IEC TR 62878-2-8:2021

Device embedding assembly technology - Part 2-8: Guidelines - Warpage control of active device embedded substrate

IEC TR 62878-2-8:2021(E) describes a warpage control of active device embedded substrate along with parameters for determining warpage, which are useful during package assembly. Warpage results are explained using warpage driving force, resistance and neutral axis, for typical die embedded substrate, where the discrete active dies are placed in the core of substrate and interconnected to the substrate by direct Cu bonding. The same principles are applicable in other device embedded substrates. Even though the detailed structure of other device embedded substrates might be different, the origin and determination of the parameters of warpage are the same and thus the purpose of this report is to help engineers improve the warpage behaviours of their products by applying this principle.

General Information

• Status: Published
• Publication Date: 06-Jul-2021
• ICS: 31.180 - Printed circuits and boards
• ICS: 31.190 - Electronic component assemblies
• Technical Committee: TC 91 - Electronics assembly technology
• Drafting Committee: WG 6 - TC 91/WG 6
• Current Stage: PPUB - Publication issued
• Start Date: 07-Jul-2021
• Completion Date: 26-Jul-2021

Overview

IEC TR 62878-2-8:2021 - "Device embedding assembly technology - Part 2-8: Guidelines - Warpage control of active device embedded substrate" provides practical guidance for understanding and controlling warpage in active device embedded substrates. The report explains warpage origins using the concepts of warpage driving force, warpage resistance and neutral axis, and describes the main parameters (CTE mismatch, layer geometry, die thickness, Cu patterning and process history) that determine warpage behaviour during thermal cycles experienced in package assembly.

Key Topics

• Warpage fundamentals
  • Definition of warpage for package-to-board assembly and its impact on solder joint integrity.
  • Relationship W ∝ Δα ΔT (warpage proportional to CTE difference and temperature change).
• Driving force vs. resistance
  • Driving force: CTE mismatch among die, dielectrics, metal layers and solder.
  • Resistance: flexural rigidity (E·I) of the stack - strongly influenced by layer thickness and geometry (warpage ∝ 1/h^3 for beam-like panels).
• Neutral axis
  • Role of the neutral axis (z-axis balance of CTE/stiffness) in determining warpage direction and magnitude.
  • How shifting the neutral axis changes convex/concave warpage across temperatures.
• Design levers for mitigation
  • Material selection and CTE balancing.
  • Adjusting die thickness and die-to-panel area ratio.
  • Use of patterned or dummy Cu over die locations to balance stiffness and reduce CTE mismatch effects.
  • Emphasis on experimental verification and simulation for low-rigidity designs.
• Practical measurement & simulation focus
  • Use of measured vs. simulated warpage comparisons for validation of mitigation strategies.

Applications

IEC TR 62878-2-8 is targeted to professionals and teams responsible for device-embedding and package assembly, including:

• Package and substrate designers developing die-embedded substrates for mobile and compact electronics.
• Assembly and process engineers managing reflow, soldering and board mounting where warpage can cause open/short joints.
• Reliability engineers and test labs assessing thermo-mechanical performance and failure risk.
• CAE/simulation analysts modeling thermo-mechanical warpage and validating mitigation measures (dummy Cu, layer stack changes, die thickness). Use cases include BGA-like packages, embedded die substrates for mobile devices, and any assembly where warpage during heating/cooling influences solder joint formation.

Related Standards

• Normative reference: IEC 60194 (Printed boards design, manufacture and assembly - Vocabulary).
• Part of the IEC 62878 series: see the IEC webstore for other parts in the "Device embedding assembly technology" family.

Keywords: IEC TR 62878-2-8, warpage control, device embedding, active device embedded substrate, warpage driving force, warpage resistance, neutral axis, CTE mismatch, flexural rigidity, dummy Cu, die thickness.

Standards Content (Sample)

IEC TR 62878-2-8 ®
Edition 1.0 2021-07
TECHNICAL
REPORT
colour
inside
Device embedding assembly technology –
Part 2-8: Guidelines – Warpage control of active device embedded substrate
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IEC TR 62878-2-8 ®
Edition 1.0 2021-07
TECHNICAL
REPORT
colour
inside
Device embedding assembly technology –

Part 2-8: Guidelines – Warpage control of active device embedded substrate

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.180; 31.190 ISBN 978-2-8322-9953-1

– 2 – IEC TR 62878-2-8:2021 © IEC 2021
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Warpage driving force and resistance . 6
4.1 General . 6
4.2 Warpage driving force . 6
4.3 Warpage resistance . 6
4.4 Determining parameters . 7
5 Guideline for warpage of active device embedded substrate . 9
5.1 General . 9
5.2 Rigidity . 9
5.3 Neutral axis . 9
5.4 Typical example of low rigidity case . 10
5.5 Typical example of high rigidity case . 11
6 Conclusion . 13
Bibliography . 14

Figure 1 – Warpage behaviour of device embedded substrate during heating and
cooling . 6
Figure 2 – Relationship between warpage and rigidity . 7
Figure 3 – Parameters determining warpage . 7
Figure 4 – Effects of dummy Cu design on warpage . 8
Figure 5 – Neutral axis of device embedded substrate . 9
Figure 6 – Warpage behaviour of active device embedded substrate during heating
and cooling . 10
Figure 7 – Measured and simulated warpage results of die embedded substrates with
low rigidity . 11
Figure 8 – Structure of die embedded package with high rigidity . 12
Figure 9 – Simulated results on effect of die thickness on die embedded package
warpage . 12

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DEVICE EMBEDDING ASSEMBLY TECHNOLOGY –

Part 2-8: Guidelines –
Warpage control of active device embedded substrate

FOREWORD
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IEC TR 62878-2-8, which is a technical report, has been prepared by IEC technical committee
91: Electronics assembly technology.
The text of this Technical Report is based on the following documents:
Draft Report on voting
91/1649/DTR 91/1721/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.

– 4 – IEC TR 62878-2-8:2021 © IEC 2021
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assembly technology, can be found on the IEC website.
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DEVICE EMBEDDING ASSEMBLY TECHNOLOGY –

Part 2-8: Guidel
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