Additional Information, DS9, Jan.

2006

Recommendations for Printed

Circuit Board Assembly of
Infineon TSLP/TSSLP Packages
Edition 2006-01-10
Published by
Infineon Technologies AG
81726 München, Germany
© Infineon Technologies AG 2006.
All Rights Reserved.

Legal Disclaimer
The information given in this document shall in no event be regarded as a guarantee of conditions or
characteristics (“Beschaffenheitsgarantie”). With respect to any examples or hints given herein, any typical values
stated herein and/or any information regarding the application of the device, Infineon Technologies hereby
disclaims any and all warranties and liabilities of any kind, including without limitation warranties of
non-infringement of intellectual property rights of any third party.

Information
For further information on technology, delivery terms and conditions and prices please contact your nearest
Infineon Technologies Office (www.infineon.com).

Warnings
Due to technical requirements components may contain dangerous substances. For information on the types in
question please contact your nearest Infineon Technologies Office.
Infineon Technologies Components may only be used in life-support devices or systems with the express written
approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure
of that life-support device or system, or to affect the safety or effectiveness of that device or system. Life support
devices or systems are intended to be implanted in the human body, or to support and/or maintain and sustain
and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may
be endangered.
 Assembly & Interconnect Technology

1 Package Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Package Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 ESD Protective Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1 Workplace-ESD Protective Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2 Equipment for Personal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.3 Production Installations and Processing Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Packing of Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3 Storage and Transportation Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Printed Circuit Board (PCB) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 Routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 PCB Pad Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3 Pad Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4 PCB Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1 Solder Stencil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2 Solder Paste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3 Component Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4 Soldering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4.1 Double-Sided Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.4.2 Processing of Moisture-Sensitive Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.4.3 Special Notes for Green Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5 Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.6 Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5 Rework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1 Tooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.2 Device Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3 Site Redressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4 Reassembly and Reflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Additional Information 3 DS9, 2006-01-10

 Assembly & Interconnect Technology

Package Description

1 Package Description
Infineon’s TSLP/TSSLP (Thin (Super) Small Leadless Package, Figure 1) is a green, leadframe based, small,
leadless, land grid array package. It is the preferred package for space and weight limited applications like cellular
phones and digital cameras.

Features
• Smallest xyz-package dimension for diodes/transistors
• Lead-free package
• Halogen-free package
• Environmental friendly packing due to paper tape
• Flexible package platform with short time tooling of new package sizes
• Flip chip or wire bond interconnection
• Possibility of multi-chip packages
• Possibility of cavity packages
• Better electrical performance for RF applications
• Better thermal performance in comparison to standard discrete package

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Figure 1 TSLP/TSSLP Cross Section

Additional Information 4 DS9, 2006-01-10

 Assembly & Interconnect Technology

Package Handling

2 Package Handling

2.1 ESD Protective Measures

Semiconductor devices are normally electrostatic discharge sensitive devices (ESDS) requiring specific
precautionary measures in respect of handling and processing. Only in this way is it possible to insure that the
components can be inserted into assemblies without becoming damaged. Discharging of electrostatic charged
objects over an IC, caused by human touch or by processing tools may cause high current respectively high
voltage pulses, which may damage or even destroy sensitive semiconductor structures. On the other hand ICs
may also be charged during processing. If discharging takes place too quickly (“hard” discharge), it may cause
load pulses and damages, either. ESD protective measures must therefore prevent a contact with charged parts
as well as a charging of the ICs. Protective measures against ESD include both the handling and processing and
the packing of ESDS. A few hints are provided below on handling and processing.

2.1.1 Workplace-ESD Protective Measures

• Standard marking of ESD protected areas
• Access controls, with wrist strap and footwear testers
• Air conditioning
• Dissipative and grounded floor
• Dissipative and grounded working and storage areas
• Dissipative chairs
• Earth bonding point for wrist strap
• Trolleys with dissipative surfaces and wheels
• Suitable shipping and storage containers
• No sources of electrostatic fields

2.1.2 Equipment for Personal

• Dissipative/conductive footwear or heel straps
• Suitable smocks
• Wrist strap with safety resistor
• Volume conductive gloves or finger cots
• Regular training of staff

2.1.3 Production Installations and Processing Tools

• Machine and tool parts made of dissipative or metallic materials
• No materials having thin insulating layers for sliding tracks
• All parts reliably connected to ground potential
• No potential difference between individual machine and tool parts
• No sources of electrostatic fields
Detailed information on ESD protective measures may be obtained from the ESD Specialist through Area Sales
Offices. Our recommendations are based on the internationally applicable standards IEC 61340-5-1 and
ANSI/ESD S2020.

Additional Information 5 DS9, 2006-01-10

 Assembly & Interconnect Technology

Package Handling

2.2 Packing of Components

List of relevant standards which should be considered

IFX packs according to the IEC 60286-* series (The IEC 60286-3 is similar to the EIA 481-*)
IEC 60286-1 Packaging of components for automatic handling - Part 1:
Tape packaging of components with axial leads on continuous tapes
IEC 60286-2 Packaging of components for automatic handling - Part 2:
Tape packaging of components with unidirectional leads on continuous tapes
IEC 60286-3 Packaging of components for automatic handling - Part 3:
Packaging of surface mount components on continuous tapes
IEC 60286-4 Packaging of components for automatic handling - Part 4:
Stick magazines for dual-in-line packages
IEC 60286-5 Packaging of components for automatic handling - Part 5:
Matrix trays
IEC 60286-6 Packaging of components for automatic handling - Part 6:
Bulk case packaging for surface mounting components
Moisture Sensitive Surface Mount Devices are packed according to IPC/JEDEC J-STD-033A July 2002:
Handling, Packing, Shipping and Use of Moisture/Reflow Sensitive Surface Mount Devices
Detailed packing drawings: Packing Information (Internet)

Other references
ANSI/EIA-481-* Standards Proposal No. 5048, Proposed Revision of ANSI/EIA-481-B 8 mm through 200 mm
Embossed Carrier Taping and 8 mm & 12 mm Punched Carrier Taping of Surface Mount
Components for Automatic Handling (if approved, to be published as ANSI/EIA-481-C)
EIA-726 8 mm Punched & Embossed Carrier Taping of Surface Mount Components for Automatic
Handling of Devices Generally Smaller than 2.0 mm x 1.2 mm
EIA-747 Adhesive Backed Punched Plastic Carrier Taping of Singulated Bare Die and Other Surface
Mount Components for Automatic Handling of Devices Generally Less than 1.0 mm Thick
EIA/IS-763 Bare Die and Chip Scale Packages Taped in 8 mm & 12 mm Carrier Tape for Automatic Handling
EIA-783 Guideline Orientation Standard for Multi-Connection Package (Design Rules for Tape and Reel
Orientation)

2.3 Storage and Transportation Conditions

Improper transportation and unsuitable storage of components can lead to a number of problems during
subsequent processing, such as poor solderability, delamination and popcorn effects.

List of relevant standards which should be considered

IEC 60721-3-0 Classification of environmental conditions: Part 3:
Classification of groups of environmental parameters and their severities; introduction
IEC 60721-3-1 Classification of environmental conditions: Part 3:
Classification of groups of environmental parameters and their severities; Section 1: Storage
IEC 60721-3-2 Classification of environmental conditions: Part 3:
Classification of groups of environmental parameters and their severities; Section 2: Transportation
IEC 61760-2 Surface mounting technology - Part 2:
Transportation and storage conditions of surface mounting devices (SMD) - Application guide
IEC 62258-3 Semiconductor Die Products - Part 3:
Recommendations for good practice in handling, packing and storage
ISO 14644-1 Clean rooms and associated controlled environments Part 1:
Classification of airborne particulates

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 Assembly & Interconnect Technology

Package Handling

Table 1 General Storing Conditions - Overview

Product Condition for Storing
Wafer/Die N2 or MBB (IEC 62258-3)
Component - moisture sensitive MBB1) (JEDEC J-STD-033*)
Component - not moisture sensitive 1K2 (IEC 60721-3-1)
1) MBB = Moisture Barrier Bag

Maximum storage time

The conditions to be complied with in order to ensure problem-free processing of active and passive components
are described in standard IEC 61760-2.

Internet links to standards institutes

American National Standards Institute (ANSI)
Electronics Industries Alliance (EIA)
Association Connecting Electronics Industries (IPC)

Additional Information 7 DS9, 2006-01-10

 Assembly & Interconnect Technology

Printed Circuit Board (PCB)

3 Printed Circuit Board (PCB)

3.1 Routing
Generally the printed circuit board design and construction is a key factor for achieving a high reliability of the
solder joints. Some areas and mounting positions on a board are more critical regarding reliability (for example the
region around or at the opposite PCB side of RF frames, connectors and packages). If possible it is attempted to
avoid the mounting of bigger packages in this areas and small devices like TSLP/TSSLP packages are preferably
located there. This may lead to a lower reliability compared to standardized boardlevel reliability tests.

3.2 PCB Pad Design

The solder pads have to be designed to assure optimum manufacturability and reliability. Generally two basic
types of solder pads are commonly used:
• “Solder mask defined” (SMD) pad: The copper pad is larger than the solder mask opening above this pad. Thus
the land area is defined by the opening in the solder mask.

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Figure 2 SMD Pad

• “Non solder mask defined” (NSMD) pad: Around each copper pad there is solder mask clearance. It is necessary
to specify the dimensions and tolerances of the solder mask clearance in this way, that no overlapping of the
solder pad by solder mask occurs (depending on PCB manufacturers tolerances, 75 µm is a widely used value).

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Figure 3 NSMD Pad

Because NSMD pads provide more space for routing and result in a higher solder joint reliability (also the side
walls of the lands are wetted by the solder, which results in less stress concentration), NSMD type is
recommended for the solder pads on the PCB.
For small TSLP/TSSLP packages also another option of NSMD pads can be used. In this case the solder mask
opening is larger than the outline of the package. This helps to prevent the tilting of devices when the solder mask
is thicker than the height of the copper pad + solder joint.
A mixture between SMD and NSMD pads for one component is not recommended. Heavy misalignment between
solder mask and board pads can lead to an unbalanced wettable surfaces and solder joints.

Attention: The copper pad (NSMD) and solder mask openings (SMD) dimensions which have been tested
by Infineon as best solution for each type of package are shown in extra PDF-Files available in
the internet under "additional information" ➞ "TSLP-x-y_pads&apertures.pdf".

Additional Information 8 DS9, 2006-01-10

 Assembly & Interconnect Technology

Printed Circuit Board (PCB)

Generally: To avoid tilted devices bigger pads of the package are divided up in smaller pads on the PCB. If
possible, small pads are slightly expanded to have a better printability.
Because of thermal and RF performance reasons the PCB design may include vias. The vias serve to conduct the heat
and/or RF-signals into deeper layers of the board. Dependent on the package size a different number of vias is possible.
Especially for small packages the vias should not be placed under the device. If this is not possible the vias should be covered
by solder resist or should be plugged to avoid a filling of them with solder, which may cause voiding and a smaller stand-off.
Also microvias can serve to get a better thermal and RF performance. They can be placed inside the solder pads
and therefore are a preferred solution. Be aware that their flatness has to be sufficient, because deep dips inside
the pads may cause solder joint voiding.

3.3 Pad Surfaces

The solder pads must have good wettability to the soldering material (solder paste). All finishes listed here are well
proven for SMT assembly, but especially for fine pitch applications the quality of the plating gets more important.
Therefore Hot Air Solder Levelling finish can be used, but the flatness of the single pads has to be good, not to
bring on soldering problems. The properties of some preservatives are listed in Table 2.

Table 2 Properties of Some Solderability Preservative Layers on PCBs

Finish Typ. Layer Properties Concerns
Thickness
[µm]
HASL (SnAg) >5 cheap, widely usage, know how uneven surface, formation of
(Hot Air Solder Leveling) in fabrication humps, flatness of single pads has
to be good for fine pitch applications
Electroless Tin 0.3 - 1.2 solder joint consists only of long-term stability of protection
copper and solder, no further may be a concern, baking of
metal is added to the solder joint PCB may be critical
Electroless Silver 0.2 - 0.5 solder joint consists only of long-term stability of protection
copper and solder, no further may be a concern, baking of
metal is added to the solder joint PCB may be critical
Electroless Ni / 3 - 7 / 0.05 - 0.15 good solderability protection, expensive, concerns about
Immersion Au high shear force values brittle solder joints
(ENIG)
Galvanic Ni/Au > 3 / 0.1 - 2 only for thicker layers, expensive, not recommended
typically used for connectors for solder pads
OSP typical 1 cheap, simple, fast and must be handled carefully to
(Organic Solderability automated fabrication avoid damaging the OSP; not as
Preservatives) good long-term stability as other
coatings; at double-sided reflow
only suitable with inert gas reflow

The question about the best preservative surface can not be answered generally. It depends strongly on board
design, pad geometry, components on board or process conditions. The best choice for one application needn’t
be the best one for another application. In literature the test results of solderability, wetting force and wetting time
for several preservative layers are not always coincident.

Special notes for green (“G”) packages:

The PCB must be able to resist the higher temperatures which are occurring at the lead-free process.
This question should be discussed with the PCB-supplier. Generally spoken, the wettability of tin-lead solder
paste on the described surface platings is better compared to lead-free solder paste.

Additional Information 9 DS9, 2006-01-10

 Assembly & Interconnect Technology

PCB Assembly

4 PCB Assembly

4.1 Solder Stencil

The solder paste is applied onto the PCB metal pads by screen printing. The volume of the printed solder paste
is determined by the stencil aperture and the stencil thickness. In most cases the thickness of a stencil has to be
matched to the needs of all components on the PCB. For TSLP packages it is recommended to use 80-120 µm
thick stencils. For TSSLP it is recommended to use 100 µm or less.
Size and shape of the apertures are also defined in the PDF-files available in the internet under
"additional information" ➞ "TSLP-x-y_pads&apertures.pdf".
To ensure a uniform and high solder paste transfer to the PCB, laser cut (mostly made from stainless steel) or
electroformed stencils (Nickel) should be preferred. Generally rounded corners of the apertures (radius ~50 µm)
can be supportive for the paste release.

4.2 Solder Paste

Solder paste consists of solder alloy and a flux system. Normally the volume is split into about 50% alloy and 50%
flux. In term of mass this means approx. 90 wt% alloy and 10 wt% flux system. The flux system has the function
to remove the contaminations from the solder joints during the soldering process. The capability of removing
contaminations is given by the respective activation level. The solder paste metal alloy has to be of leaded eutectic
or near-eutectic composition (SnPb or SnPbAg) or lead-free composition (SnAgCu whereas Ag 3-4%, Cu 0.5-1%).
A “no-clean” solder paste is preferred, because cleaning under the soldered TSLP/TSSLP may be difficult. The
paste must be suitable for printing the solder stencil aperture dimensions, Type 3 paste should be sufficient. Solder
paste is sensitive to age, temperature and humidity. Please notice the handling recommendations of the paste
manufacturer.

4.3 Component Placement

TSLP/TSSLP packages have to be placed accurately according to their geometry. The positioning of the packages
by hand is not recommended.
Component placement accuracies of ±70 µm are obtained with modern automatic component placement
machines using vision systems. With these systems both the PCB and the components are optically measured
and the components are placed on the PCB at their programmed positions. The fiducials on the PCB are located
either on the edge of the PCB for the entire PCB or additionally on individual mounting positions (local fiducials).
They are detected by a vision system immediately before the mounting process. Recognition of the packages is
performed by a special vision system, enabling a correct centering of the complete package.
The maximum tolerable misplacement of the components is 35% of the metal pad width on the PCB. In
consequence, for example for the TSLP-3-1 the device pad to PCB pad misalignment has to be better than 70 µm
to assure a robust mounting process.
Also higher misplacement can result in good soldered devices. In this case the self centering effect during reflow
can align the package to the board pads. Only the customer can decide under the consideration of his special
processes and materials if the self centering effect can be used to tolerate a higher misplacement rate.
The following remarks are important:
• Especially on large boards local fiducials close to the device can compensate a large amount of PCB
tolerances.
• Due to the fact that the outer dimensions of the package are very accurate (±50 µm) an alignment according
to the outline is no problem. Of course it is also possible to use the lead recognition capabilities of the
placement system.
• To ensure the identification of the packages by the vision system, an adequate lighting as well as the correct
choice of the measuring modes is necessary. The accurate settings can be taken from the equipment manuals.
• Too much placement force can lead to squeezed out solder paste and causes solder joint shorts or beading.
On the other hand too low placement force can lead to insufficient contact between package and solder paste
and this can lead to open solder joints or badly centered packages.

Additional Information 10 DS9, 2006-01-10

 Assembly & Interconnect Technology

PCB Assembly

4.4 Soldering
Soldering determines the yield and quality of assembly fabrication to a very large extent. Generally all standard
reflow soldering processes
• vapor phase
• forced convection
• infrared (with restrictions)
and typical temperature profiles are suitable for board assembly of the TSLP/TSSLP. Wave soldering is not
possible. At the reflow process each solder joint has to be exposed to temperatures above solder liquidus for a
sufficient time to get the optimum solder joint quality, whereas overheating the PCB with its components has to be
avoided. Please refer to the bar code label on the packing for the peak package body temperature. When using
infrared ovens without convection special care may be necessary to assure a sufficiently homogeneous
temperature profile for all solder joints on the PCB, especially on large, complex boards with different thermal
masses of the components, including those under the TSLP/TSSLP. The most recommended type is forced
convection reflow. Nitrogen atmosphere can generally improve solder joint quality, but is normally not necessary
for soldering tin-lead metal alloys.
The temperature profile of a reflow process is one of the most important factors of the soldering process. The
temporal progression of the temperature profile is divided into several phases, each with a special function.
Figure 4 shows a general forced convection reflow profile for soldering TSLP/TSSLP packages. Table 3 shows an
example of the key data of such a solder profile for Tin-lead and for lead-free alloys. The single parameters are
influenced by various facts, not only by the package. It is essential to follow the solder paste manufactures
application notes, too. Additionally, most PCBs contain more than one package type and therefore the reflow
profile has to be matched to all components’ and materials’ demands. We recommend measuring the solder joints’
temperatures by thermocouples under the respective packages. It has to be considered, that components with
large thermal masses don’t heat up in the same speed as lightweight components, and also the position and the
surrounding of the package on the PCB, as well as the PCB thickness can influence the solder joint temperature
significantly. Therefore no concrete temperature profile can be given.

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Additional Information 11 DS9, 2006-01-10

 Assembly & Interconnect Technology

PCB Assembly

Table 3 Example for the Key Data of a Forced Convection Reflow Solder Profile
Parameter Tin-lead Alloy Lead-free Alloy Main Requirements
(SnPb or SnPbAg) (SnAgCu) From
Preheating rate 2.5 K/s 2.5 K/s Flux system (Solder paste)
Soaking temperature 140 - 170°C 140 - 170°C Flux system (Solder paste)
Soaking time 80 s 80 s Flux system (Solder paste)
Peak temperature 225°C 245°C Alloy (Solder paste)
Reflow time over Liquidus 60 s 60 s Alloy (Solder paste)
Cool down rate 2.5 K/s 2.5 K/s

4.4.1 Double-Sided Assembly

TSLP/TSSLP packages are generally suitable for mounting on double-sided PCBs. That means that in a first step
one side of the PCB is fitted with components and soldered. Afterwards the second side of the PCB is fitted with
components and soldered again.

4.4.2 Processing of Moisture-Sensitive Components

Generally TSLP/TSSLP packages are not moisture-sensitive and are classified as MSL1.
Certain products using the TSLP as package are more sensitive and have therefore their own classification. For
these moisture-sensitive products it is necessary to control the moisture content of the components. The
penetration of moisture into the package mold compound is generally caused through exposure to the ambient air
for a few days. Moisture absorption leads in many cases to moisture concentrations in the component which are
high enough to destroy the package during the soldering process (“popcorn effect”). Hence the necessity to dry
moisture-sensitive components, to seal them in a moisture-resistant bag and only to remove them immediately
prior to processing (soldering onto the PCB) is given. The permissible time (from opening the moisture barrier bag
until the final soldering process) that a component can remain unprotected in an environment with a level of
humidity approximating to real-world conditions (e.g. 30°C/60% RH) is a measure of the sensitivity of the
component to ambient humidity (Moisture Sensitivity Level, MSL). The most commonly applied standard
IPC/JEDEC J-STD-033* thus defines eight different MSLs (see Table 4). Please refer to the “Moisture Sensitivity
Caution Label” on the packing material, which contains information about the moisture sensitivity level of your products.

Table 4 Moisture Sensitivity Levels (acc. to IPC/JEDEC J-STD-033*)

Level Floor Life (out of bag)
Time Conditions
1 Unlimited ≤ 30°C / 85% RH
2 1 year ≤ 30°C / 60% RH
2a 4 weeks ≤ 30°C / 60% RH
3 168 hours ≤ 30°C / 60% RH
4 72 hours ≤ 30°C / 60% RH
5 48 hours ≤ 30°C / 60% RH
5a 24 hours ≤ 30°C / 60% RH
6 Mandatory bake before use. After bake, must be reflowed within ≤ 30°C / 60% RH
the time limit specified on the label.

Internet Link to Association Connecting Electronics Industries (IPC)

Additional Information 12 DS9, 2006-01-10

 Assembly & Interconnect Technology

PCB Assembly

If moisture-sensitive components have been exposed to ambient air longer than the specified time according to
their MSL, or the humidity indicator card dot 10% is wet (read 1 minute after bag opening), the packages have to
be baked prior to the assembly process. Please refer to IPC/JEDEC J-STD-033* for bake procedure. Baking a
package too often can cause solderability problems due to oxidation and/or intermetallic growth. Notice that
packing material possibly can not withstand the baking temperature. See imprints/labels on the respective packing
for maximum temperature.

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Figure 5 Humidity Indicator

4.4.3 Special Notes for Green Packages

TSLP/TSSLP packages are in principle green. In combination with other green packages the following has to
be considered.
Like in Tin-lead-process, generally all commonly used reflow soldering processes (vapor phase, forced
convection, infrared) are suitable for board assembly. But due to a higher peak temperature at the lead-free
process, some equipment can reach the limits of their technical capability. Normally reflow with forced
convection is chosen. Due to the aggravated conditions at the lead-free process, nitrogen atmosphere may
reduce oxidation and improve the solder joint quality. Be aware, that the increasing temperature stress may
worsen the MSL. Therefore the data for lead-free packages names 2 MSLs: One for a lower reflow peak
temperature (tin-lead) and one for a higher reflow peak temperature (lead-free). Each one is valid for the
respective application.

4.5 Cleaning
After the reflow soldering process some flux residues can be found around the solder joints. If a “no-clean” solder
paste has been used for solder paste printing, the flux residues usually don’t have to be removed after the
soldering process. Be aware, that cleaning under a TSLP/TSSLP package is difficult because of the small gap
between package substrate and PCB and is therefore not recommended. Whether the solder joints have to be
cleaned, however, the cleaning method (e.g. ultrasonic, spray or vapor cleaning) and solution has to be selected
with consideration of the packages to be cleaned, the used flux in the solder paste (rosin-based, water-soluble,
etc.), environmental and safety aspects. Removing/Drying even of small residues of the cleaning solution should
also be done very thorough. Contact the solder paste manufacturer for recommended cleaning solutions.

Additional Information 13 DS9, 2006-01-10

 Assembly & Interconnect Technology

PCB Assembly

4.6 Inspection
A visual inspection of the solder joints with conventional AOI (automatic optical inspection) systems is limited to
the outer surface of the solder joints. In most cases these are visible and can be judged by looking at them from
the side (not from the top like most of the AOI systems). Therefore the significance of an optical inspection is poor.
Only big misplacement and wrong polarity can be checked.

Figure 6 Typical Side View of TSLP Solder Joints

The only reasonable method to realize an efficient inline control is the implementation of AXI (automatic X-ray
inspection) systems. AXI systems are available as 2D and 3D solutions. They usually consist of an X-ray camera
and the hard- and software needed for inspection, controlling, analyzing and data transfer routines. These systems
enable the user to detect soldering defects like poor soldering, bridging, voiding and missing parts quite reliable.
But other defects like broken solder joints are not easily detectable by X-ray. For the acceptability of electronic
assemblies please refer also to the IPC-A-610C standard.

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Visible are solder joints, wires (dark structures), board pads (under solder resist) and trip lines (light
structures). The round structures are vias (from the top to the first inner layer or from the first inner
layer to the second inner layer).

Additional Information 14 DS9, 2006-01-10

 Assembly & Interconnect Technology

PCB Assembly

Cross sectioning of a soldered package as well as dye penetrant analysis can serve as tools for sample monitoring
only, due to their destructive character. But they help to get an idea about the quality of the solder joint,
intermetallic compounds and voids.

Figure 8 Cross Section of a TSLP Solder Joint (lead-free)

Special notes for green (“G”) packages:

Lead-free solder joints look different than tin-lead (SnPb) solder joints. Tin-lead joints have a bright and shiny
surface, a dull surface is an indicator for an insufficient solder joint. Lead-free solder joints don’t have this bright
surface. Lead-free solder joints are dull and grainy. These surface properties are caused by the irregular
solidification of the solder, as the used solder alloys are not exactly eutectic (like the 63Sn37Pb solder alloy).
This means that SnAgCu-solders don’t have a melting point but a melting range of some degrees. Although
lead-free solder joints have this dull surface, this does not mean that lead-free joints are of lower quality or
weaker than the SnPb joints. This characteristic makes it necessary to instruct the inspection personnel how
these new lead-free joints look like, and/or to adjust optical inspection systems to lead-free solder joints.

Additional Information 15 DS9, 2006-01-10

 Assembly & Interconnect Technology

Rework

5 Rework
If a defect component is observed after board assembly the device can be removed and replaced by a new one.
Repair of components' single solder joints is difficult. In any case the device has to be removed and at least the
old or a new device has to be soldered onto the board.

5.1 Tooling
The rework process is commonly done on special rework equipment. There are a lot of systems available on the
market, and for processing these packages the equipment should fulfill the following requirements:
• Heating: Hot air heat transfer to the package and PCB is strongly recommended. Temperature and air flow for
heating the device should be controlled. With free-programmable temperature profiles (e.g. by PC controller)
it is possible to adapt the profiles to different package sizes and masses. PCB preheating from underside is
recommended. Infrared heating can be applied, especially for preheating the PCB from underside, but it should
be only supporting the hot air flow from the upside. Instead of air also nitrogen can be used.
• Vision system: The bottom side of the package as well as the site on the PCB should be observable. For
precise alignment of package to PCB a split optic should be implemented. Microscope magnification and
resolution should be appropriate for the pitch of the device.
• Moving and additional tools: The device should be relocatable on the whole PCB area. Placement accuracy is
recommended to be better than ±100 µm. The system should have the capability of removing solder residues
from PCB pads (special vacuum tools).

5.2 Device Removal

If it is intended to send a defect component back to the supplier, please note that during the removal of this
component no further defects must be introduced to the device, because this may hinder the failure analysis at
the supplier. This includes the following recommendations:
• Moisture: According to his moisture sensitivity level, possibly the package has to be dried before removal. If
the maximum storage time out of the dry pack (see label on packing material) is exceeded after board
assembly, the PCB has to be dried according to the recommendations (see Chapter 4.4), otherwise too much
moisture may have been accumulated and damage may occur (popcorn effect).
• Temperatur profile: During soldering process it should be assured that the package peak temperature is not
higher and temperature ramps are not steeper than for the standard assembly reflow process
(see Chapter 4.4).
• Mechanics: Be aware not to apply high mechanical forces for removal. Otherwise failure analysis of the
package can be impossible or PCB can be damaged. For large packages pipettes can be used (implemented
on most rework systems), for small packages tweezers may be more practical.

5.3 Site Redressing

Standard process: After removing the defect component the pads on the PCB have to be cleaned from solder
residues. Before placing a new component it is recommended to apply solder paste on each PCB pad by printing
(special micro stencil) or dispensing. It is recommended to use only no-clean solder paste.
Special process: For low pin count (<10), small TSLP/TSSLP packages also the following procedure can be used.
After removing the defect component the remainding solder on the pads can checked regarding coplanarity and
contaminations. If the solder residues are uniform and clean some flux can be applied by dispension or with a
brush. It is recommended to use only no-clean solder flux. Generally the resulting solder joint (see Chapter 5.4) is
lower, but fulfils the quality requirements.

5.4 Reassembly and Reflow

After preparing the site, the package can be placed onto the PCB. The package is positioned exactly above the
PCB pads, in height just that there is no contact between the package and the PCB and the package is then
dropped into the printed or dispensed flux or solder paste depot (Zero-force-placement). During soldering process
it should be assured that the package peak temperature is adjusted to the used solder and is not higher and
temperature ramps are not steeper than for the standard assembly reflow process (see chapter Chapter 4.4).

Additional Information 16 DS9, 2006-01-10

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