NXP Semiconductors AN10365, Примечание к применению

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AN10365_3 © NXP B.V. 2008. All rights reserved.
Application note Rev. 03 — 22 April 2008 7 of 24
NXP Semiconductors
AN10365
Surface mount reflow soldering description
Note that a solder resist defined layout requires the application of a solder resist bridge
between two terminals. There is a minimum width of solder resist that can be applied by
board suppliers. This fact, in combination with a maximum solder resist placement
accuracy, implies that solder resist defined layouts are not always possible. For IC
packages with a small pitch, it is no longer possible to apply a solder resist bridge
between two terminals, and a Cu defined or combination layout must be used.
If a solder land is solder resist defined, the Cu must extend far enough underneath the
solder resist to allow for tolerances in Cu etching and solder resist placement during board
production. Similarly, if a solder land is Cu defined, the solder resist must lie sufficiently far
away from the solder land to prevent bleeding of the solder resist onto the Cu pad. Typical
values for these distances are 50
µ
m to 75
µ
m.
The footprints referred to in this document indicate the areas that can be soldered.
The footprint shown in Figure 2 is redefined for both a solder resist and a Cu layout, in
Figure 5 . Note that the overlap/gap between the solder resist and the Cu is 0.05 mm in
this particular example.
2.2 IC packages
IC packages may be divided into groups in various ways. In this document, they are
categorized according to the shape of the terminals, as this has the largest influence on
board assembly. Accordingly, the three main IC family types are the leaded packages
(such as QFPs), the leadless packages with solder balls (such as BGAs) or leadless
packages with solder lands (such as HVQFNs). Apart from the terminals, packages may
have heat sinks and/or ground connections.
Fig 5. Solder land dimensions for SOT266-1 package, either solder resist or Cu defined
001aac833
0.65 mm
0.05 mm
1.35 mm
0.05 mm
1.35 mm
0.4 mm
1.35 mm
0.4 mm
0.05 mm 0.05 mm
footprint
dimensions
solder resist defined copper defined
0.65 mm 0.4 mm 0.65 mm