WAN_0118
w
Guidelines on How to Use QFN Packages and Create
Associated PCB Footprints
INTRODUCTION
The Quad Fine Pitch No Leads (QFN) package is a leadless plastic package, which obtains electrical
contact via lands on the bottom surface of the device. Its compact nature and low profile makes the
QFN package ideal for designs where space considerations are at a premium. This small size is one
of the main reasons why the QFN package is chosen for Wolfson Microelectronics devices for
portable applications.
In addition to the bottom surface mounted pins, the other distinguishing feature of this package type
is the exposed die paddle on the bottom side of the device. This paddle can be used to add extra
strength in PCB mounting and to conduct heat more efficiently away from the die. The paddle may in
future be bonded as a further analogue ground and so it is recommended that it be connected to the
analogue ground of the PCB it is mounted to. The Chip On Lead Quad Fine Pitch No Leads (COL
QFN) package has no paddle.
This Application note sets out to explain some of the issues related to the design of a PCB footprint
for the QFN package and then goes on to describe practical considerations when soldering the
device to a PCB.
PACKAGE DIMENSIONS
The first thing to consider when creating a QFN footprint is the package drawing for the device.
Wolfson uses a number of different QFN packages based on JEDEC specifications as follows:
SIZE
PIN
WOLFSON
TYPE
4MM×4MM
24
C
4MM×4MM
28
A AND C
5MM×5MM
28
A
5MM×5MM
32
A AND C
6MM×6MM
40
C
7MM×7MM
48
C
9MM×9MM
64
C
Figure 1 QFN Package Range
WOLFSON MICROELECTRONICS plc
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August 2006, Rev 2.2
Copyright ©2006 Wolfson Microelectronics plc
WAN_0118
The Wolfson QFN package currently has two types of lead termination features, these are as follows.
WOLFSON TYPE A
The Wolfson Type A package is based on the JEDEC MO-220 specification with a slight modification
on the pad design. In the Type A package there is mould compound round the bottom corner of the
package (see arrow). After reflow a solder fillet between the PCB and the side of the package is not
required; the side of the package is not required to be solderable. This is as defined in international
standard IPC-A-610D. Refer to extract in the Appendix.
Figure 2 Type A QFN Package
WOLFSON TYPE C
The Type C package is based on the JEDEC MO-220 specification with pads that are extended up
the side of the package. After reflow a solder fillet between the PCB and the side of the package is
not required; the side of the package is not required to be solderable. This is as defined in
international standard IPC-A-610D. Refer to extract in the Appendix.
Figure 3 Type C QFN Package
The package type is dependant on the types of the part supplied and product family and can be
found in the product data sheet. The dimension of the packages are, at time of document release,
as follows. Please refer to the individual datasheets for the most current issue of the package
dimensions.
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August 2006, Rev 2.2
2
WAN_0118
FL: 24 PIN QFN PLASTIC PACKAGE 4 X 4 X 0.9 mm BODY, 0.50 mm LEAD PITCH
DM035.C
DETAIL 1
D
D2
19
24
1
18
EXPOSED
GROUND 6
PADDLE
A
INDEX AREA
(D/2 X E/2)
4
E2
E
SEE DETAIL 2
13
6
2X
12
7
b
e
1
bbb M C A B
2X
aaa C
aaa C
TOP VIEW
BOTTOM VIEW
DETAIL 1
A
0.08 C
45
degrees
A1
SIDE VIEW
C
DETAIL 2
5
0.32mm
DETAIL 2
SEATING PLANE
L
L1
Datum
1
ccc C
A3
EXPOSED
GROUND
PADDLE
W
Terminal
tip
e/2
e
R
T
A3
G
H
b
Exposed lead
Half etch tie bar
DETAIL 2
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
H
L
L1
T
MIN
0.80
0
0.18
2.00
2.00
0.30
0.03
Dimensions (mm)
NOM
MAX
NOTE
0.90
1.00
0.02
0.05
0.20 REF
1
0.30
0.25
4.00
2.15
4.00
2.15
0.50 BSC
0.213
0.1
0.40
2.25
2
2.25
2
0.50
0.15
7
0.1
0.2
W
Tolerances of Form and Position
aaa
bbb
ccc
REF:
0.15
0.10
0.10
JEDEC, MO-220, VARIATION VGGD-2.
NOTES:
1. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. FALLS WITHIN JEDEC, MO-220, VARIATION VGGD-2.
3. ALL DIMENSIONS ARE IN MILLIMETRES.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JEDEC 95-1 SPP-002.
5. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
6. REFER TO APPLICATIONS NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
7. DEPENDING ON THE METHOD OF LEAD TERMINATION AT THE EDGE OF THE PACKAGE, PULL BACK (L1) MAY BE PRESENT.
8. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
Figure 4 24 pin 4x4 QFN Package Wolfson Type C
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August 2006, Rev 2.2
3
WAN_0118
DM043.D
FL: 28 PIN COL QFN PLASTIC PACKAGE 4 X 4 X 0.75 mm BODY, 0.45 mm LEAD PITCH
DETAIL 1
D
D2
28
22
21
1
INDEX AREA
(D/2 X E/2)
4
E2
A
E
SEE DETAIL 2
15
7
2X
8
14
1
bbb M C A B
b
e
2X
aaa C
aaa C
TOP VIEW
BOTTOM VIEW
DETAIL 1
A
0.08 C
A1
SIDE VIEW
C
5
PIN 1
IDENTIFICATION
0.150MM SQUARE
L
Datum
L1
0.275MM
DETAIL 2
SEATING PLANE
DETAIL 2
0.275MM
1
ccc C
A3
Terminal
tip
e/2
e
R
W
T
A3
H
G
b
Exposed lead
DETAIL 2
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
H
L
L1
T
W
MIN
0.725
0
0.18
3.95
3.95
Dimensions (mm)
NOM
MAX
NOTE
0.75
0.775
0.02
0.05
0.203 REF
1
0.23
0.28
4.00
2.70 REF
4.00
2.70 REF
0.45 BSC
0.535 REF
0.100 REF
0.40 REF
0.05 REF
0.100 REF
0.230 REF
4.05
2
4.05
2
7
Tolerances of Form and Position
aaa
bbb
ccc
REF:
0.15
0.10
0.10
JEDEC, MO-220
NOTES:
1. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. FALLS WITHIN JEDEC, MO-220, VARIATION VGGD-2.
3. ALL DIMENSIONS ARE IN MILLIMETRES.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JEDEC 95-1 SPP-002.
5. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
6. REFER TO APPLICATIONS NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
7. DEPENDING ON THE METHOD OF LEAD TERMINATION AT THE EDGE OF THE PACKAGE, PULL BACK (L1) MAY BE PRESENT.
8. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
Figure 5 28 pin 4x4 COL QFN Package Wolfson Type A
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August 2006, Rev 2.2
4
WAN_0118
FL: 28 PIN QFN PLASTIC PACKAGE 4 X 4 X 0.75 mm BODY, 0.45 mm LEAD PITCH
DM042.B
DETAIL 1
D
D2
28
22
21
1
EXPOSED
GROUND 6
PADDLE
A
INDEX AREA
(D/2 X E/2)
4
E2
E
SEE DETAIL 2
15
7
0.226 Ref.
2X
8
14
b
e
1
bbb M C A B
2X
aaa C
aaa C
TOP VIEW
BOTTOM VIEW
DETAIL 1
A
0.08 C
45
degrees
A1
SIDE VIEW
C
DETAIL 2
DETAIL 2
SEATING PLANE
Datum
0.30mm
EXPOSED
GROUND
PADDLE
A3
L
5
1
ccc C
A3
Terminal
tip
e/2
e
R
G
b
Exposed lead
DETAIL 2
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
L
aaa
bbb
ccc
REF:
MIN
0.70
0
0.175
3.95
2.55
3.95
2.55
0.375
Dimensions (mm)
NOM
MAX
NOTE
0.75
0.80
0.02
0.05
0.203 REF
1
0.185
0.18
4.00
4.05
2.6
2.65
2
4.05
4.00
2
2.6
2.65
0.45 BSC
0.560
0.425
0.475
Tolerances of Form and Position
0.15
0.10
0.10
JEDEC, MO-220
NOTES:
1. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. FALLS WITHIN JEDEC, MO-220.
3. ALL DIMENSIONS ARE IN MILLIMETRES.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JEDEC 95-1 SPP-002.
5. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
6. REFER TO APPLICATIONS NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
7. DEPENDING ON THE METHOD OF LEAD TERMINATION AT THE EDGE OF THE PACKAGE, PULL BACK (L1) MAY BE PRESENT.
8. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
Figure 6 28 pin 4x4 QFN Package Wolfson Type C
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August 2006, Rev 2.2
5
WAN_0118
FL: 28 PIN QFN PLASTIC PACKAGE 5 X 5 X 0.9 mm BODY, 0.50 mm LEAD PITCH
CORNER
TIE BAR
5
SEE DETAIL A
D2
B
D2/2
27
22
DM023.G
D
28
INDEX AREA
(D/2 X E/2)
L
21
1
EXPOSED
GROUND 6
PADDLE
2
E2/2
A
A
15
E2
E
7
SEE DETAIL B
14
8
13
aaa C
2X
b
ccc M C A B
B
e
aaa C
2X
BOTTOM VIEW
TOP VIEW
DETAIL A
ccc C
DETAIL B
0.210mm
0.
56
6
m
m
EXPOSED
GROUND
PADDLE
R
e
L
A1
1
e/2 TERMINAL TIP
SIDE VIEW
CORNER
TIE BAR
5
0.
15
28x b
bbb M C A B
0.08 C
SEATING PLANE
DATUM
C
1
A
28x K
(A3)
1
0.3
8m
m
Symbols
A
A1
A3
b
D
D2
E
E2
e
L
L1
R
K
aaa
bbb
ccc
REF:
MIN
0.85
0
0.18
3.2
3.2
0.35
Dimensions (mm)
NOM
MAX
0.90
1.00
0.02
0.05
0.2 REF
0.23
0.30
5.00 BSC
3.3
3.4
5.00 BSC
3.3
3.4
0.5 BSC
0.4
0.45
0.1
1
L1
R
L1
NOTE
1
2
2
1
b(min)/2
0.20
Tolerances of Form and Position
0.15
0.10
0.10
JEDEC, MO-220, VARIATION VHHD-1
NOTES:
1. DIMENSION b APPLIED TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. DIMENSION L1 REPRESENTS TERMINAL PULL BACK FROM
PACKAGE SIDE WALL. MAXIMUM OF 0.1mm IS ACCEPTABLE. WHERE TERMINAL PULL BACK EXISTS, ONLY UPPER HALF OF LEAD IS VISIBLE ON PACKAGE SIDE WALL DUE TO HALF
ETCHING OF LEADFRAME.
2. FALLS WITHIN JEDEC, MO-220 WITH THE EXCEPTION OF D2, E2:
D2,E2: LARGER PAD SIZE CHOSEN WHICH IS JUST OUTSIDE JEDEC SPECIFICATION
3. ALL DIMENSIONS ARE IN MILLIMETRES
4. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
5. SHAPE AND SIZE OF CORNER TIE BAR MAY VARY WITH PACKAGE TERMINAL COUNT. CORNER TIE BAR IS CONNECTED TO EXPOSED PAD INTERNALLY
6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
Figure 7 28 pin 5x5 QFN Package Wolfson Type A
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August 2006, Rev 2.2
6
WAN_0118
FL: 32 PIN QFN PLASTIC PACKAGE 5 X 5 X 0.9 mm BODY, 0.50 mm LEAD PITCH
CORNER
TIE BAR
5
SEE DETAIL A
D2
B
D2/2
25
DM030.E
D
32
L
1
24
INDEX AREA
(D/2 X E/2)
EXPOSED
GROUND 6
PADDLE
E2/2
A
E2
17
E
SEE DETAIL B
8
16
aaa C
2X
15
9
b
2X
B
e
aaa C
TOP VIEW
BOTTOM VIEW
DETAIL A
ccc C
(A3)
1
1
0.08 C
SEATING PLANE
SIDE VIEW
CORNER
TIE BAR
5
32x b
bbb M C A B
A1
L
C
A
0.4
1
e/2 TERMINAL TIP
m
m
0.
56
1
e
L1
0.35
L1
R
aaa
bbb
ccc
REF:
0.18
4.90
3.2
4.90
3.2
EXPOSED
GROUND
PADDLE
R
A
A1
A3
b
D
D2
E
E2
e
L
L1
R
K
MIN
0.85
0
m
Symbols
m
32x K
6
DATUM
3
DETAIL B
Dimensions (mm)
NOM
MAX
0.90
1.00
0.02
0.05
0.2 REF
0.23
0.30
5.00
5.10
3.3
3.4
5.00
5.10
3.3
3.4
0.5 BSC
0.4
0.45
0.1
NOTE
1
2
2
1
b(min)/2
0.20
Tolerances of Form and Position
0.15
0.10
0.10
JEDEC, MO-220, VARIATION VHHD-2
NOTES:
1. DIMENSION b APPLIED TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. DIMENSION L1 REPRESENTS TERMINAL PULL BACK FROM
PACKAGE SIDE WALL. MAXIMUM OF 0.1mm IS ACCEPTABLE. WHERE TERMINAL PULL BACK EXISTS, ONLY UPPER HALF OF LEAD IS VISIBLE ON PACKAGE SIDE WALL DUE TO HALF
ETCHING OF LEADFRAME.
2. FALLS WITHIN JEDEC, MO-220 WITH THE EXCEPTION OF D2, E2:
D2,E2: LARGER PAD SIZE CHOSEN WHICH IS JUST OUTSIDE JEDEC SPECIFICATION
3. ALL DIMENSIONS ARE IN MILLIMETRES
4. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
5. SHAPE AND SIZE OF CORNER TIE BAR MAY VARY WITH PACKAGE TERMINAL COUNT. CORNER TIE BAR IS CONNECTED TO EXPOSED PAD INTERNALLY.
6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
Figure 8 32 pin 5x5 QFN Package Wolfson Type A
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August 2006, Rev 2.2
7
WAN_0118
FL: 32 PIN QFN PLASTIC PACKAGE 5 X 5 X 0.9 mm BODY, 0.50 mm LEAD PITCH
DM033.D
D
DETAIL 1
D2
32
25
L
1
24
4
EXPOSED
GROUND 6
PADDLE
A
INDEX AREA
(D/2 X E/2)
E2
17
E
8
16
2X
15
9
b
B
e
1
bbb M C A B
2X
aaa C
aaa C
TOP VIEW
BOTTOM VIEW
ccc C
A3
A
5
0.08 C
C
SEATING PLANE
R = 0.3MM
A1
SIDE VIEW
EXPOSED
GROUND
PADDLE
DETAIL 2
W
T
A3
b
Exposed lead
DETAIL 1
G
H
Half etch tie bar
DETAIL 2
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
H
L
T
W
MIN
0.80
0
0.18
3.30
3.30
0.30
Dimensions (mm)
NOM
MAX
NOTE
0.90
1.00
0.02
0.05
0.20 REF
1
0.25
0.30
5.00
3.45
5.00
3.45
0.50 BSC
0.213
0.1
0.40
0.1
0.2
3.55
2
3.55
2
0.50
Tolerances of Form and Position
aaa
bbb
ccc
REF:
0.15
0.10
0.10
JEDEC, MO-220, VARIATION VHHD-5.
NOTES:
1. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. FALLS WITHIN JEDEC, MO-220, VARIATION VHHD-5.
3. ALL DIMENSIONS ARE IN MILLIMETRES.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JEDEC 95-1 SPP-002.
5. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
7. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
Figure 9 32 pin 5x5 QFN Package Wolfson Type C
w
August 2006, Rev 2.2
8
WAN_0118
FL: 40 PIN QFN PLASTIC PACKAGE 6 X 6 X 0.9 mm BODY, 0.50 mm LEAD PITCH
D2
31
DM037.B
DETAIL 1
40
D
1
30
EXPOSED
GROUND 6
PADDLE
INDEX AREA
(D/2 X E/2)
4
A
E
E2
21
10
aaa C
2X
11
20
e
b
BOTTOM VIEW
1
bbb M C A B
aaa C
2X
TOP VIEW
ccc C
A3
AA
A
0.08 C
7
DD
CC
BB
A1
SIDE VIEW
C
5
DETAIL 2
SEATING PLANE
L
L1
W
T
A3
b
Exposed lead
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
H
L
T
W
MIN
0.80
0
0.18
4.00
4.00
0.30
DETAIL 1
G
H
Half etch tie bar
DETAIL 2
Dimensions (mm)
NOM
MAX
0.90
1.00
0.02
0.05
0.20 REF
0.25
6.00 BSC
4.15
6.00 BSC
4.15
0.50 BSC
0.213
0.1
0.40
0.1
Dimensions (mm)
Symbols
NOTE
0.30
1
4.25
2
4.25
2
AA
BB
CC
DD
L1
MIN
0.235
0.235
0.181
0.181
0.03
NOM
MAX
NOTE
7
7
7
7
0.15
0.50
0.2
Tolerances of Form and Position
aaa
bbb
ccc
REF:
0.15
0.10
0.10
JEDEC, MO-220, VARIATION VJJD-2.
NOTES:
1. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. FALLS WITHIN JEDEC, MO-220, VARIATION VJJD-2.
3. ALL DIMENSIONS ARE IN MILLIMETRES.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JEDEC 95-1 SPP-002.
5. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
7. DEPENDING ON THE METHOD OF LEAD TERMINATION AT THE EDGE OF THE PACKAGE, PULL BACK (L1) MAY BE PRESENT.
8. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
Figure 10 40 pin 6x6 QFN Package Wolfson Type C
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August 2006, Rev 2.2
9
WAN_0118
DM029.E
FL: 48 PIN QFN PLASTIC PACKAGE 7 X 7 X 0.9 mm BODY, 0.50 mm LEAD PITCH
D2
SEE DETAIL 1
D
D2/2
48
37
L
INDEX AREA
(D/2 X E/2)
1
36
EXPOSED
GROUND 6
PADDLE
E2/2
E2
E
SEE DETAIL 2
25
12
13
24
e
aaa C
2X
b
2X
BOTTOM VIEW
aaa C
TOP VIEW
ccc C
(A3)
A
0.08 C
SIDE VIEW
A1
DETAIL 1
DETAIL 3
DETAIL 2
R = 0.3MM
W
G
H
b
Exposed lead
Terminal
tip
e/2
EXPOSED
GROUND
PADDLE
T
(A3)
Datum
1
C
SEATING PLANE
e
R
Half etch tie bar
DETAIL 3
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
H
L
T
W
aaa
bbb
ccc
REF
Dimensions (mm)
NOM
MAX
0.90
1.00
0.05
0.02
0.20 REF
0.18
0.25
0.30
7.00 BSC
5.00
5.15
5.25
7.00 BSC
5.00
5.15
5.25
0.5 BSC
0.213
0.1
0.50
0.30
0.4
0.1
0.2
Tolerances of Form and Position
0.15
0.10
0.10
MIN
0.80
0
NOTE
1
JEDEC, MO-220, VARIATION VKKD-2
NOTES:
1. DIMENSION b APPLIED TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. ALL DIMENSIONS ARE IN MILLIMETRES
3. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-002.
4. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
5. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
Figure 11 48 pin 7x7 QFN Package Wolfson Type C
w
August 2006, Rev 2.2
10
WAN_0118
DM039.B
FL: 64 PIN QFN PLASTIC PACKAGE 9 X 9 X 0.9 mm BODY, 0.50 mm LEAD PITCH
D2
SEE DETAIL 1
D2/2
49
D
64
L
1
48
EXPOSED
GROUND 6
PADDLE
INDEX AREA
(D/2 X E/2)
E2/2
E2
E
SEE DETAIL 2
16
33
aaa C
2X
32
17
e
2X
b
BOTTOM VIEW
aaa C
TOP VIEW
ccc C
(A3)
A
0.08 C
SEATING PLANE
SIDE VIEW
DETAIL 1
DETAIL 2
DETAIL 3
W
45
degrees
T
(A3)
Terminal
tip
e/2
0.35mm
G
H
b
Exposed lead
Datum
1
C
A1
e
R
Half etch tie bar
DETAIL 3
Symbols
A
A1
A3
b
D
D2
E
E2
e
G
H
L
T
W
aaa
bbb
ccc
REF
Dimensions (mm)
NOM
MAX
0.90
1.00
0.05
0.02
0.20 REF
0.18
0.25
0.30
9.00 BSC
7.00
7.15
7.25
9.00 BSC
7.00
7.15
7.25
0.5 BSC
0.165
0.1
0.50
0.30
0.40
0.1
0.2
Tolerances of Form and Position
0.15
0.10
0.10
MIN
0.80
0
NOTE
1
JEDEC, MO-220, VARIATION VMMD-2
NOTES:
1. DIMENSION b APPLIED TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP.
2. ALL DIMENSIONS ARE IN MILLIMETRES
3. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-002.
4. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
5. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE.
6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING.
Figure 12 64 pin 9x9 QFN Package Wolfson Type C
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WAN_0118
PCB DESIGN CONSIDERATIONS
The PCB design rules when using the QFN packages are fundamentally no different to those for
other more well known packages. The most important considerations are those effects that occur
during the PCB assembly process, which do affect the PCB land layout.
The most obvious difference is the presence of a large thermal die paddle on the bottom side of the
device. Concern is also often shown to the pull-off strength of the QFN device when simply using the
pads to fix the package. For added strength and improved thermal dissipation characteristics, the die
paddle should ideally be soldered to the PCB in addition to the pins.
ROUTING OF TRACES
Traces should be routed straight out from the peripheral pads to a minimum of 500um beyond the
device extremities. Traces should not be routed inwards to a via at the expense of all or part of the
thermal die paddle as there would be a strong possibility of the via shorting to the die paddle. For
QFN Type A packages (see Figures 5 & 6 above) traces from the corner pads should not be routed
perpendicularly as there would be a strong possibility of the trace shorting to the corner tie bars. This
corner area should also be free of other signal traces or copper plane areas that are connected to
different ground planes than that of the die paddle. Figure 21 below, shows a good example layout
where all of the above and below recommendations have been considered and adhered to.
THERMAL DISSIPATION
To allow the heat generated through this large pad to dissipate, the area under the device may
require the inclusion of a thermal landing on the component side of the PCB equal in size to the
maximum size of the device thermal die paddle (it is also recommended to place a thermal landing
on the opposite side of the PCB) connected to analogue ground using a number of thermal vias,
approximately 0.33mm (0.013 inches) diameter. These thermal vias should be completely connected
(flooded over) to the thermal landing(s) (as well as internal ground planes if using a multilayer PCB)
and should not be confused with “thermal relief” or “web-constructed” vias which are designed with
“spokes” to decrease thermal transfer through the PCB. The number of vias will depend upon device
package size, but as a guide the pitch between the vias should be between 0.74mm and 1.27mm. In
Figures 13 – 19 below, 3x3 vias are used for the packages. In Figure 20, the 9X9 package’s size
allows an additional 8 vias. Figures 13 - 20 are not to scale for the purpose of clarity.
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WAN_0118
QFN FOOTPRINTS DIMENSIONS
Figure 13 24 Pin 4x4 QFN Footprint
Figure 14 28 Pin 4x4 COL QFN Footprint
Figure 15 28 Pin 4x4 QFN Footprint
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WAN_0118
Figure 16 28 Pin 5x5 QFN Footprint
Figure 17 32 Pin 5x5 QFN Footprint
Figure 18 40 Pin 6x6 QFN Footprint
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WAN_0118
Figure 19 48 Pin 7x7 QFN Footprint
Figure 20 64 Pin 9x9 QFN Footprint
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WAN_0118
SOLDER MASK AND STENCIL DESIGN CONSIDERATIONS
The greater complexity of the QFN footprint due to the inclusion of the die paddle also means that
the solder mask used during assembly will be of equal complexity. To prevent the solder of the die
paddle transgressing onto the land pads during reflow, the solder mask should overlap the thermal
pad outer edges by at least 100um. This overlap will prevent transgression to the land pads even in
the worst case scenario.
As per Figure 21, the vias should be left bare or untented. This minimizes the presence of voids and
prevents outgassing during reflow. Additionally, if the application permits the use of plated through
hole vias, then the bottom side soldermask should have a clearance around the vias equal in size to
the one on the top side.
Figure 21 32 Pin 5x5 QFN Design Guide
STENCIL DESIGN FOR PERIMETER PADS
The stencil should be 1:1 or 90% of the PCB pad size and should be laser cut for accuracy and
electro-polished which helps in smoothing the stencil sidewalls. The recommended stencil thickness
used is 0.075mm to 0.127mm (0.003in to 0.005in) and the sidewalls of the stencil openings should
be tapered approximately 5 degrees to facilitate better paste release.
DISSECTION OF THE DIE PADDLE SOLDER PASTE STENCIL
If the solder paste coverage of the thermal landing is too big, out-gassing occurs during the reflow
process which may cause defects (splatter, solder balling). As per Figure 21, dividing the thermal
landing into smaller screen openings reduces the risk of solder voiding and allows the solder joints
for the smaller terminal pads to be at the same height as the larger ones. Figure 21 also shows how
the solder paste stencil pattern can minimize the risk of the solder paste wicking down untented vias.
The COL QFN package has no Die Paddle.
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WAN_0118
SOLDER PASTE RECOMMENDATIONS AND REFLOW PROFILE
Due to the size, pitch and depth of the stencil apertures for the QFN package it is recommended that
type 3 no-clean solder pastes be used for printing. For reflow it is recommended an IR or Forced
Convection system be used or a combination system of IR and Forced Convection. For further
information on soldering, please refer to Wan_0158.
INSPECTION OF SOLDER JOINTS AFTER REFLOW
Due to the pad layout of the QFN the solder joints are formed underneath the package and are not
visible. It is recommended that to ensure the joints are soldered sufficiently x-ray inspection be
utilized whenever possible. Visual inspection may be used for a cursory inspection to ensure that
there is no obvious solder bridging.
Shown below in Figure 22 is a typical x-ray inspection of the Wolfson 32pin QFN.
Figure 22 X-Ray Inspection of 5mm×5mm 32 pin QFN
As can be seen the solder has reflowed to form acceptable joints and there is minimal voiding in the
thermal die paddle and pad solder joints, also there is no bridging visible between the joints. X-Ray
inspection can also be useful in highlighting possible process problems such as solder balling and
voiding which are often an indication of poorly optimized reflow profiles.
For a cursory visual inspection it should be noted that Wolfson currently provides its packages with
two different QFN package types as mentioned. However it should be noted that solder fillets up the
side of the QFN package are not required for acceptability of soldering; as specified in international
standard IPC-A-610D; whether fillets are formed or not does not affect the mechanical strength and
reliability of the solder joints. There is no difference in the mechanical strength and reliability between
the two packages; the differences are only cosmetic.
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WAN_0118
APPENDIX:
Extract from IPC-A-610D (Copyright IPC, Bannockburn, IL. Used by permission)
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WAN_0118
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WAN_0118
APPLICATION SUPPORT
If you require further information or require technical support, please contact Wolfson
Microelectronics Applications group through the following channels:
Email:
Telephone:
Fax:
Mail:
apps@wolfsonmicro.com
(+44) 131 272 7070
(+44) 131 272 7001
Applications at the address on the last page.
or contact your local Wolfson representative.
Additional information may be made available from time to time on our web site at:
http://www.wolfsonmicro.com
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WAN_0118
IMPORTANT NOTICE
Wolfson Microelectronics plc (“Wolfson”) products and services are sold subject to Wolfson’s terms and conditions of sale, delivery
and payment supplied at the time of order acknowledgement.
Wolfson warrants performance of its products to the specifications in effect at the date of shipment. Wolfson reserves the right to
make changes to its products and specifications or to discontinue any product or service without notice. Customers should
therefore obtain the latest version of relevant information from Wolfson to verify that the information is current.
Testing and other quality control techniques are utilised to the extent Wolfson deems necessary to support its warranty. Specific
testing of all parameters of each device is not necessarily performed unless required by law or regulation.
In order to minimise risks associated with customer applications, the customer must use adequate design and operating
safeguards to minimise inherent or procedural hazards. Wolfson is not liable for applications assistance or customer product
design. The customer is solely responsible for its selection and use of Wolfson products. Wolfson is not liable for such selection
or use nor for use of any circuitry other than circuitry entirely embodied in a Wolfson product.
Wolfson’s products are not intended for use in life support systems, appliances, nuclear systems or systems where malfunction can
reasonably be expected to result in personal injury, death or severe property or environmental damage. Any use of products by the
customer for such purposes is at the customer’s own risk.
Wolfson does not grant any licence (express or implied) under any patent right, copyright, mask work right or other intellectual
property right of Wolfson covering or relating to any combination, machine, or process in which its products or services might be or
are used. Any provision or publication of any third party’s products or services does not constitute Wolfson’s approval, licence,
warranty or endorsement thereof. Any third party trade marks contained in this document belong to the respective third party
owner.
Reproduction of information from Wolfson datasheets is permissible only if reproduction is without alteration and is accompanied by
all associated copyright, proprietary and other notices (including this notice) and conditions.
Wolfson is not liable for any
unauthorised alteration of such information or for any reliance placed thereon.
Any representations made, warranties given, and/or liabilities accepted by any person which differ from those contained in this
datasheet or in Wolfson’s standard terms and conditions of sale, delivery and payment are made, given and/or accepted at that
person’s own risk. Wolfson is not liable for any such representations, warranties or liabilities or for any reliance placed thereon by
any person.
ADDRESS:
Wolfson Microelectronics plc
26 Westfield Road
Edinburgh
EH11 2QB
United Kingdom
Tel :: +44 (0)131 272 7000
Fax :: +44 (0)131 272 7001
Email :: apps@wolfsonmicro.com
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