Underfills
Technical Needs, Gaps and Solutions
This section covers technology issues surrounding Underfills, the associated needs, technology status of those needs, as well as gaps and challenges to overcome, are summarized below in Table 1. The time period considered is from 2024 to 2034. Assessments of to address these gaps and challenges is presented in Table 2 as a set of potential solutions for each set of issues.
Technology Status Legend
For each need, the status of today’s technology is indicated by label and color as follows:
In-table color + label key | Description of Technology Status |
|---|---|
Solutions not known | Solutions not known at this time |
Solutions need optimization | Current solutions need optimization |
Solutions deployed or known | Solutions deployed or known today |
Not determined | TBD |
Table 1. Underfills Gaps, and Today’s Technology Status with Respect to Current and Future Needs
TECHNOLOGY ISSUE | ROADMAP TIMEFRAME | |||
Underfills | ||||
TODAY (2024) | 3 YEARS (2027) | 5 YEARS (2029) | 10 YEARS (2034) | |
UNDERFILL ISSUE #1: Reworkability with high TC (mainly thermal cycling) and high SIR reliability | ||||
NEED | Development of reworkable underfill with high reliability. | Right to repair EU and global initiative dictating reworkability of higher reliability applications (consumer, automotive and industrial customer). Temperature ranges are expanding, e.g., -25 to 85°C to -40 to 125°C). | ||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | Solutions need optimization | ||
Reworkable underfills are also a challenge to rework. Most products use non-reworkable underfill that passes reliability requirements. | ||||
GAP | Lack of development of fillers and polymers in underfills. Novel polymers for reworkability | |||
CHALLENGE | Balancing reliability and reworkability. Fillers added to improve reliability and polymers used in underfill also tend to inhibit reworkability. | |||
UNDERFILL ISSUE #2: High reliability underfills highly accelerated stress testing (HAST) (especially thermal cycling- functionality), reflowability (reliability of underfill after multiple reflows (e.g., daughter card onto a motherboard)) | ||||
NEED | Need to have underfills which pass from 3X to 10x lead-free (LF) reflow (260°C peak). | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Some 2nd level new underfills typically pass 3x LF reflow with flux residues. | ||||
GAP | Lack of available underfills with extended reflow capability beyond 3x reflow. | |||
CHALLENGE | After thermal cycling, more likelihood of cracking in solder, extruded joints. | |||
UNDERFILL ISSUE #3: Thermally conductive underfill. TC > 2-3 W/m.K with good flowability (Normal underfill Have TC of 0.5-0.6 W/m.K) | ||||
NEED | 2-3 W/m.K underfill | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Some available up to 1.2 W/m.K | ||||
GAP | As TC increases, the flowability reduces. | |||
CHALLENGE | Balance between TC and flowability. Limited on how much amount and type of material you can place under the part. Cost of these materials. | |||
UNDERFILL ISSUE #4: LTS compatibility- Low temperature (< 120°C) cure of underfill for SnBi solder alloys (MP: 138°C-140°C) (warpage and energy related to move to SnBi) | ||||
NEED | Need 120°C cure for underfill in less in 15 mins | |||
CURRENT TECHNOLOGY STATUS | Solutions deployed or known. | |||
Some materials available. Wider range of products may be needed. | ||||
GAP | Lower curing time at lower cure temperature | |||
CHALLENGE | Formulating the current material system without compromising other properties (reliability, shelf life/ work life) | |||
UNDERFILL ISSUE #5: High reliability pre-applied or tight Keep Out Zone (KOZ) underfills for high package densities (underfill can wick into adjacent components) | ||||
NEED | Non wicking underfills. Need material to flow and then stop. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Pre-applied material or film material but challenges such as conductivity and voiding can be an issue. | ||||
GAP | Lack of developed material with appropriate shear properties. | |||
CHALLENGE | Development of materials with appropriate shear properties. | |||
UNDERFILL ISSUE #6: Compatibility of underfill with flux in paste | ||||
NEED | More compatibility (SIR, ECM, delamination, reliability) | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Testing to evaluate compatibility and choose a specific combination. Dependent on solder paste with materials in the underfill. Clean solder paste fluxes after reflow as needed to avoid this issue but not an ideal situation. Driver on cleaning flux residue is reliability application dependent. | ||||
GAP | Lack of a clearer idea of compatibility between solder paste and underfill (very material dependent). Some underfill chemistries are more compatible than others and this is also the case with soldering materials. | |||
CHALLENGE |
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Approaches to address Needs, Gaps and Challenges
Table 2 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).
In-table color key | Range of Technology Readiness Levels | Description |
|---|---|---|
2 | TRL: 1 to 4 | Levels involving research |
6 | TRL: 5 to 7 | Levels involving development |
9 | TRL: 8 to 9 | Levels involving deployment |
Table 2. Underfills Potential Solutions
TECHNOLOGY ISSUE | EXPECTED TRL LEVEL* | ||||
Underfills | POTENTIAL SOLUTIONS | TODAY (2024) | 3 (2027) | 5 (2029) | 10 |
UNDERFILL ISSUE #1: | Formulation optimization and novel chemistries for improved TC and SIR | 5 | 6 | 7 | 8 |
UNDERFILL ISSUE #2: | Formulation optimization and novel chemistry. | 6 | 7 | 8 | 8 |
UNDERFILL ISSUE #3: | Development of novel chemistry and formulation optimization | 6 | 7 | 8 | 8 |
UNDERFILL ISSUE #4: | Formulation optimization | 7 | 8 | 8 | 8 |
UNDERFILL ISSUE #5: | Formulation optimization and novel chemistry. | 4 | 5 | 7 | 7 |
UNDERFILL ISSUE #6: | Development of novel chemistry and formulation optimization | 5 | 6 | 6 | 7 |
Conclusions
Reworkability with high TC (mainly for thermal cycling) and high SIR reliability
High reliability pre-applied or tight KOZ underfills for high package densities (Underfill can wick into adjacent components.)
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