1995 Oct 26 1728
Philips Semiconductors
Package information Soldering
INTRODUCTION
There is no soldering method that is ideal for all IC
packages. Wave soldering is often preferred when
through-hole and surface mounted components are mixed
on one printed-circuit board. However, wave soldering is
not always suitable for surface mounted ICs, or for
printed-circuits with high population densities. In these
situations reflow soldering is often used.
Thistextgivesaverybriefinsighttoacomplextechnology.
A more in-depth account of soldering ICs can be found in
our “IC Package Databook” (order code 9397 750 0011).
THROUGH-HOLE MOUNTED PACKAGES
Table 1 Types of through-hole mounted packages
Soldering by dipping or wave
The maximum permissible temperature of the solder is
260 C; solder at this temperature must not be in contact
with the joint for more than 5 seconds. The total contact
time of successive solder waves must not exceed
5 seconds.
The device may be mounted to the seating plane, but the
temperature of the plastic body must not exceed the
specified maximum storage temperature (Tstg max). If the
printed-circuit board has been pre-heated, forced cooling
may be necessary immediately after soldering to keep the
temperature within the permissible limit.
Repairing soldered joints
Apply a low voltage soldering iron (less than 24 V) to the
lead(s) of the package, below the seating plane or not
more than 2 mm above it. If the temperature of the
soldering iron bit is less than 300 C it may remain in
contact for up to 10 seconds. If the bit temperature is
between 300 and 400 C, contact may be up to 5 seconds.
SURFACE MOUNTED PACKAGES
Table 2 Types of surface mounted packages
Reflow soldering
Reflow soldering techniques are suitable for all SMD
packages, ease of soldering varies with the type of
package as indicated in Table <.Normal_XRef>3.
The choice of heating method may be influenced by larger
plastic packages (QFP or PLCC with 44 leads, or more). If
infrared or vapour phase heating is used and the large
packages are not absolutely dry (less than 0.1% moisture
content by weight), vaporization of the small amount of
moisture in them can cause cracking of the plastic body.
For more information on moisture prevention, refer to the
Drypack chapter in our “Quality Reference Handbook”
(order code 9397 750 00192).
Reflow soldering requires solder paste (a suspension of
fine solder particles, flux and binding agent) to be applied
totheprinted-circuit board byscreenprinting, stencilling or
pressure-syringe dispensing before package placement.
Several techniques exist for reflowing; for example,
thermal conduction by heated belt. Dwell times vary
between 50 and 300 seconds depending on heating
method. Typical reflow temperatures range from
215 to 250 C.
Preheating is necessary to dry the paste and evaporate
the binding agent. Preheating duration: 45 minutes at
45 C.
TYPE DESCRIPTION
DIP plastic dual in-line package
SDIP plastic shrink dual in-line package
HDIP plastic heat-dissipating dual in-line package
DBS plastic dual in-line bent from a single in-line
package
SIL plastic single in-line package
TYPE DESCRIPTION
SO plastic small outline package
SSOP plastic shrink small outline package
TSSOP plastic thin shrink small outline package
VSO plastic very small outline package
QFP plastic quad flat package
LQFP plastic low profile quad flat package
SQFP plastic shrink quad flat package
TQFP plastic thin quad flat package
PLCC plastic leaded chip carrier
1995 Oct 26 1729
Philips Semiconductors
Package information Soldering
Table 3 Suitability of surface mounted packages for various soldering methods: rating from ‘a’ to ‘d’: ‘a’ indicates most
suitable (soldering is not difficult); ‘d’ indicates least suitable (soldering is achievable with difficulty).
PACKAGE
TYPE
REFLOW METHOD DOUBLE
WAVE
METHOD
INFRARED HOT BELT HOT GAS VAPOUR
PHASE RESISTANCE
SO aaaada
SSOP a a a c d c
TSSOP b b b c d d
VSO bbabab
QFP b b a c a c
LQFP b b a c d d
SQFP b b a c d d
TQFP b b a c d d
PLCC c bbddb
Wave soldering
Wave soldering is not recommended for SSOP, TSSOP,
QFP, LQFP, SQFP or TQFP packages, this is because of
the likelihood of solder bridging due to closely-spaced
leads and the possibility of incomplete solder penetration
in multi-lead devices.
If wave soldering cannot be avoided, the following
conditions must be observed:
•A double-wave (a turbulent wave with high upward
pressure followed by a smooth laminar wave) soldering
technique should be used.
•For SSOP, TSSOP and VSO packages, the longitudinal
axis of the package footprint must be parallel to the
solder flow and must incorporate solder thieves at the
downstream end.
•For QFP, LQFP and TQFP packages, the footprint must
be at an angle of 45 to the board direction and must
incorporate solder thieves downstream and at the side
corners.
Even with these conditions, consider wave soldering only
for the following package types:
•SO
•VSO
•PLCC
•SSOP only with body width 4.4 mm, e.g. SSOP16
(SOT369-1) or SSOP20 (SOT266-1).
•QFP except QFP52 (SOT379-1), QFP100 (SOT317-1,
SOT317-2, SOT382-1) and QFP160 (SOT322-1); these
are not suitable for wave soldering.
•LQFP except LQFP32 (SOT401-1), LQFP48
(SOT313-1,SOT313-2), LQFP64(SOT314-2), LQFP80
(SOT315-1); these are not suitable for wave soldering.
•TQFP except TQFP64 (SOT357-1), TQFP80
(SOT375-1) and TQFP100 (SOT386-1); these are not
suitable for wave soldering.
SQFP are not suitable for wave soldering.
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.
Maximum permissible solder temperature is 260 C, and
maximum duration of package immersion in solder is
10 seconds, if cooled to less than 150 C within 6 seconds.
Typical dwell time is 4 seconds at 250 C.
A mildly-activated flux will eliminate the need for removal
of corrosive residues in most applications.
Repairing soldered joints
Fix the component by first soldering two diagonally-
opposite end leads. Use only a low voltage soldering iron
(less than 24 V) 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 2 to 5 seconds between
270 and 320 C.
