AMIS-30624 I2C Microstepping Motordriver
Data Sheet
20.0 Soldering
20.1 Introduction to Soldering Surface Mount Packages
This text gives a very brief insight to a complex technology. A more in-depth account of soldering ICs can be found in the AMIS “Data
Handbook IC26; Integrated Circuit Packages” (document order number 9398 652 90011). There is no soldering method that is ideal for
all surface mount IC packages. Wave soldering is not always suitable for surface mount ICs, or for printed-circuit boards with high
population densities. In these situations re-flow soldering is often used.
20.2 Re-flow Soldering
Re-flow soldering requires solder paste (a suspension of fine solder particles, flux and binding agent) to be applied to the PCB by
screen printing, stencilling or pressure-syringe dispensing before package placement. Several methods exist for reflowing; for example,
infrared/convection heating in a conveyor type oven.
Throughput times (preheating, soldering and cooling) vary between 100 and 200 seconds depending on the heating method. Typical re-
flow peak temperatures range from 215 to 260°C. The top-surface temperature of the packages should preferably be kept below 230°C.
20.3 Wave Soldering
Conventional single wave soldering is not recommended for surface mount devices (SMDs) or PCBs with a high component density, as
solder bridging and non-wetting can present major problems. To overcome these problems, the double-wave soldering method was
specifically developed.
If wave soldering is used the following conditions must be observed for optimal results:
• Use a double-wave soldering method comprising a turbulent wave with high upward pressure followed by a smooth laminar wave.
• For packages with leads on two sides and a pitch (e):
o
Larger than or equal to 1.27mm, the footprint longitudinal axis is preferred to be parallel to the transport direction of the
PCB;
o
Smaller than 1.27mm, the footprint longitudinal axis must be parallel to the transport direction of the PCB. The footprint
must incorporate solder thieves at the downstream end.
• For packages with leads on four sides, the footprint must be placed at a 45º angle to the transport direction of the PCB. The
footprint must incorporate solder thieves downstream and at the side corners.
During placement and before soldering, the package must be fixed with a droplet of adhesive. The adhesive can be applied by screen
printing, pin transfer or syringe dispensing. The package can be soldered after the adhesive is cured. Typical dwell time is four seconds
at 250°C. A mildly-activated flux will eliminate the need for removal of corrosive residues in most applications.
20.4 Manual Soldering
Fix the component by first soldering two diagonally-opposite end leads. Use a low voltage (24V or less) soldering iron applied to the flat
part of the lead. Contact time must be limited to 10 seconds at up to 300°C.
When using a dedicated tool, all other leads can be soldered in one operation within two to five seconds between 270 and 320°C.
Table 35: Soldering Process
Soldering Method
Package
Wave
Not suitable
Re-flow(1)
Suitable
Suitable
Suitable
Suitable
Suitable
BGA, SQFP
HLQFP, HSQFP, HSOP, HTSSOP, SMS
PLCC (3) , SO, SOJ
Not suitable(2)
Suitable
LQFP, QFP, TQFP
Not recommended(3)(4)
Not recommended(5)
SSOP, TSSOP, VSO
Notes:
(1) All surface mount (SMD) packages are moisture sensitive. Depending upon the moisture content, the maximum temperature (with respect to time) and body size
of the package, there is a risk that internal or external package cracks may occur due to vaporization of the moisture in them (the so called popcorn effect). For
details, refer to the drypack information in the “Data Handbook IC26; Integrated Circuit Packages; Section: Packing Methods.”
(2) These packages are not suitable for wave soldering as a solder joint between the printed-circuit board and heatsink (at bottom version) can not be achieved, and
as solder may stick to the heatsink (on top version).
(3) If wave soldering is considered, then the package must be placed at a 45° angle to the solder wave direction. The package footprint must incorporate solder
thieves downstream and at the side corners.
(4) Wave soldering is only suitable for LQFP, TQFP and QFP packages with a pitch (e) equal to or larger than 0.8mm; it is definitely not suitable for packages with a
pitch (e) equal to or smaller than 0.65mm.
(5) Wave soldering is only suitable for SSOP and TSSOP packages with a pitch (e) equal to or larger than 0.65mm; it is definitely not suitable for packages with a
pitch (e) equal to or smaller than 0.5mm.
AMI Semiconductor – Apr. 2007, Rev 3.1, M-20664-003
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