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Texas Instruments Soldering Considerations for Power Modules Application notes
Application Report
SNVA853 – December 2019
Soldering Considerations for Power Modules
Denislav Petkov and Kyle Norell
ABSTRACT
TI has a large portfolio of power modules offered in different types of packages. This application report
offers an overview of several module package types and provides some guidance on soldering topics and
considerations.
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Contents
Introduction ...................................................................................................................
Package Types ...............................................................................................................
Package CAD/CAE Symbols and Footprints .............................................................................
Soldering ......................................................................................................................
Rework During Prototyping .................................................................................................
References ...................................................................................................................
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List of Figures
1
LMZM23601 (36 V, 1 A) Module in MicroSiP Package ................................................................. 2
2
LMZ36002 (60 V, 2 A) Module in Leadframe-based Overmolded QFN Package................................... 2
3
TPSM84A21 (14V, 10A) module in PCB laminate based overmolded QFN package .............................. 3
4
TPSM846C23 (15 V, 35 A) Module in PCB Laminate Open Frame QFN Package ................................ 3
5
LMZ14203 (42 V, 3 A) Module in Leaded Overmolded PMOD Package ............................................ 4
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Downloadable CAD Files ................................................................................................... 4
7
MSL information Available at Various Locations
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Component Held by the Solder Surface Tension Around the Pad Perimeter .......................................
Component Held by the Solder Surface Tension Across the Pad Area ..............................................
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List of Tables
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Back Side Feasibility with Second Reflow ................................................................................ 7
Trademarks
All trademarks are the property of their respective owners.
1
Introduction
Power modules aim to simplify power supply design by integrating the power converter IC along with an
inductor or inductors, a capacitor or capacitors, and other passive components into a single power module
package. The modules come in different types of packages depending on their voltage ratings, current
ratings, and target applications. This document addresses some common questions about power modules
including the following:
• Package construction details
• MSL ratings and soldering reflow profile
• Back side mounting capability
• Rework guidance for prototyping
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1
Package Types
www.ti.com
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Package Types
2.1
MicroSiP
The MicroSiP package features a substrate with an IC embedded inside and passive components
mounted on top. Usually, the components on top consist of an inductor and capacitors. Figure 1 shows an
illustration of this package construction.
INDUCTOR
CAPACITOR
SUBSTRATE
EMBEDDED IC
Figure 1. LMZM23601 (36 V, 1 A) Module in MicroSiP Package
2.2
QFN Overmolded
The QFN overmolded package can be based on a leadframe or a PCB laminate. The package integrates
the inductor, power IC, along with programming components. The leadframe-based package uses a thick
copper leadframe for routing. The PCB laminate based package uses a thin multilayer PCB for mounting
and routing all of the integrated components and signals. See the illustrations in Figure 2 and Figure 3 for
examples of these QFN module packages.
INDUCTOR
COPPER
LEADFRAME
PROGRAMMING
COMPONENTS
POWER IC
MOLDING COMPOUND
ALL SIGNALS ACCESSIBLE
FROM PERIMETER
LARGE POWER PADS FOR ELECTRICAL
AND THERMAL PERFORMANCE
Figure 2. LMZ36002 (60 V, 2 A) Module in Leadframe-based Overmolded QFN Package
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Package Types
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INTEGRATED POWER IC
INTEGRATED INDUCTOR
CAPACITORS AND OTHER
PASSIVES
MULTILAYER PCB LAMINATE
MOLDING COMPOUND
LARGE POWER PADS FOR ELECTRICAL
AND THERMAL PERFORMANCE
Figure 3. TPSM84A21 (14V, 10A) module in PCB laminate based overmolded QFN package
2.3
QFN Open frame
This QFN package consists of a multilayer laminate PCB with power IC, capacitors, resistors and inductor
mounted on top. There is no molding compound encapsulating the circuitry. There is a direct access to the
top of the inductor for potential heat transfer. See Figure 4 for an illustration.
INTEGRATED INDUCTOR
INTEGRATED POWER IC
CAPACITORS AND OTHER
PASSIVES
MULTILAYER PCB LAMINATE
NO MOLDING COMPOUND
DIRECT ACCESS TO INDUCTOR TOP
Figure 4. TPSM846C23 (15 V, 35 A) Module in PCB Laminate Open Frame QFN Package
2.4
Leaded
The leaded module packages include a dual copper leadframe with a power IC in between the
leadframes. The integrated inductor, capacitor, and any other passives are situated on the top leadframe.
There is molding compound encapsulating the package. There are leads and a large GND pad for good
heat transfer and easy layout. Figure 5 provides an illustration of this package construction.
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Package CAD/CAE Symbols and Footprints
www.ti.com
INTEGRATED INDUCTOR
CAPACITORS AND RESISTORS
DUAL COPPER LEADFRAME
POWER IC
MOLDING COMPOUND
LARGE GND PAD
LEADS
BOTTOM VIEW
Figure 5. LMZ14203 (42 V, 3 A) Module in Leaded Overmolded PMOD Package
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Package CAD/CAE Symbols and Footprints
To streamline the design process, many of TI's modules have CAD symbols available for download under
the Quality and Packaging section of the device product folder on TI.com. The PCB footprints and
schematic symbols are available for download in a vendor neutral .bxl format, which can then be exported
to the leading EDA CAD/CAE design tools formats using the Ultra Librarian Reader.
Figure 6. Downloadable CAD Files
4
Soldering Considerations for Power Modules
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Soldering
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4
Soldering
4.1
MSL ratings
Electronic components can absorb moisture. When going through the reflow process, the absorbed
moisture is rapidly heated. This can result in excessive pressure inside the component package.
Excessive pressure can cause delamination and internal mechanical damage. The electronics industry
has come up with Moisture Sensitivity Level (MSL) rating which defines the floor life between the time the
drypack packing is opened and the time when the component goes through a reflow cycle. The absorption
of moisture on the factory floor prior to PCB mounting is proportional to the ambient temperature and
relative humidity. The MSL specification is provided with respect to 30°C and 60% relative humidity.
The MSL rating for each product can be found in the product data sheet in the package option addendum
section. Alternatively, the MSL rating can be found under the Quality section in module product folder on
TI.com. The MSL rating is also located on the product packaging label. See Figure 7 .
PACKAGE OPTION ADDENDUM SECTION OF THE DATASHEET:
QUALITY SECTION OF THE PRODUCT FOLDER ON TI.COM:
PACKAGING LABEL:
Figure 7. MSL information Available at Various Locations
4.2
Reflow Profile
The maximum reflow temperature and number of allowed reflows can vary from device to device. The
maximum temperature depends on the package volume and thickness. Refer to each data sheet of the
device for the maximum reflow temperature and number of reflows. Refer to the MSL Ratings and Reflow
Profiles Application Note for an example reflow profile based on J-STD-020 and additional soldering
information.
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Soldering
4.3
www.ti.com
Back Side PCB Mounting Considerations
Will the part fall off or stay on the board after a second reflow upside-down?
Some high density applications can require mounting the power module on the back side of the PCB.
Normally, the PCB side with heavy components would be reflowed last. However, in some cases, there
can be heavy components on both sides of the board. In such applications, the power module package
can go through a second reflow while the component is upside-down. The feasibility of the component
staying attached to the board during the second reflow depends on the component mass, component pad
sizes, and the solder alloy surface tension. There are at least two empirical models in the industry to
evaluate the back side mounting feasibility.
4.3.1
Method 1 - Solder Surface Perimeter
APPLICATION PCB
SURFACE TENSION
FORCE OF SOLDER
ON THE PAD PERIMETER
PAD
PAD
COMPONENT
GRAVITATIONAL FORCE
Figure 8. Component Held by the Solder Surface Tension Around the Pad Perimeter
This method of evaluating the back side mounting feasibility was developed by Smith, Connell, and
Christian. The empirical model defines the force of the solder surface tension as a function of the overall
perimeter of the component pads. The empirical model dictates 22 mg/mm of maximum recommended
ratio of component mass to total pad perimeter.
4.3.2
Method 2 - Solder Surface Area
SURFACE TENSION
FORCE OF SOLDER
ON THE PAD AREA
APPLICATION PCB
PAD
PAD
COMPONENT
GRAVITATIONAL FORCE
Figure 9. Component Held by the Solder Surface Tension Across the Pad Area
This method of evaluating the back side mounting feasibility was developed by Liu, Geiger, and
Shangguan. The model considers the overall area of the component pads and dictates 47 mg/mm2 of
maximum recommended ratio of component mass to total pad area.
4.3.3
Back Side PCB Mounting Evaluation of TI Modules
Table 1 contains the back side PCB mounting feasibility evaluation of several TI module families,
considering the following:
• Maximum mass / pad area ≤ 47 mg/mm2
• Maximum mass / pad perimeter ≤ 22 mg/mm
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Soldering Considerations for Power Modules
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Soldering
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Table 1. Back Side Feasibility with Second Reflow
FEASIBILITY
WITHOUT FIXTURE
PACKAGE
TYPE
MASS
(mg)
MASS / A
(mg/mm²)
MASS / P
(mg/mm)
LMZ10500
Y
MicroSiP
37.4
12.4
1.8
LMZ10501
Y
MicroSiP
37.4
12.4
1.8
LMZ21700
Y
MicroSiP
48
10.7
2.0
LMZ21701
Y
MicroSiP
48
10.7
2.0
LMZ30604
Y
QFN Overmolded
506
17.2
4.6
LMZ31506
Y
QFN Overmolded
719
12.1
3.7
LMZ31520
N
QFN Overmolded
8808
103.7
39.4
LMZ31530
N
QFN Overmolded
8808
103.7
39.4
LMZ31704
N
QFN Overmolded
1944
83.8
17.3
LMZ31707
N
QFN Overmolded
1944
83.8
17.3
LMZ31710
N
QFN Overmolded
1944
83.8
17.3
LMZ34202
N
QFN Overmolded
1475
52.7
13.7
LMZ35003
Y
QFN Overmolded
891
25
7.2
LMZ36002
N
QFN Overmolded
1475
52.7
13.7
LMZM23600
Y
MicroSiP
48.5
12.2
1.9
LMZM23601
Y
MicroSiP
48.5
12.2
1.9
LMZM33602
Y
QFN Overmolded
468
25.6
4.7
LMZM33603
Y
QFN Overmolded
468
25.6
4.7
LMZM33604
N
QFN Overmolded
3037
88
18.2
LMZM33606
N
QFN Overmolded
3037
88
18.2
TPS82084
Y
MicroSiP
53.5
14.5
2.6
TPS82085
Y
MicroSiP
53.5
14.5
2.6
TPS82130
Y
MicroSiP
62.5
16.9
3.1
TPS82140
Y
MicroSiP
62.5
16.9
3.1
TPS82150
Y
MicroSiP
62.5
16.9
3.1
TPSM265R1
Y
MicroSiP
37.7
13.9
1.6
TPSM53602
Y
QFN Overmolded
450
12.9
12.3
TPSM53603
Y
QFN Overmolded
450
12.9
12.3
TPSM53604
Y
QFN Overmolded
450
12.9
12.3
TPSM84209
Y
QFN Overmolded
110
13.2
2.9
TPSM84424
N
QFN Open Frame
678 (1)
170 (1)
42.4 (1)
TPSM84624
N
QFN Open Frame
678 (1)
170 (1)
42.4 (1)
75.5 (1)
DEVICE
TPSM846C23
QFN Open Frame
2900
125
(1)
(1)
125
(1)
75.5 (1)
(1)
170 (1)
42.4 (1)
13.6
7.1
TPSM846C24
N
QFN Open Frame
2900
TPSM84824
N
QFN Open Frame
678
TPSM84A22
Y
QFN Overmolded
(1)
4.3.4
N
(1)
725
Calculation is based on the mass of the exposed inductor, which is the heavy component likely to fall off first.
Reflow Fixture
As suggested by Table 1, placing some devices on the back side of the PCB with a second reflow may
not be feasible. In such cases, a reflow fixture can be designed to hold the heavy components during the
second reflow. Contact TI for possible fixture suggestions based on the particular application board
design.
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Rework During Prototyping
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Rework During Prototyping
Solder rework can sometimes be needed during product prototyping. When reworking components on a
PCB, be sure to observe the maximum reflow temperature for the particular module. Also, it is important to
keep in mind the board reflow history and the maximum number of reflow cycles for the particular module.
For example, if the component is mounted on the back of the board, it may have gone through two reflow
cycles already prior to the rework. Another important point is to follow the MSL requirements for the
component. Baking of the board assembly can be required prior to rework to remove potential moisture
and mitigate risk of damage to the module or other components on the board. Proper solder paste stencil
must be used to ensure adequate solder paste coverage. Refer to the suggested solder paste pattern and
solder stencil information in the product data sheet. Open frame and MicroSiP packages have exposed
SMT components on top of the module. These components can also reflow during the rework procedure.
Take care to avoid shifting or moving the exposed these SMT components during the rework, as this can
affect the module operation.
6
References
•
•
8
Smith, Sasha & Connell, David & Christian, Bev. (2010). Weight Limits for Double Sided Reflow of
QFNs.
Liu, Yueli & Geiger, David & Shangguan, Dongkai. (2005). Determination of Components Candidacy
for Second Side Reflow with Lead-Free Solder. Proceedings - Electronic Components and Technology
Conference. 970-976. 10.1109/ECTC.2005.1441389.
Soldering Considerations for Power Modules
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