Solder Pastes
Technical Needs, Gaps and Solutions
The technology issues surrounding Solder Paste, 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. Solder Paste Gaps, and Today’s Technology Status with Respect to Current and Future Needs
TECHNOLOGY ISSUE | ROADMAP TIMEFRAME | |||
TODAY (2024) | 3 YEARS (2027) | 5 YEARS (2029) | 10 YEARS (2034) | |
Solder Paste | ||||
SOLDER PASTE ISSUE #1: Need high surface insulation resistance(SIR)/electronic control module (ECM)/ flux reliability for no-clean. 50 um board pad lines and spacings used today. 20 um lines and spacing are in the 3 to 5 year horizon. SIR test coupons are looking down to 200 um spacing. Current IPC SIR test methods have spacings of 300 um to 400 um | ||||
NEED |
| |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Some high SIR flux materials are available but limited. | ||||
GAP | Lack of suitable alternatives or development. Flux activators may not be evaporated during reflow (e.g., thermal quad-flat no-leads (QFN) pad). At what point will the board spacing be so small that no clean materials cannot be used and we will just use water soluble pastes? | |||
CHALLENGE | Compatibility with conformal coating/underfills/solder mask, etc. Obtaining high SIR flux materials. | |||
SOLDER PASTE ISSUE #2: Need for ultra-low residue paste to be compatible (SIR/ECM adhesion) with encapsulation materials (e.g., conformal coating, underfill, etc) which does not need to be cleaned. (similar to Issue #1) | ||||
NEED | Low amount of flux residue (how much is low amount: % reduction in residue reduction) while still maintaining good wetting and other properties in the paste?) | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Some low residue materials available. Need to reflow in higher purity Nitrogen (<100 ppm O2) (not mainstream). Typical residue amount today for regular paste is 6%. Low residue pastes the value is 2 to 3%. The higher the flux residue amount, the more sensitivity to the property of the underfill material. | ||||
GAP | Ultra-low residue paste with good wetting and reflowability in air especially with finer powder sizes (Type 5 and smaller) | |||
CHALLENGE | Balance between low residue and good wetting for this type of paste | |||
SOLDER PASTE ISSUE #3: Need excellent printing paste for low area ratios/small apertures for Type 4 solder paste | ||||
NEED | Excellent printing with low aspect ratio (AR) (<0.55-0.6) with Type 4 paste | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Use Type 5 paste with Nitrogen reflow, step down stencil, nano-coatings, printing machine update | ||||
GAP | Lack of Type 4 paste available with good printing at low AR. | |||
CHALLENGE | Better printability with Type 4 pastes. | |||
SOLDER PASTE ISSUE #4: Need development of low temperature alloys used in the solder paste | ||||
NEED | Reduced warpage, lower energy costs/usage | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
| ||||
GAP |
| |||
CHALLENGE | Low temperature alloys such as SnBi are generally brittle. Electromigration of Bi in SnBi alloys. | |||
SOLDER PASTE ISSUE #5: Need low voiding pastes during reflow | ||||
NEED | Lower voiding on BTC/QFN type components (< 20% in air convection reflow oven) | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Typically, 30-50% in air convection oven, expected to gradually reduce to 20-30% over a ten-year period. Use of vapor phase/vacuum reflow ovens to reduce voiding to less than 5%. Use higher standoff height to help to have voids to escape. Use Nitrogen (<1000 ppm 02). Profile development. Challenges with voiding around thermal vias. REACH chemical restrictions may reduce the amount of flux materials which can be used. | ||||
GAP | Need more development of low voiding pastes. | |||
CHALLENGE | Development of low voiding paste: what to change in the flu without losing other properties of the flux (e.g., wetting, pin testability, etc). | |||
SOLDER PASTE ISSUE #6: Need large process window for paste for reflow process | ||||
NEED | Survive high temperature and time with long preheat soak times. (230°/235°C to 260°C temperatures for SnAgCu) (Soak time 45 sec to 120 sec) | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Some paste materials can survive high temperatures and long soak times. Protect smaller components from excessive heat. | ||||
GAP | Development of a paste to address this wide temperature variation. | |||
CHALLENGE | Large BGAs and small components on a large thermal mass board. Cold joints on large components and flux exhaustion/vaporization on small components. Development of a paste material which is tolerant to high temperatures and long soak times which have good printing and other properties. | |||
SOLDER PASTE ISSUE #7: Need a no-refrigeration paste | ||||
NEED | Move development of no-refrigeration paste with a larger process window. Reduce logistics issue during transport and lower transport costs. Ease of storage in production/warehouse. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
There are a limited number of solder paste materials available that have a shelf life up to 12 months at room temperature. Customers ask for long shelf life but it is not a major priority compared to other properties such as printing and reflow. | ||||
GAP | Not a wide range of no refrigeration paste for all applications/alloys. Trade off with their use in terms of voiding/slump and other paste performance. | |||
CHALLENGE | Some of the materials available tend to slump. Matching performance requirements of refrigerated pastes. | |||
SOLDER PASTE ISSUE #8: Need high reliability alloy pastes (need better definition of high reliability: shock, vibration, available transfer capability (ATC), etc.) | ||||
NEED | One high reliability alloy for all reliability requirements | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
High reliability alloy pastes are available but different alloys give different performance. | ||||
GAP | Challenge that one alloy does not fit all needs. Product-dependent requirements. (TC vs vibration vs mechanical shock) | |||
CHALLENGE | - | - | - | - |
SOLDER PASTE ISSUE #9: Need no-clean paste which can be cleaned more effectively and use of more benign cleaning materials | ||||
NEED | No-clean flux residues that are more effectively cleaned with more benign materials. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Cleaning of no-clean is with solvents. Some pastes can be cleaned with more benign materials. High reliability and harsh environment segments will push for this. | ||||
GAP | Layer for no-clean residue to be removed with more benign materials. | |||
CHALLENGE | If a no-clean is susceptible to being cleaned with DI water only, then it will be a reliability issue. Development of no-clean paste which still has good overall performance and can be cleaned with more benign cleaning materials. | |||
SOLDER PASTE ISSUE #10: Need low-temperature solder paste with high SIR/ECM reliability for bottom terminated component (BTC)-type components | ||||
NEED | Higher amount of activators remaining with low temperature solder reflow profiles. Need to ensure activators are consumed and encapsulated so it does not cause a reliability issue. Review and update IPC standards to replicate BTC conditions in the field. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Low-temperature solders paste meet current SIR requirements, but SIR requirements do not account for low standoff/covered components (50 um standoff height for BTC components versus 200-300 um for BGA components)1 | ||||
GAP | Little work with SnBi paste reliability with BTC type components. Outgassing issue under part. | |||
CHALLENGE | Lack of progress in this area. Investigate different amounts and types of activators due to increased oxidation of Bi compared with Sn. | Newer BTC components designs may affect SIR results. | ||
SOLDER PASTE ISSUE #11: Need test vehicle/test method development and modelling for SIR testing of no-clean solder pastes | ||||
NEED | Smaller spacings, high and very low voltages. Low stand-off BTC components. Need modelling for SIR testing and reliability. Standardized reflow profile and atmosphere | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
| ||||
GAP | Outgassing issue under parts affecting reliability. Standards do not account for low and high voltages. | |||
CHALLENGE | Some BTC components have heights as low as 50 um. Have solder paste with limited outgassing process. | |||
SOLDER PASTE ISSUE #12: Need improved flux residue reliability after partial cleaning/spot cleaning for reflowed soldered pastes | ||||
NEED | Cleaning method for localized/spot cleaning at room temperature. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Chemicals are available for localized/spot cleaning which are expensive. Low-cost alternatives such as isopropyl alcohol (IPA) are used which may not be effective. | ||||
GAP |
| |||
CHALLENGE | How do we correlate partial cleaning with SIR reliability? | |||
SOLDER PASTE ISSUE #13: Regulatory impacts on all materials development | ||||
NEED | More transparency in understanding regulations impact. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
Some companies are asking for full disclosure (IPC 1752). EU Reach legislation which is updated every 6 months. | ||||
GAP | Need to have more impact into regulations to streamline process | |||
CHALLENGE | Many regulations that are being developed are changing. This information is not readily available from and to flux developers/formulators. Multiple questionnaires from customers require more staff at suppliers, Increased time and cost. Safety data sheet (SDS) variations in different regions. Increased requirements. | |||
SOLDER PASTE ISSUE #14: Reduction in powder sizes affecting processability | ||||
NEED | Reduced powder sides more oxidation (Type 5 and higher types). Flux needs to remove more oxidation. Improved slumping performance, cleanability, reduced solder balling, bridging. Improved shelf life. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
For Printing: Type 3 and 4 and down to Type 5 and 6. For Jetting: Type 6 and 7 are available and even down to Type 8. Use of Nitrogen increasing. Increased cost with smaller powder sizes. AR needs. | ||||
GAP | Development of smaller powder sizes in paste with good wetting/ solderability. Improved hot slump performance. | |||
CHALLENGE | Increase solder wetting with smaller powder sizes without solder paste negatively impacting reliability. | |||
SOLDER PASTE ISSUE #15: Removal of solder paste flux build up in reflow equipment- flux management (This content is covered in the INEMI Surface Mount Technology Printing and Reflow group roadmap. Refer to this roadmap section for further details.) | ||||
SOLDER PASTE ISSUE #16: Soldering to hard-to-solder materials (aluminum heat sinks/plates) and copper plates (high-heat sink material) and RF Shields (Ni, Ni/Al) | ||||
NEED | Increased solderability of difficult to materials with current low activity no-clean solder pastes. | |||
CURRENT TECHNOLOGY STATUS | Solutions need optimization | |||
| ||||
GAP | Lack of solder pastes developed which are low activity which are capable of removing oxides (e.g., solder alloy, Al, Cu, Ni, etc.) at normal soldering temperatures. | |||
CHALLENGE | Difficult to solder to. Have increased flux activity which could be a reliability issue if no-clean. | |||
SOLDER PASTE: ISSUE #17: High current carrying capacity (HCCC) (6 to 8 amps, 3KA/cm2 to 4KA/cm2) solders, which exhibit minimal electromigration and have higher conductivity than current SnAgCu, SnPb and SnBi solders. | ||||
NEED | (1) HCCC solder which exhibits minimal resistance and microstructural changes with high constant or pulsed (current on and off) current. (2) Consensus on Electromigration Test Methodology applicable to second level interconnects (SLIs) | |||
CURRENT TECHNOLOGY STATUS | Solutions not known | |||
Sn-Ag-Cu (SAC) solder has moderate current carrying capacity with microstructural changes resulting in opens after a moderate length of time under 4 to 6 A/cm2 current densities. BiSn solder has low current carrying capacity (<4 A/cm2) due to bismuth segregation at one end of the solder joint under high current densities. | ||||
GAP | Solder with conductivity in the 25-20 % Industrial Automation and Control System (IACS) range with minimal microstructural changes and resistance increase under high (constant and pulsed) current exposure, (Copper- 100% IACS, Solder- 15, Bi metal-3). | |||
CHALLENGE |
| |||
SOLDER PASTE: ISSUE #18: Solder paste for Warm Assembly (<140°C peak reflow temperature and >100°C peak) with re-melt temperature above temperatures used in the field. | ||||
NEED | Driven by increased warpage of flip chip BGAs (FCBGAs) and thinner PCBs, heat sensitive components (e.g., co-packaged optics (CPOs) and sensors also a factor after assembly |
| ||
CURRENT TECHNOLOGY STATUS | Solutions not known | |||
Ultra Low Temperature solders exist such as those based on Sn-In (Mp 118°C) or Sn-Ga, but these solders have melting points very close to use temperatures of the electronic products in the field (Thomologous effect). | ||||
GAP | Need for a range of WA temperature solder materials that can be used for reflow soldering assembly of components below 140°C temperature, but which re-melt at temperatures above ~170°C, for example. | |||
CHALLENGE | Identification of of transient liquid-phase sintering (TLPS)-like and supercooled metallic powder particulate technology materials for preliminary assessment in board assembly. | Development and testing of TLPS-like and supercooled metallic powder particulate technologies to meet assembly yield requirements for large, high-dynamic warpage packages and assembly temperature below optical and photonic components temperature exposure limit. |
Approaches to address Needs, Gaps and Challenges
Table 2 considers approaches to address Solder Paste 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. Solder Paste Potential Solutions
TECHNOLOGY ISSUE | EXPECTED TRL LEVEL* | ||||
Solder Paste Materials | POTENTIAL SOLUTIONS | TODAY (2024) | 3 (2027) | 5 (2029) | 10 |
SOLDER PASTE MATERIALS ISSUE #1: | Flux development | 4 | 5 | 7 | 8 |
SOLDER PASTE MATERIALS ISSUE #2: | Flux development | 4 | 5 | 7 | 8 |
SOLDER PASTE MATERIALS ISSUE #3: | Type 4 paste printing development | 7 | 7 | 7 | 9 |
SOLDER PASTE MATERIALS ISSUE #4: | Addition of dopant elements (optimizing combination and percentage by weight (wt%)) | 5 | 6 | 7 | 8 |
SOLDER PASTE MATERIALS ISSUE #5: | Lead-free SnAgCu paste development for < 20% voiding | 3 | 4 | 5 | 6 |
SOLDER PASTE MATERIALS ISSUE #6: | Paste development | 4 | 5 | 6 | 7 |
SOLDER PASTE MATERIALS ISSUE #7: | Paste development | 5 | 6 | 7 | 8 |
SOLDER PASTE MATERIALS ISSUE #8: | Industry definition of high reliability by product type (company versus industry standard differences- shock, vibration, ATC) | 5 | 6 | 7 | 7 |
SOLDER PASTE MATERIALS ISSUE #9: | Paste development | 5 | 6 | 7 | 7 |
SOLDER PASTE MATERIALS ISSUE #10: | Paste development | 5 | 6 | 7 | 7 |
SOLDER PASTE MATERIALS ISSUE #11: | Test vehicle development (Industry standardization) | 5 | 5 | 7 | 8 |
Test method development | 5 | 5 | 7 | 8 | |
Modelling for SIR testing and reliability | 2 | 4 | 6 | 8 | |
SOLDER PASTE MATERIALS ISSUE #12: | Development of cleaning method for localized /spot cleaning at room temperature to remove flux residue. | 4 | 5 | 6 | 7 |
Development of low-cost chemicals for localized spot cleaning. | 4 | 5 | 6 | 7 | |
Development of fluxes to meet reliability requirements without sufficient heating—Define pre-condition (e.g., 24 hours at room temperature) and define component spacings/ voltage differential | 5 | 6 | 6 | 7 | |
Development of benign flux residue even after partial cleaning | 5 | 6 | 6 | 7 | |
Understanding the correlation of partial cleaning of flux residue with SIR reliability (Modelling) | 2 | 4 | 6 | 8 | |
SOLDER PASTE MATERIALS ISSUE #13: | Transparency in understanding regulations impact and timelines | 4 | 5 | 6 | 7 |
Streamline regulation process | 2 | 3 | 4 | 5 | |
Feedback from industry into regulation process | 2 | 3 | 4 | 5 | |
SOLDER PASTE MATERIALS ISSUE #14: | Flux development | 6 | 7 | 7 | 7 |
SOLDER PASTE MATERIALS ISSUE #15: | (This content is covered in the INEMI Surface Mount Technology Printing and Reflow group roadmap. Refer to this roadmap section for further details.) | ||||
SOLDER PASTE MATERIALS ISSUE #16: | Flux development ((Cu) | 6 | 7 | 7 | 7 |
Flux development (Al) | 5 | 6 | 6 | 7 | |
Flux development (Ni) | 6 | 6 | 7 | 7 | |
SOLDER PASTE MATERIALS ISSUE #17: | Development of novel metallurgies for solder paste particles particularly containing highly conductive elements such as copper | 2 | 5 | 7 | 9 |
SOLDER PASTE MATERIALS ISSUE #18: | Development of novel solder metallurgies and reflow / rework processes | 2 | 5 | 7 | 9 |
Conclusions
Need for high SIR/ECM/ flux reliability for no-clean for smaller spacings (< or = 200 um)
Need for excellent printing paste for low area ratios/small apertures for Type 4 solder paste
Development of low-temperature alloys used in the solder paste
Low voiding pastes during reflow
High reliability alloy pastes (with a better definition of high reliability: shock, vibration, available transfer capability (ATC)
Regulatory impacts on all materials development with more transparency in understanding regulation impact and timelines
Reduction in powder sizes (Type 5 and higher) in solder paste and its effect on processability
References
M Bixenman, M. McMeen and L. Diamond, Requirements for Soldering Fluxes Research using the B-53 Test Board, IPC APEX EXPO 2023.
Board Assembly Acronyms
Return to Assembly Materials.