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Application NoteSoldering Considerations for Power Modules

Kyle Norell, Andrew Kutzler
ABSTRACTTI has a large portfolio of power modules offered in different types of packages. This application note offers anoverview of several module package types and provides some guidance on soldering topics and considerations.

Table of Contents
1 Introduction.............................................................................................................................................................................22 Package Types........................................................................................................................................................................ 2
2.1 MicroSiP.............................................................................................................................................................................2
2.2 QFN Overmolded............................................................................................................................................................... 2
2.3 QFN Open Frame...............................................................................................................................................................3
2.4 Leaded............................................................................................................................................................................... 3
2.5 QFN-FCMOD..................................................................................................................................................................... 33 Package CAD/CAE Symbols and Footprints........................................................................................................................44 Soldering................................................................................................................................................................................. 54.1 MSL Ratings.......................................................................................................................................................................5
4.2 Reflow Profile..................................................................................................................................................................... 5
4.3 Back Side PCB Mounting Considerations..........................................................................................................................65 Rework During Prototyping................................................................................................................................................... 86 References.............................................................................................................................................................................. 87 Revision History......................................................................................................................................................................9

List of Figures
Figure 2-1. LMZM23601 (36V, 1A) Module in MicroSiP Package............................................................................................... 2Figure 2-2. LMZ36002 (60V, 2A) Module in Leadframe-based Overmolded QFN Package....................................................... 2Figure 2-3. TPSM84A21 (14V, 10A) Module in PCB Laminate Based Overmolded QFN Package............................................ 2Figure 2-4. TPSM846C23 (15V, 35A) Module in PCB Laminate Open Frame QFN Package.................................................... 3Figure 2-5. LMZ14203 (42V, 3A) Module in Leaded Overmolded PMOD Package.................................................................... 3Figure 2-6. TPSM365R6 (65V, 0.6A) QFN- FCMOD (Flipchip on Lead Module) Package......................................................... 3Figure 3-1. Downloadable CAD Files.......................................................................................................................................... 4Figure 4-1. MSL Information Available at Various Locations....................................................................................................... 5Figure 4-2. Component Held by the Solder Surface Tension Around the Pad Perimeter............................................................6Figure 4-3. Component Held by the Solder Surface Tension Across the Pad Area.................................................................... 6

List of Tables
Table 4-1. Back Side Feasibility With Second Reflow................................................................................................................. 7Trademarks
MicroSiP™ is a trademark of Texas Instruments.
All trademarks are the property of their respective owners.

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Soldering Considerations for Power Modules

1Introduction

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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

2 Package Types
2.1 MicroSiPThe 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 2-1 shows an illustration of thispackage construction.

INDUCTORCAPACITORSUBSTRATEEMBEDDED IC

Figure 2-1. LMZM23601 (36V, 1A) 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 theinductor, 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 2-2 and Figure 2-3 for examples ofthese QFN module packages.

INDUCTORPROGRAMMINGCOMPONENTS

COPPERLEADFRAME

POWER ICINTEGRATED POWER ICINTEGRATED INDUCTORCAPACITORS AND OTHERPASSIVES
MULTILAYER PCB LAMINATE

MOLDING COMPOUNDMOLDING COMPOUND

ALL SIGNALS ACCESSIBLE
FROM PERIMETERLARGE POWER PADS FOR ELECTRICAL
AND THERMAL PERFORMANCEFigure 2-2. LMZ36002 (60V, 2A) Module in
Leadframe-based Overmolded QFN Package

2Soldering Considerations for Power Modules

LARGE POWER PADS FOR ELECTRICAL
AND THERMAL PERFORMANCE

Figure 2-3. TPSM84A21 (14V, 10A) Module in PCB
Laminate Based Overmolded QFN Package

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Package Types

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 ofthe inductor for potential heat transfer. See Figure 2-4 for an illustration.

INTEGRATED INDUCTORINTEGRATED POWER ICCAPACITORS AND OTHERPASSIVES
MULTILAYER PCB LAMINATENO MOLDING COMPOUND
DIRECT ACCESS TO INDUCTOR TOP

Figure 2-4. TPSM846C23 (15V, 35A) 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 easylayout. Figure 2-5 provides an illustration of this package construction.
INTEGRATED INDUCTORCAPACITORS AND RESISTORSDUAL COPPER LEADFRAME
POWER ICMOLDING COMPOUNDLARGE GND PADLEADSBOTTOM VIEW

Figure 2-5. LMZ14203 (42V, 3A) Module in Leaded Overmolded PMOD Package

2.5 QFN-FCMOD
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 easylayout. provides an illustration of this package construction.

LEADS
POWER ICBOOTSRAP CAPACITOR
INDUCTOR

Figure 2-6. TPSM365R6 (65V, 0.6A) QFN- FCMOD (Flipchip on Lead Module) Package
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3Package CAD/CAE Symbols and Footprints

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3 Package CAD/CAE Symbols and Footprints
To streamline the design process, many of TI's modules have CAD symbols available for download underthe 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 3-1. Downloadable CAD Files

4Soldering Considerations for Power Modules

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Soldering

4 Soldering
4.1 MSL Ratings
Electronic components can absorb moisture. When going through the reflow process, the absorbed moistureis 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 MoistureSensitivity Level (MSL) rating which defines the floor life between the time the drypack packing is opened andthe 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 isprovided 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 4-1.

PACKAGE OPTION ADDENDUM SECTION OF THE DATASHEET:QUALITY SECTION OF THE PRODUCT FOLDER ON TI.COM:

PACKAGING LABEL:

Figure 4-1. 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 themaximum 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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4.3 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 asecond reflow while the component is upside-down. The feasibility of the component staying attached to theboard 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 PCBSURFACE TENSIONFORCE OF SOLDER
ON THE PAD PERIMETER

PAD

PAD
COMPONENTGRAVITATIONAL FORCE

Figure 4-2. 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 thecomponent pads. The empirical model dictates 22mg/mm of maximum recommended ratio of component mass
to total pad perimeter.
4.3.2 Method 2 - Solder Surface Area

SURFACE TENSIONFORCE OF SOLDER
ON THE PAD AREAAPPLICATION PCBPADPADCOMPONENTGRAVITATIONAL FORCE

Figure 4-3. 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 47mg/mm2 of maximum recommended
ratio of component mass to total pad area.

6Soldering Considerations for Power Modules

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Soldering4.3.3 Back Side PCB Mounting Evaluation of TI Modules
Table 4-1 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
Table 4-1. Back Side Feasibility With Second Reflow
FEASIBILITYWITHOUT 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

YMicroSiP

48

10.7

2.0

LMZ30602YQFN Overmolded

850

31.4

8.5

LMZ30604YQFN Overmolded

850

31.4

8.5

LMZ30606YQFN Overmolded

850

31.4

8.5

LMZ31503YQFN Overmolded

1260

38.8

10.2

LMZ31506YQFN Overmolded

1260

38.8

10.2

LMZ31520

NQFN Overmolded

4960

67.2

25.5

LMZ31530NQFN Overmolded

4960

67.2

25.5

LMZ31704NQFN Overmolded

1430

68.2

13.8

LMZ31707NQFN Overmolded

1430

68.2

13.8

LMZ31710

NQFN Overmolded

1430

68.2

13.8

LMZ34002

Y

QFN Overmolded

891

26.3

9.8LMZ34202

N

QFN Overmolded

1475

52.7

13.7

LMZ35003

Y

QFN Overmolded

891

26.3

9.8

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

LMZM33602YQFN Overmolded

468

25.6

4.7

LMZM33603YQFN Overmolded

468

25.6

4.7

LMZM33604NQFN Overmolded

1990

57.7

11.9

LMZM33606NQFN Overmolded

1990

57.7

11.9

TPS82084

Y

MicroSiP

53.5

14.5

2.6

TPS82085

Y

MicroSiP

53.5

14.5

2.6

TPS82130

Y

MicroSiP62.5

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

TPSM41615YQFN Open Frame

1319

28.5

6.4

TPSM41625

YQFN Open Frame

1319

28.5

6.4

TPSM53602YQFN Overmolded

429

37.3

10.5

TPSM53603YQFN Overmolded

429

37.3

10.5

TPSM53604YQFN Overmolded

429

37.3

10.5

TPSM560R6YQFN Overmolded

429

37.3

10.5

TPSM5601R5YQFN Overmolded

429

37.3

10.5

TPSM5D1806Y

QFN Overmolded

235

14.61.7

TLVM13630

Y

QFN Overmolded

123

13.1

1.9

DEVICE

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Table 4-1. Back Side Feasibility With Second Reflow (continued)
DEVICETPSM63603

FEASIBILITYWITHOUT FIXTURE

PACKAGE
TYPE

MASS
(mg)

MASS / A(mg/mm²)

MASS / P(mg/mm)Y

QFN Overmolded

123

13.1

1.9

209

Y

QFN Overmolded

110

13.2

2.9

TPSM84424

NQFN Open Frame

678(1)

170(1)

42.4(1)TPSM84624

NQFN Open Frame

678(1)

170(1)

42.4(1)125(1)

75.5(1)TPSM846C23NQFN Open Frame

2900(1)TPSM846C24NQFN Open Frame

2900(1)125(1)

75.5(1)170(1)

42.4(1)TPSM84824

N

QFN Open Frame

678 (1)TPSM84A21YQFN Overmolded

725

13.6

7.1

TPSM84A22YQFN Overmolded

725

13.6

7.1

TPSM63602YQFN Overmolded

123

9.8

1.5

TPSM63603YQFN Overmolded

123

9.8

1.5

TPSM63604NQFN Overmolded

429

64.5

9.6

TPSM63606NQFN Overmolded

429

64.59.6

TPSM63608NQFN Overmolded

429

64.5

9.6

TLVM13640

N

QFN Overmolded

429

64.5

9.6

TLVM13660

N

QFN Overmolded

748

64.5

9.6

TPSM365R6Y

QFN- FCMOD

103193

TPSM365R3Y

QFN- FCMOD

103

193

TPSM365R15Y

QFN- FCMOD

103

193

TPSM365R1Y

QFN- FCMOD

103

193

TPSM33615

Y

QFN- FCMOD

103

193

TPSM33625

Y

QFN- FCMOD

103

193(1)

Calculation is based on the mass of the exposed inductor, which is the heavy component likely to fall off first.

4.3.4 Reflow FixtureAs suggested by Table 4-1, placing some devices on the back side of the PCB with a second reflow may not befeasible. 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.

5 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 inmind 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 alreadyprior to the rework. Another important point is to follow the MSL requirements for the component. Baking of theboard assembly can be required prior to rework to remove potential moisture and mitigate risk of damage tothe 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 productdata sheet. Open frame and MicroSiP packages have exposed SMT components on top of the module. Thesecomponents 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

Research In Motion, Weight Limits For Double Sided Reflow Of QFNS publication.
Materials Transactions, Determination of Components Candidacy for Second Side Reflow with Lead-Free
Solder publication.

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Revision History

7 Revision History
Changes from Revision B (May 2021) to Revision C (February 2024)
Page• Added QFN-FCMOD Section............................................................................................................................. 3• Added various QFN Overmolded and QFN-FCMOD devices to the Back Side Feasibility with Second Reflowtable.................................................................................................................................................................... 7

Changes from Revision A (September 2020) to Revision B (May 2021)
Page• Added TPSM5601R5 and TPSM63603 devices to the Back Side Feasibility with Second Reflow table...........7Changes from Revision * (December 2019) to Revision A (September 2020)
Page• Updated the numbering format for tables, figures, and cross-references throughout the document. ............... 2• Added TPSM41625 and TPSM5D1806 devices to the Back Side Feasibility with Second Reflow table...........7

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