Assembly Materials

Introduction

Assembly Materials technology is a critical part of the electronic assembly process. Technology issues and solutions have been identified by industry experts comprised of assembly materials manufacturers and engineers who are involved in this area on a daily basis. A total of 17 issues are reviewed in the area of solder paste, 7 issues for TIMs, 6 issues for conformal coatings, 6 issues for underfills, 4 issues for encapsulant/potting materials, 3 issues for wave solder materials and 3 issues for rework solder materials. These topics are detailed in the following sub-sections:

• Solder Pastes,

• Thermal Interface Materials (TIMs),

• Conformal Coatings,

• Underfills,

• Encapsulant/Potting Materials,

• Wave Solder Materials and

• Rework Solder Materials.

Technical Needs, Gaps and Solutions

The technology issues surrounding Board Assembly Materials listed above and the associated needs, technology status of those needs, as well as gaps and challenges to overcome, are summarized in each sub-section. The time period considered is from 2024 to 2034.

Technology Status Legend

For each need, the status of today’s technology is indicated by label and color as follows:

Approaches to address Needs, Gaps and Challenges

Each of the Board Assembly sub-section considers approaches to address the above needs and challenges. The evolution of these is projected out over a 10-year timeframe using technology readiness levels (TRLs).

Conclusions

Assembly materials development continues to be a challenging area in electronics assembly operations due to the increased miniaturization and densification of components and assemblies. Technology issues have been identified and projected by industry experts who are investigating assembly materials used in product on a daily basis. Key issues are listed below for each Assembly Materials roadmap topic:

Solder Paste

1. Need for high SIR/ECM/ flux reliability for no-clean for smaller spacings (< or = 200 um)

2. Need for excellent printing paste for low area ratios/small apertures for Type 4 solder paste

3. Development of low-temperature alloys used in the solder paste

4. Low voiding pastes during reflow

5. High reliability alloy pastes (with a better definition of high reliability: shock, vibration, available transfer capability (ATC)

6. Regulatory impacts on all materials development with more transparency in understanding regulation impact and timelines

7. Reduction in powder sizes (Type 5 and higher) in solder paste and its effect on processability

Thermal Interface Materials (TIMs)

1. Addressing voiding to reduce thermal impedance/resistance in solder TIMs

2. Addressing voiding in other TIMs (non-metal TIMs) (e.g., thermal greases, gels, pads, TC adhesives) (Voiding is more of an issue with adhesives.)

3. Bleeding of TIMs (e.g., gel and pad type materials- silicones and urethanes) (TIM 2 and TIM 0 materials)

4. TIM pump-out/bleed-out/dry-out

Conformal Coatings

1. Need more development and application of nano-coatings to account for miniaturization trends (environmentally friendly, sustainable coatings)

2. Need non-fluorinated high temperature conformal coatings (PFAS)

3. Need better coverage of conformal coating (for low coating thicknesses) (application and material related issues)

Underfills

1. Reworkability with high TC (mainly for thermal cycling) and high SIR reliability

2. High reliability pre-applied or tight KOZ underfills for high package densities (Underfill can wick into adjacent components.)

Encapsulants/ Potting Materials for Board Level Assembly

1. Increased thermal conductivity while maintaining good flow/filling (TC > 2.0W/m-k)

2. Development of antimony (Sb) and halogenated free flame retardants for encapsulants/potting

3. Balancing CTE needs with modulus needs for potting materials

Wave Solder Materials

1. Reduction in the generation of solder dross especially with low melting temperature Bismuth-containing lead-free alloys

2. Improving SIR reliability of wave solder flux after soldering

Rework Solder Materials

1. Development of low-temperature, high bismuth solder containing flux cored wire

2. Improving rework flux SIR reliability after rework soldering

It is important to understand that as designs produce assemblies with miniaturized components with tighter component spacings and with the advent of larger components, the challenges for assembly materials are increasing and will increase in the future. The assembly materials suppliers continue to research equipment, materials, designs and methods to address the challenges faced in this area.

Board Assembly Acronyms

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