ST AN2639 APPLICATION NOTE

AN2639

Application note

Soldering recommendations and package information

for Lead-free ECOPACK® microcontrollers

Introduction

STMicroelectronics microcontrollers support various types of Lead-free ECOPACK
package to meet customer requirements.

The mounting technologies are Surface mount technology (SMT), and Through hole
technology (THT). Beside the available mounting technology, the choice is often driven by
technical and economical concerns. This application note describes the various package
types used for microcontrollers, introduces the different mounting technologies, and gives
soldering recommendations.

®

May 2009 Doc ID 14016 Rev 2 1/15

www.st.com

Contents AN2639

Contents

1 Lead-free packages at STMicroelectronics . . . . . . . . . . . . . . . . . . . . . . . 3

2 Microcontroller packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3 SMD presentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3.1 Handling SMDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

4 Soldering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.1 Soldering methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Bending leads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Insertion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

4.2 Soldering recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.3 Compatibility with leaded soldering process . . . . . . . . . . . . . . . . . . . . . . . 7

4.4 Reflow soldering conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

5 SMD gluability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

6 Dry packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6.1 Pop-corn effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

6.2 Dry pack opening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

7 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

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AN2639 Lead-free packages at STMicroelectronics

1 Lead-free packages at STMicroelectronics

STMicroelectronics is fully committed to environment protection and sustainable
development and started in 1997 a voluntary program for removing polluting and hazardous
substances from all devices. In 2000, a strategic program, named ECOPACK has been
officially launched to develop and implement solutions leading to environment friendly
packaging and ban progressively Pb and other heavy metals from our manufacturing lines.
ECOPACK is a registered trademark of STMicroelectronics.

STMicroelectronics ECOPACK products are RoHS compliant according to EU 2002/95/EC
directive.

For more detailed information please go to http://www.st.com.

Note: RoHS stands for ‘Restriction of the use of certain Hazardous Substances’. The directive

2002/95/EC of the European Parliament and of the Council of 27th January 2003 on the
RoHS in electrical and electronic equipment entered into force on 13th of February 2003.
The aim of this directive is to ban heavy metals (Lead, Mercury, Cadmium, Hexavalent
Chromium) and two brominated compounds (PBB and PBDE). The directive will be
applicable throughout EU by 1st July 2006.

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Microcontroller packages AN2639

2 Microcontroller packages

The different packages available at STMicroelectronics for microcontrollers are described

Table 1.

Table 1. Microcontroller package types

Surface mount technology Through hole technology

Package Pin count Package Pin count

SON 8,16 PDIP .3 8, 16, 20
SOW 16, 20, 24, 28, 34 Shrink PDIP .4 32S
PLCC 44, 520 PDIP .6 28, 42S, 56S
PQFP 44, 52, 80, 100, 144, 208
LQFP 32, 44, 48, 52, 64, 80, 100, 128
LFBGA,TFBGA Up to 144
PBGA Up to 480
TSSOP 20

(1)

VFQFPN 8, 20, 24, 36, 40, 48, 64

1. Larger package portfolio can be proposed upon request.

Through hole technology (THT) and Surface mount technology (SMT) imply different
soldering technologies leading to different constraints.

In THT, the package body is exposed to relatively low temperatures (< 150 °C) because the
lead extremities are only dipped in the soldering alloy, whereas in SMT the whole package
body is exposed to a very high temperature (> 240 °C) during reflow soldering process.

In addition, molding compounds used for integrated circuit encapsulation absorb moisture
from the ambient medium. During rapid heating in solder reflow process (see Section 4:

Soldering for more details), this absorbed moisture can vaporize, generating pressure at

lead frame pad / silicon to plastic interfaces in the package, with a risk of package cracking
and potential degradation of device reliability.

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AN2639 SMD presentation

3 SMD presentation

Unlike through hole technology where leads are inserted into the printed circuit board, SMD
(surface mount device) package is attached directly onto mounting pads of the substrate.
SMT is extensively used in electronic applications because it has the following advantages:

●

Packages are smaller and support higher pin counts

●

Packages are light and compact, thus reducing system sizes

●

Mounting can be done on either side of the PCB

●

No cost for drilling holes into the PCB

Surface mount technology also comes along with a few disadvantages:

●

Increased sensitivity to soldering heat because of their thinner dimension

●

Soldering conditions harder to determine (use of finer structures and higher pin count)

3.1 Handling SMDs

Though the intrinsic reliability of SMD packages is now excellent, the use of inappropriate
techniques or unsuitable tools during mechanical handling can affect the long term reliability
of the device, or even destroy it.

When handling a SMD package, it is strongly recommended to use adapted tools such as
vacuum pipes to avoid touching the pins as much as possible. Manual handling could affect
lead coplanarity and cause lead contamination or scratches that could generate solderability
problems. It is also not allowed to widen the interval between two consecutive pins.

Doc ID 14016 Rev 2 5/15