solder-mask defined LGA internal power pads.
0.025 mm (0.001”)
Y
0.025 mm (0.001”)
The downside of large areas of copper is the amount of heat
required to reflow the power pads of the LGA. If the reflow
zone’s temperature has to be greatly increased to reflow the
LGA, then components mounted on smaller areas of copper
could be thermally damaged. We recommend that routine
reflow temperature profiling should be completed before
assembling with a new PCB design to determine peak device
temperatures during the SMT process.
IPC/JEDEC Reflow Guidelines
Stencil Design
Picor recommends a 6mil thick stencil, with stencil openings
of 80% of the receiving pad area. For solder mask defined
openings, the receiving area is the same area as the solder
mask opening.
The 5 x 7 mm LGA package is designed to be re-flowed using
lead-free solder, with a maximum reflow temperature of
260°C for 20 to 40 seconds. The package can be maintained at
a temperature above 217°C for 60 to 150 seconds.
The reflow profile should adhere to the JEDEC standard,
taken from IPC/JEDEC J-STD-020C July, 2004, shown in Figures
6 and 7. Figure 7 is a lead-free reflow profile, but the 5 x 7
mm LGA package is compatible with leaded solders as well.
Recommended PCB Design & Surface Mount Guidelines
Picor Corporation • www.picorpower.com
for Picor Corporation’s LGA Packages Rev. 1.0 Page 2 of 6

T P
tp
Critical Zone
Ramp-up
T L
to T P
T L
Temperature
Ts max
Ts min
ts
Preheat
t L
Ramp-down
25
t 25°C to Peak
Time
Figure 6 –– IPC/JEDEC Classification Reflow Profile.
Profile Feature
Pb-Free Assembly
Average Ramp-Up Rate
(TS MAX to T P )
3 °C / second max.
Preheat
– Temperature Min (Ts MIN ) 150 °C
– Temperature Max (Ts MAX ) 200 °C
– Time (ts MIN to ts MAX ) 60 – 180 seconds
Time maintained above
– Temperature (T L ) 217 °C
–Time(t L )
60 – 150 seconds
Peak/Classification Temperature (T P ) 260 °C +0/-5 °C
Time within 5 °C
20 – 40 seconds
of actual Peak Temperature (t P )
Ramp-Down Rate
Time 25 °C to Peak Temperature
6 °C / second max.
8 minutes max.
NOTE: All temperatures refer to topside of the package measured in
the package body surface"
LGA Rework Guidelines
The 5 x 7 mm LGA package is capable of being re-worked in a
non-destructive manner using standard hot-air reworking
stations. Care must be taken that the temperature the
package is exposed to does not exceed the maximum reflow
temperature of 260°C. Pre-heating of the board can be done
to minimize the time the peak re-work temperature is
applied. Also, solder flux should be applied to the area to
insure proper solder reflow.
Figure 7 –– IPC/JEDEC Reflow Profiles table.
Recommended PCB Design & Surface Mount Guidelines
Picor Corporation • www.picorpower.com
for Picor Corporation’s LGA Packages Rev. 1.0 Page 3 of 6

Picor 5 x 7 mm LGA Packages:
Picor’s 5 x 7 mm LGA package is based on an industry standard 0.8mm pitch MLCC package.
PIN 1
5.00mm ±0.03mm
0.45mm ±0.05mm
1.20mm
3.20mm
2.40mm
17
1 2
3
B
7.00mm ±0.03mm
PI2xxx
YYWW
0.80mm
0.00mm
0.80mm
2.00mm
2.80mm
13
12
8
7
A
2.00mm ±0.06mm
0.80mm
0.30mm ±0.05mm
0.40mm ±0.05mm
0.40mm ±0.05mm
A: I/O Pads (Pins 6 - 14)
Copper Defined
1.20mm ±0.05mm
B: Power Pads (Pins 1 - 5, 15 - 17)
Soldermask Defined
0.89mm 1.60mm 0.80mm 0.80mm 1.20mm 0.80mm 0.53mm
1.09mm
0.73mm
Pin 1
0.80mm
1.20mm
0.80mm
1.20mm
Notes:
SM = Solder mask defined
Pad = Copper defined
All dimensions are finished values.
Drawing is "top view" perspective.
0.80mm
0.80mm
SM 0.63mm
PAD 0.55mm
SM 1.25mm
SM 0.55mm
PAD 0.50mm
SM 0.60mm
Figure 8 –– 5 x 7 mm, 17 Lead Package. (PI2121, PI2123, PI2125)
Recommended PCB Design & Surface Mount Guidelines
Picor Corporation • www.picorpower.com
for Picor Corporation’s LGA Packages Rev. 1.0 Page 4 of 6

5.00mm ±0.03mm
PIN 1
0.45mm ±0.05mm
3.20mm
2.40mm
C
17
1.20mm
1 2
3
B
7.00mm ±0.03mm
PI2xxx
YYWW
0.80mm
0.00mm
0.80mm
2.00mm
2.80mm
13
12
8
7
A
2.00mm ±0.06mm
0.80mm
0.30mm ±0.05mm
0.40mm ±0.05mm
1.20mm ±0.05mm
0.40mm ±0.05mm
A: I/O Pads (Pins 6 - 14)
Copper Defined
1.20mm ±0.05mm
B: Power Pads (Pins 1 - 5, 15 - 17)
Soldermask Defined
0.50mm ±0.05mm
C: Internal Power Pads
Soldermask Defined (8 Places)
0.89mm
1.60mm
0.80mm
0.80mm
0.80mm
1.20mm
0.53mm
1.09mm
0.73mm
Pin 1
0.80mm
1.20mm
1.20mm
Notes:
SM = Solder mask defined
Pad = Copper defined
All dimensions are finished values.
Drawing is "top view" perspective.
SM 0.55mm
0.80mm
0.80mm
SM 1.25mm
0.80mm
SM 0.63mm
PAD 0.55mm
SM 1.25mm
Figure 9 –– 5 x 7 mm, 25 Lead Package. (PI2122)
SM 0.55mm
PAD 0.50mm
SM 0.60mm
Recommended PCB Design & Surface Mount Guidelines
Picor Corporation • www.picorpower.com
for Picor Corporation’s LGA Packages Rev. 1.0 Page 5 of 6

Vicor’s comprehensive line of power solutions includes high-density AC-DC &
DC-DC modules and accessory components, fully configurable AC-DC & DC-DC
power supplies, and complete custom power systems.
Information furnished by Vicor is believed to be accurate and reliable. However, no responsibility
is assumed by Vicor for its use. No license is granted by implication or otherwise under any patent
or patent rights of Vicor. Vicor components are not designed to be used in applications, such as
life support systems, wherein a failure or malfunction could result in injury or death. All sales are
subject to Vicor’s Terms and Conditions of Sale, which are available upon request.
Specifications are subject to change without notice.
Recommended PCB Design & Surface Mount Guidelines
Picor Corporation • www.picorpower.com
for Picor Corporation’s LGA Packages Rev. 1.0 Page 6 of 6 7/08