Renesas QFN Mounting Manual
User’s Manual
QFN Mounting Manual
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www.renesas.com
Rev.1.50 Mar2015
Notice
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(2012.4)
QFN Mounting Manual
Table of Contents
1. The QFN Package ............................................................................................................................ 1
1.1 Punching Cut Type (anvil singulation) ..................................................................................................................... 1
1.2 Dicing Cut Type (SAW singulation) ......................................................................................................................... 2
1.3 Lead Surface Processing Specifications .................................................................................................................... 2
2. Mounting Pads ................................................................................................................................. 3
2.1 Pad Structure ............................................................................................................................................................. 3
2.2 Mounting Pad Design Parameters ............................................................................................................................. 4
2.3 Notes on Mounting Pad Design (punching cut type) ................................................................................................ 5
2.4 Mounting Pad Design Examples ............................................................................................................................... 5
3. Solder Paste Printing ........................................................................................................................ 6
3.1 Solder Paste ............................................................................................................................................................... 6
3.2 Stencils ...................................................................................................................................................................... 7
4. Package Placement ......................................................................................................................... 10
4.1 Board Mounting Placement Conditions .................................................................................................................. 10
5. Reflow Thermal Resistance ........................................................................................................... 12
5.1 Storage Prior to Opening Moisture-Proof Packing ................................................................................................. 12
5.2 Storage After Opening Moisture-Proof Packing ..................................................................................................... 12
5.3 Baking ..................................................................................................................................................................... 12
5.4 Number of Reflow Operations ................................................................................................................................ 13
5.5 Reflow Thermal Resistance .................................................................................................................................... 13
5.6 Soldering Temperature ............................................................................................................................................ 14
6. Cleaning ......................................................................................................................................... 15
7. Visual Inspection ........................................................................................................................... 16
7.1 Overview of the QFN Package Pin End Surface ..................................................................................................... 16
7.2 Visual Comparison of Air Reflow and Nitrogen Reflow Mounting ....................................................................... 17
8. On Board Mechanical Stress Test Results ..................................................................................... 18
9. On Board Reliability Test Results ................................................................................................. 19
9.1 Board Mounted Thermal Cycle Test Results (punching cut type, 6 × 6 mm, 0.4 mm pitch) ................................. 19
9.2 Board Mounted Thermal Cycle Test Results (dicing cut type, 5 × 5 mm, 0.5 mm pitch)...................................... 19
9.3 Board Mounted Thermal Cycle Test Results (dicing cut type, 7 × 7 mm, 0.5 mm pitch)...................................... 20
9.4 Board Mounted Thermal Cycle Test Results (dicing cut type: package shape dependency) ................................. 20
10. QFN Reworking (removal from the mounting board) ................................................................. 21
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QFN Mounting Manual 1. The QFN Package
n
1. The QFN Package
The QFN (Quad Flat No-lead) package is a low-profile package with a leadless structure. It is appropriate for use in
portable and other equipment that requires miniaturization and reduced weight. QFN packages are classified by their
formation method into the punching cut and dicing cut types. The remainder of this section presents an overview of these
packages.
1.1 Punching Cut Type (anvil singulation)
This type of QFN package is characterized by an individually molded body with punch press excision. Since the external
leads of the package, in which each cavity is sealed with mold resin, are punched with a die, the leads can be made to
protrude for extremely short distances from the package periphery.
Figure 1.1 Package Top Side Figure 1.2 Package Underside
Mold
resin
Chip
Wire bonding
Lead
Figure 1.3 Basic Structure Figure 1.4 Cross-Section View
Wire bonding
Chip
Lead
Mold resi
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QFN Mounting Manual 1. The QFN Package
1.2 Dicing Cut Type (SAW singulation)
This type of QFN package is characterized by the package being formed by cutting with a rotating blade. Since multiple
packages sealed at the same time are cut apart with a dicing blade (rotating blade), the ends of the leads and the edge of
the package (cut surface) are coplanar.
Figure 1.5 Package Top Side Figure 1.6 Package Underside
Mold resin
Chip
Wire bonding
Chip
Wire bonding
Lead
Lead
Figure 1.7 Basic Structure Figure 1.8 Cross-Section View
1.3 Lead Surface Processing Specifications
See the Renesas web site for the lead surface processing specifications for each QFN package code.
http://www.renesas.com/products/package/information/ic_name_list/index.jsp
Mold resin
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QFN Mounting Manual 2. Mounting Pads
2. Mounting Pads
2.1 Pad Structure
(1) NSMD Type
In this structure, the solder resist does not come over the edges of the mounting pads.
(2) SMD Type
In this structure, the solder resist comes over the edges of the mounting pads.
It is important to consider the characteristics of the lead morphology when designing printed wiring boards. Also, it is
important to be aware that even if the package code is identical, there may be subtle differences in pin dimensions
between individual parts.
Mounting pad
Solder resist
SMD structure
(Solder Masked Defined)
Printed wiring board
(Non Solder Masked Defined)
Figure 2.1 Pad Structures
Mounting pad
NSMD structure
Solder resist
Printed wiring board
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QFN Mounting Manual 2. Mounting Pads
2.2 Mounting Pad Design Parameters
The parameters that determine the mounting pad dimensions include the following.
Soldering strength (1)
Solder mask pattern precision and soldering visual inspectability (2)
Solder bridge tolerance ()
The way the margins for each dimensional area are determined depends on the user’s approach to pattern design and the
application the equipment will be used in. We recommend that users design QFN printed wiring board mounting pads
based on the approach shown below, which is similar to that for QFP packages.
L2b2
b
Lp
Lp = Pin flat section length
b = Pin width
γ
E2
e
b2
β
β
1
2
L2 ≥ Lp + β
b ≤ b2 ≤ e − γ (b2: mounting pad width)
1
+ β2 (L2: mounting pad length)
Figure 2.2 Mounting Pad Design Parameters
Table 2.1 Design Reference Values Unit: mm
e 0.80 0.50 0.40
1 0 to 0.30 0 to 0.30 0 to 0.20
2 0 to 0.30 0 to 0.30 0 to 0.20
0.10 to 0.30 0.10 to 0.30 0.10 to 0.20
Notes: 1. The mounting pad pitch must be the linear pin spacing (pin pitch) for the package being mounted.
2. We do not recommend mounting, on the wiring board, the lead that is exposed at the package corner (die pad
hanging lead) for the punching cut type QFN package.
3. If required, we recommend that users analyze the package end land 1 dimension taking contact with corner
exposed leads into account.
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QFN Mounting Manual 2. Mounting Pads
2.3 Notes on Mounting Pad Design (punching cut type)
In the punching cut type QFN package, part, or all, of the lead (hanging lead) that supports the die pad in the corner, is
exposed at the package end. (We do not recommend soldering to this section.)
Since the characteristics of the semiconductor device itself may be affected if electrical contact is made to the corner pin,
we recommend that users consider mounting pad design that takes contact with the corner pin section into account.
A design example for the P-VQFN48-6x6-0.4 package is presented below.
Contact with the die pad hanging lead is avoided by designing 1 to be shorter than that for other pads.
No Exposed Pad Exposed Pad
Die pad hanging lead Die pad hanging lead
Exposed Pad
0.65
>γ
Die pad
Figure 2.3 Die Pad Hanging Lead Example Figure 2.4 Design Example
when a Die Pad is Present
2.4 Mounting Pad Design Examples
See the Renesas web site for mounting pad design examples for each QFN package code.
http://www.renesas.com/products/package/information/ic_name_list/index.jsp
0.85
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QFN Mounting Manual 3. Solder Paste Printing
3. Solder Paste Printing
3.1 Solder Paste
The main components of solder paste are solder powder and flux. The particular solder paste used should be chosen
based on the usage conditions adopted.
(1) Solder Powder
Due to the desire to eliminate lead from manufacturing processes due to environment considerations, a variety of leadfree metal compositions (mainly Sn-Ag-Cu family compositions) are widely used. The different lead-free alloys are used
according to the type of application and the soldering method used. Furthermore, there is a range of particle sizes in these
powders, and the particle size affects the printability and other characteristics of the paste. Good results can be obtained,
especially for fine-pitch (0.5 mm and under) mounting, if a fine powder with particle diameter of 40 µm or smaller and
also with a narrow distribution of particle sizes is used. Note, however, that for finer powders, there are concerns that
solder balls due to surface oxidation and adverse influence on the wettability may occur. Therefore, extra care is required
when handling solder paste that uses solder powders such as those discussed above.
Type 3: 0.045 mm to 0.020 mm Type 4: 0.038 mm to 0.020 mm Type 5: 0.025 mm to 0.010 mm
Figure 3.1 Visual Appearance of Solder Powders
(2) Flux
Flux improves solderability in the soldering process in three ways: (1) it excludes oxides from components and the
pattern surface, (2) it prevents re-oxidation during soldering, and (3) it reduces the surface tension of the melted solder.
Flux includes four components that assist in soldering: tackifiers, thixotropic agents, solvents, and activators. These are
used for the following purposes.
Tackifier resins: Component mountability, metal cleaning, reoxidation prevention
Thixotropic agents: Preventing separation of solder powder and flux, and droop prevention
Activating agents: Metal cleaning
Solvents: Forming the paste
There are three main types of flux: rosin fluxes, alloy resin fluxes, and water soluble fluxes. In addition, rosin fluxes are
classified into three types by their degree of activation: R (rosin flux), RMA (weakly activated flux), and RA (activated
flux). Table 3.1 lists their features.
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