IPC J-STD-030A

Selection and Application

of Board Level Underfill
Materials

Developed by the Underfill Materials Design, Selection and Process Task

Group (5-24f) of the Assembly and Joining Committee (5-20) of IPC

Supersedes: Users of this publication are encouraged to participate in the

J-STD-030 - September 2005 development of future revisions.

Contact:
IPC
3000 Lakeside Drive, Suite 309S
Bannockburn, IL 60015-1249
Phone ( 847) 615-7100
Fax (847) 615-7105
February 2014 IPC J-STD-030A

Table of Contents
1 SCOPE ...................................................................... 1 7.2 Storage Conditions ........................................... 10
1.1 Introduction ......................................................... 1 7.3 Preconditioning ................................................. 11
1.2 Purpose ................................................................ 1 7.4 Pot Life ............................................................. 11
1.3 Definition of Requirements ................................ 1 7.4.1 Viscosity Change .............................................. 11
7.4.2 Flow Rate Change ............................................ 11
2 APPLICABLE DOCUMENTS .................................... 2
7.4.3 Settling Test ...................................................... 11
2.1 IPC ...................................................................... 2
2.2 American Society for Testing and Materials 8 APPLICATION PROCESS ...................................... 11
(ASTM) ............................................................... 2 8.1 Pre-Application Board Preparation .................. 12
2.3 Telcordia Technologies, Inc. .............................. 2 8.2 Application of Capillary Flow Underfill ......... 12
3 TERMS AND DEFINITIONS ...................................... 2 8.2.1 Dispensing Procedures ..................................... 13
8.2.1.1 Dispensing Patterns .......................................... 13
4 BACKGROUND ......................................................... 3
8.2.1.2 Process Parameters ........................................... 14
4.1 Why Is Underfill Needed? ................................. 3
8.2.2 Application Problems ....................................... 14
4.2 Types of Underfill ............................................... 4
8.2.2.1 Air Entrapment ................................................. 14
4.2.1 Capillary Underfill .............................................. 4
8.2.2.2 Gravitational Phase Separation ........................ 14
4.2.2 Fluxing (No-Flow) Encapsulant ......................... 4
8.2.2.3 Dynamic Phase Separation ............................... 15
4.2.3 Removable/Reworkable Underfill ...................... 5
8.2.2.4 Filtering Phase Separation ................................ 15
4.2.4 Cornerbond Adhesive (Dispensed or
Placed Prior to Reflow Process) ........................ 5 8.3 Application of No-Flow/Fluxing Underfill ...... 15
4.2.5 Corner Glue/Corner Tack Underfills 8.3.1 Dispensing Pattern ............................................ 15
(Applied After SMT Reflow) ............................. 5 8.3.2 Dispense Volume .............................................. 15
5 MECHANICAL CONSIDERATIONS ......................... 6 8.3.3 Package Placement ........................................... 15
5.1 Footprint Design ................................................. 6 8.3.4 Application Problems ....................................... 16
5.2 Gap Size .............................................................. 7 8.4 Flow Rate .......................................................... 16
5.3 Pad Redistribution .............................................. 7 8.4.1 Dispense Flow Rate Measurement .................. 16
8.4.2 Underfill Flow Rate .......................................... 16
6 UNCURED UNDERFILL CHARACTERISTICS ........ 7
8.4.3 Flow Out and Bleed ......................................... 16
6.1 Filler Properties .................................................. 7
8.5 Spread/Slump .................................................... 17
6.1.1 Filler Size ............................................................ 7
8.6 Evaluation Methodology .................................. 17
6.1.2 Filler Material Type ............................................ 8
8.6.1 Acoustic Micro-Imaging .................................. 17
6.1.3 Filler Content ...................................................... 8
8.6.2 Destructive Tests for Voiding ........................... 17
6.1.4 Density ................................................................ 8
8.6.3 Assembly to Glass for Flow Visualization ...... 18
6.2 Prepolymer Properties ........................................ 8
8.7 Pot Life (In Dispenser) .................................... 18
6.2.1 Viscosity .............................................................. 8
6.2.2 Gel Time ............................................................. 8 9 CURE PROCESS .................................................... 18
6.3 Material Compatibility ....................................... 8 9.1 Applied Life (After Dispensing) ...................... 18
6.3.1 Flux Compatibility .............................................. 8 9.2 Cure Process for Capillary Flow Underfill ...... 19
6.3.2 Board Surface Compatibility .............................. 9 9.2.1 Process Parameters ........................................... 19
6.3.3 Component Surface Compatibility ..................... 9 9.2.2 Cure Schedule ................................................... 19
6.4 Alpha Particle Emissions ................................... 9 9.2.3 Heating Rate ..................................................... 19
9.2.4 Temperature Sensitivity .................................... 19
7 MATERIALS PACKAGING, HANDLING, AND
STORAGE ............................................................... 10 9.3 Cure Process for No-Flow Underfill ................ 19
7.1 Packaging and Containers ................................ 10 9.4 Void Formation/Outgassing .............................. 20
7.1.1 Voids/Bubbles in Packed Material ................... 10 9.5 Cure Verification ............................................... 20

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IPC J-STD-030A February 2014

10 CURED UNDERFILL CHARACTERISTICS ......... 20 13.6 General Overview of Voiding Conditions

10.1 Appearance ....................................................... 20 and Reliability Impact/Factors ......................... 29
10.1.1 Fillet Formation ................................................ 20 13.7 Workmanship Guidelines for Corner or
Edge Bond Underfills ....................................... 29
10.1.2 Color (Dye/Pigment) ........................................ 20
10.2 Adhesion ........................................................... 21 14 TROUBLESHOOTING .......................................... 30
10.3 Shrinkage and Induced Stress .......................... 21 14.1 Inadequate Flow ............................................... 30
10.4 Young’s Modulus .............................................. 21 14.1.1 Viscosity ............................................................ 30
10.5 Coefficient of Thermal Expansion (CTE) ........ 21 14.1.2 Wetting .............................................................. 30
10.6 Glass Transition Temperature (Tg) ................... 21 14.1.3 Mechanical Blockage ....................................... 30
10.7 Chemical Stability ............................................ 21 14.2 Phase Separation ............................................... 30
10.7.1 Determining Resistance to Solvents ................ 21 14.3 Voids ................................................................. 30
10.8 Moisture Absorption ......................................... 22 14.3.1 Voids Before Cure ............................................ 30
10.9 Hydrolytic Stability .......................................... 22 14.3.2 Voids After Cure ............................................... 30
10.10 Non-Nutrient ..................................................... 22 14.4 Inadequate Cure ................................................ 30
10.11 Surface Insulation Resistance .......................... 22 14.5 Poor Adhesion .................................................. 31
10.12 Electrochemical Migration Resistance ............. 23 14.6 Thermal Cycle Failure ...................................... 31
10.13 Volume Resistivity ............................................ 23
Figures
10.14 Permittivity (Dielectric Constant) .................... 23
Figure 1-1 Comparison of Various Sized Array
11 WORKMANSHIP ................................................... 24 Packages ........................................................... 1

11.1 Substrate Preparation ........................................ 24 Figure 4-1 Both the Flip-Chip and CSP Underfill in
a Flip-Chip CSP Soldered to a PCA ................. 3
11.2 Cleaning Before Underfill ................................ 24
Figure 4-2 Different Material Coverage Types for
11.3 Cleaning After Cure ......................................... 24 Top and X-Sec View (Underfill, Corner
Glue, Epoxy Flux) .............................................. 3
12 PROCESS RELIABILITY ASSESSMENT ............ 24 Figure 4-3 Example of Epoxy Chemical Reaction .............. 4
12.1 Ionic Content .................................................... 24 Figure 4-4 Image of Needle Dispensing of an
12.2 Chemical Resistance ......................................... 24 Underfill (Bottom Side View) ............................. 4
12.3 Mechanical Integrity ......................................... 24 Figure 4-5 Fluxing Underfill Process .................................. 5

12.5 Post Soldering Processes (Capillary Figure 4-6 Reflow Cured Corner Bond Process ................. 6
Underfill) ........................................................... 24 Figure 4-7 Thermally and UV Cured Corner Tacks ............ 6
12.6 Temperature Cycling ........................................ 25 Figure 6-1 SEM Image Showing Poor Underfill
Adhesion to a Bump Due to Flux
13 OTHER CONSIDERATIONS ................................. 26 Residue ............................................................. 9
13.1 Reworkability .................................................... 26 Figure 8-1 Fluxing Underfill ............................................... 12

13.1.1 Rework of Adjacent Components .................... 26 Figure 8-2 Underfill Dispensing ........................................ 13
Figure 8-3 Examples of Dispensing Patterns
13.2 Determination of Cure ...................................... 26
(The Fillet is Shown in a Different
13.3 Thermal Management ....................................... 26 Color for Clarity Only) ...................................... 13
13.4 Workmanship Standards for BGA and Figure 8-4 Image Showing Both Needle Dispensing
CSP Board Level Underfills ............................. 27 and Jetting for Underfilling at the Chip
Level ................................................................ 14
13.4.1 Visual Criteria ................................................... 27
Figure 8-5 Air Entrapment (Underfill was Dispensed
13.4.2 Underfill Voiding Under Devices ..................... 28 on the Left Edge of the Package) ................... 14
13.5 Destructive Inspection ...................................... 29 Figure 8-6 Gravitational Phase Separation ...................... 14

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February 2014 IPC J-STD-030A

Figure 8-7 Dynamic Phase Separation ............................. 15

Figure 8-8 Filtering Phase Separation .............................. 15
Figure 8-9 Underfill Bleed ................................................. 17
Figure 9-1 Filler Settling within Underfill ........................... 18
Figure 10-1 Underfill Adhesion Test .................................... 21
Figure 12-1 Material Property and Thermal Cycling
Response ........................................................ 25
Figure 13-1 Acceptable – Class 1,2,3 ................................ 27
Figure 13-2 Void Comparison ............................................. 28
Figure 13-3 Target – Flat Cross Section that Shows
No Voids in the Underfill Layer ....................... 29
Figure 13-4 Image of a Component with Edgebond
Underfill ........................................................... 29
Figure 13-5 Fillet Width ....................................................... 29
Figure 14-1 Filtering Phase Separation .............................. 30

Tables

Table 4-1 Guidelines for Evaluation .................................... 4

Table 8-1 Test Methods ..................................................... 18
Table 10-1 Conditions for Chemical Resistance Testing .... 22

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February 2014 IPC J-STD-030A

Selection and Application of

Board Level Underfill Materials

1 SCOPE

This document provides users of underfill material with guidance in selecting and evaluating underfill material for assem-
bly solder joints second level interconnects. Underfill material is used to increase reliability of electronic devices by two
methods: alleviate coefficient of thermal expansion (CTE) mismatch (between the electronic package and the assembly sub-
strate) and/or increase mechanical strength. Underfill materials are also used for environmental protection, mechanical shock
or vibration, and anti-tampering uses. Materials used in underfill applications should not adversely affect device reliability
nor degrade electrical performance (e.g., ionic impurities). When correctly selected and applied, underfill material should
increase the life of the assembly solder joints.

Types of underfill materials currently available in the market include:

• Capillary Flow Underfill
– Primary UFs (Package level not within the scope of this document)
– Secondary (Board level)
• No-Flow/Fluxing Underfill
– Thermal Compression Bonding (TCB) Epoxies (not within the scope of this document)
– Non-Conductive Paste (NCP)
– Non-Conductive Film (NCF)
• Removable/Re-Workable Underfill
• Corner Bonding/Glue Bonding
• Molded Underfill (not within scope of document)
• Wafer Applied Underfill (not within scope of document)
• Vacuum Underfill (not within scope of document)

1.1 Introduction This document covers polymer based underfill materials intended for use in printed circuit assemblies
(PCA). (See Figure 1-1.)

1.2 Purpose The purpose of this document is to help in

identifying underfill materials whose properties are compat- G
ible with component assembly joints to reduce thermo
mechanical stress so that performance of the assembly is
enhanced. The additional role of underfill is protecting the A
device from environmental factors and increasing strength. D
Evaluation methods are provided in the document that are H
intended to be used for assessing underfill material perfor-
mance in specific applications as well as troubleshooting fail- B
ures. This document represents the compiled knowledge and
E
experience of the IPC Underfill Adhesives for Flip Chip
Applications Task Group. C F
IPC-030a-1-1
1.3 Definition of Requirements The word ‘‘shall’’ is used
in the text of this document wherever there is a requirement Figure 1-1 Comparison of Various Sized Array Packages
for materials, preparation, process control, or acceptance of a A. Ball Grid Array (BGA) E. 300 micron balls
soldered connection or a test method. The word ‘‘should’’ B. Chip Scale Package (CSP) F. 75 micron balls
reflects ‘‘best processing techniques’’ and is used to reflect C. Flip Chip (FP) G. 35 mm [1.38 in]
D. 760 micron balls H. 1.2x chip size
general industry practices and a suggestion for guidance only.