NIS3001 ON Semiconductor, NIS3001 Datasheet - Page 13

• Manufacturer Part Number: NIS3001
• Description: Integrated Driver And Mosfet Power Chip For Synchronous Buck Controllers
• Manufacturer: ON Semiconductor

an advanced Quad Flat−pack No−Lead Package (QFN) or
commonly referred to as a Leadless Package. Because the
QFN(Leadless) platform represent the latest in surface
mount packaging technology, it is important that the design
of the Printed Circuit Board (PCB), as well as the assembly
process, follow the suggested guidelines outlined in this
document.
NIS3001 Package Overview
either a single or multiple semiconductor devices to be
connected together within a leadless package.
semiconductor devices within one package. This package
style was chosen due to its excellent thermal dissipation
and reduced electrical parasitics.
critical issues must be considered:
SMD and NSMD pad configurations
commonly used for surface mount leadless QFN style
packages. These different I/O configurations are:
solder mask pulled away from the solderable metallization,
while the SMD pads have the solder mask over the edge of
the metallization, as shown in Figure 17. With the SMD
Pads, the solder mask restricts the flow of solder paste on
the top of the metallization which prevents the solder from
flowing along the side of the metal pad. This is different
from the NSMD configuration where the solder will flow
around both the top and the sides of the metallization.
Various ON Semiconductor components are packaged in
The QFN platform offers a versatility, which allows
In this case the NIS3001 Package contains multiple
When surface mounting this package onto a PCB, two
This document will address both of these critical issues.
There are two different types of PCB pad configurations
As their titles describe, the NSMD contact pads have the
Printed Circuit Board Design Considerations
Solder Mask
Overlay
1. Printed Circuit Board Design
2. Board Mounting Process.
1. Non Solder masked Defined (NSMD)
2. Solder Masked Defined (SMD)
Solder Mask
Opening
Figure 17. Comparison of NSMD versus SMD
NSMD
INTRODUCTION
pads.
SMD
APPLICATION INFORMATION
Solderable
Pad
http://onsemi.com
NIS3001
13
configuration since defining the location and size of the
copper pad is easier to control than the solder mask. This
is based on the fact that the copper etching process is
capable of a tighter tolerance than the solder masking
process.
concentration point where the solder wets to the pad on top
of the lead. This stress concentration point is eliminated
when the solder is allowed to flow down the sides of the
leads in the NSMD configuration.
NSMD Pad Configurations
located at least a 0.076mm (0.003in) away from the edge
of the solderable pad. This spacing is used to compensate
for the registration tolerances of the solder mask, as well as
to insure that the solder is not inhibited by the mask as it
reflows along the sides of the metal pad. The dimensions
of the soldermask openings are shown in Figure 18 for a
preferred non−soldermask configuration.
match those of the pads on the package as shown in
Figure 19. The 1:1 ratio between the package’s pad
configuration, and that of the PCB’s, is desired for optimal
placement accuracy and reliability. Please note that
NIS3001 Footprint shows smaller exposed pad openings
compared with the recommended PCB layout. Die attach
pads on the footprint were divided into smaller exposed
pads to help reduce the risk of solder voiding during reflow
mounting to the package
Typically, the NSMD pads are preferred over the SMD
In addition, the SMD pads will inherently create a stress
When dimensionally possible, the solder mask should be
The dimensions of the PCB’s solderable pads should
12X
0.941
Figure 18. NSMD Openings for PCB Layout
4.720
1.765
0.508
12X
3.810
6.745
1.765
6.274
9.992