The Development of Active Lead-free Solders [R&D partner & technology search case]

(I) Request, objective and implementation in short

1. The need: LAB GmbH, the client company, requires active solders in combination with metallization of non-metallic materials (for replacement of conventional solders) efficient at or above 250°C. The LAB GmbH contacted Active Solders Ltd, an Austrian technical university spin-off.
2. Available technology: Active Solders Ltd has active lead-free solder technology efficient in the 150–240°C range.
3. Request: (a) Active Solders Ltd seeks for potential Partners operating in R&D of active solders to satisfy the LAB GmbH's need; (b) Active Solders Ltd wants to know what lead-free solder alloys are used at higher temperatures.
4. Compliance: The active solders must be compliant with the Directive 2011/65 / EU RoHS.

(II) Operationalization

BACKGROUND KNOWLEDGE

Q1. What was the “conventional solder”?
Q2. What is “the primary lead-free solder” and who is(are) the applicant(s)?
Q3. How melting temperature of a solder and peak solder’s application temperature (e.g., reflow oven) are connected?
Q4. What is “active solder” and why is it needed?
Q5. What are the restricted substances according to the Directive 2011/65 / EU RoHS?

Q6. The search for potential Partners: Which organizations perform R&D in the field of (active) solders? Specifically, two following requirements must be satisfied:
    a) non-metallic materials soldering.
    b) temperature range: equal to 250°C or above.
Q7. What are the (lead-free) solder alloys (i.e., technical solutions) being used by potential Partners identified?
Q8. What are the respective organizations that own relevant patents, patent applications, utility models, etc.?
Q9. Which of these patents are in force?
Advise for the potential Partner depending on retrieved results (questions Q1–9 above).

(III) Execution of the search

Non-Patent Literature (NPL) search results & Analysis:

Q1: The lead-based, tin-lead (SnPb), alloy was the conventional solder for more than 50 years.

Q2: Since 2006, after EU’s Restriction of Hazardous Substances (RoHS) Directive implementation, the primary lead-free solder for attaching electronic devices to printed circuit boards (PCBs) has been the Sn_3.0Ag_0.5Cu (i.e., Sn-based alloy, containing 3.0 wt.% of silver and 0.5 wt.% copper; melting temp. 217°C), or SAC305 alloy, covered by JP3027441B2 patent owned by SENJU METAL INDUSTRY CO [JP]. SAC305 alloy replaced the high-Ag eutectic alloy (Sn_4.7Ag_1.7Cu) covered by US6231691B1 patent owned by UNIV IOWA STATE RES FOUND INC [US]. In addition, a less expensive SnCu eutectic (melting temp. typically 227°C) has gained a substantial market share as well.

Q3: Usually, the soldering process temperature is higher than the solder melting temperature. For instance, the SAC305 solder paste melting temperature is 217°C, whereas the peak reflow temperature in the oven can easily be 242°C.

Q4: Ceramics and ceramic surfaces, graphite, and alloys (e.g., Ti, Al, Mg, etc.) that easily form oxide passivation layer via natural oxidation are not wetted by common solders. Active solders contain active filler metals (Ti, Mg, rare earth, etc.) containing active elements capable of joining the nonwetting materials at low temperatures (typically < 250°C) in the air.

Q5: Directive 2011/65 / EU RoHS: Restricted substances referred to in Article 4(1) and maximum concentration values tolerated by weight in homogeneous materials:
    Lead (0.1 %)
    Mercury (0.1 %)
    Cadmium (0.01 %)
    Hexavalent chromium (0.1 %)
    Polybrominated biphenyls (PBB) (0.1 %)
    Polybrominated diphenyl ethers (PBDE) (0.1 %)

Applications exempted from the restriction in Article 4(1):
7(a) Lead in high melting temperature type solders (i.e., lead-based alloys containing 85 % by weight or more lead).

Patent Literature (PL) search & Analysis:

STEP 1

Advanced patent search yielded 109 hits (patent families). Preliminary analysis of 109 hits identified a single relevant patent document: US11581239B2 Lead-free solder paste as thermal interface material by INDIUM CORP [US]:

US11581239B2 Claims:

Claim 1: “A method, comprising: applying a solder paste on a non-metallized surface of a heat generating device and on a non-metallized surface of a heat transferring device to form an assembly”; and

reflow soldering the assembly to form a solder composite that, provides a thermal interface between the heat generating device and the heat transferring device,

wherein:

the solder paste comprises: a solder powder; particles having a higher melting temperature than a soldering temperature of the solder paste; and epoxy flux,

the solder paste has a volume ratio of the solder powder to the particles that is 5:1 to 2:1,

the particles comprise a copper or copper-alloy powder,

the solder powder comprises an alloy including Sn, Ag, and Cu,

during reflow, the solder powder melts and wets to the copper or copper-alloy powder to form a CuSn intermetallic compound, and

a low melting temperature phase of the alloy remains in the solder composite."

Claim 2: “The method of claim 1, wherein reflow soldering the assembly comprises reflow soldering the assembly at a peak temperature of 250°C or less.”

Further analysis of US11581239B2 patent revealed two major Section B subgroups and the classification search was then performed yielding 12764 hits (patent families).

STEP 2

Subsequently, to refine the results, the smart search was performed resulting in 35 hits (patent families), thus increasing the specificity of the search 365-fold (12764 → 35).

The obtained thirty-five hits are represented in Table (below):

(IV) Evaluation/conclusion

In the Table above, two types of cell shading are used.

First — golden shading — indicates that the search has been relevant by identifying the organizations with the major impact on the soldering field and market: The University of Iowa [US] and Senju Metal Industry Corporation [JP]. The fact that the smart search yielded these organizations indicates the relevancy of the results. However, the US10266925B2 patent deals with joining of at least one metallic and a non-metallic material, which makes it not relevant for the objectives pursued here. The patent family (KR101965037B1, EP2891538B1, JP5780365B2, US9487846B2, CN104755221B) by Senju, on the other hand, deals with non-metals joining and is hence relevant to the objectives of the current R&D Partner Search Case. However, Senju Metal Industry Corporation [JP] is a large organization that, most likely, won’t develop for a small Austrian spinoff [strategic misalignment] and even if such a thing would hypothetically happen, then the spinoff wouldn’t be able to afford it. It is possible that the solution required by LAB GmbH can be directly purchased via SMIC Senju Metal Industry Co., Ltd. website.

Second — green shading — indicates the relevant organizations found, which correspond to the objectives of the current R&D Partner Search Case. Specifically, these are the organizations that have the patents/patent applications specified in the Table above, which describe the: non-metallic materials soldering in the temperature range ≥ 250°C.

Green-shaded organizations are the potential Partners sought by Active Solders Ltd and the details associated with their technologies, i.e., the answers to Q6 – Q10 (for details see the “Operationalization” above).

We will now analyze the organizations shaded in green:

First, Slovenská Technická Univerzita v Bratislave [SK], a Slovakian university, very active in soldering field: an additional smart search yields 23 hits, which are mostly Slovakian utility models. For instance, SK9660Y1’s abstract says: “The active soldering alloy on the basis of tin for soldering metallic, non-metallic, ceramic and composite materials at the temperature from 225 to 280°C comprises scandium in amount from 0.1 to 3 % by weight.” Thus, geographically close Slovenská Technická Univerzita v Bratislave [SK] is the potential Partner #1 for Active Solders Ltd. In addition, due to the locality of the utility models and patents, Active Solders Ltd might consider using these R&D results freely in Austria.

Second, Materials Resources Internat [US] is a strange formation (only 4 patent families) and is seen at least twice in the Table above. However, on a closer inspection it becomes evident that the actual intellectual property creator is the Euromat GmbH [DE], which has at least 32 patent families. Interestingly, one of the inventors had been associated with Austria and another with Germany – thus, an opportunity for the Austrian spinoff to hire the expert in the field. The motto of the German company is: “Consulting development joining, soldering/brazing and coating service”. Hence, German Euromat GmbH [DE] is the potential Partner #2 for Active Solders Ltd.

CA2243762C (Materials Resources Internat [US]; Euromat GmbH [DE]): Claims:

“31. The method according to claim 28 wherein the solder alloy is applied at a solder temperature of at most 500°C.

"32. The method according to claim 31 wherein the solder alloy is applied at a solder temperature of 200 – 450°C."

"34. The method according to claim 28 wherein the solder joint surface of at least one of the workpieces to be joined is a nonmetallic material."

US7041180B2 (Materials Resources Internat [US]; Euromat GmbH [DE]): Claims:

“1. A method for joining workpieces by soldering, the method comprising the steps of:

providing a solder alloy consisting essentially of 1-10% by weight of an element or a mixture of elements selected from the group consisting of titanium, zirconium, hafnium, vanadium niobium and tantalum, 0.01-1% by weight of an element or a mixture of elements selected from the group of lanthanides (rare earths), 0.5-10% by weight of an element or a mixture of elements selected from the group consisting of silver, copper and indium, 0.01-1% by weight of gallium, and a remainder of tin, lead or of a mixture of tin and lead; ...

4. The method according to claim 1 wherein the solder alloy is applied at a solder temperature of at most 500°C.

5. The method according to claim 4 wherein the solder alloy is applied at a solder temperature of 200-450°C.

7. The method according to claim 1 wherein the solder joint surface of at least one of the workpieces to be joined is a nonmetallic material.”

Third, the Indium Corp [US] and the relevant patent document US11581239B2 has already been analyzed above (starting with the first paragraph of the “Patent Literature (PL) search & Analysis” section). Indium Corporation [US] has a patent portfolio consisting of at least 100 patent families. Their motto is: “We research, develop, and manufacture advanced electronics assembly materials solutions to the challenges of today, tomorrow, and the future.” US Indium Corporation specializes in the R&D of Solders and would be ideal potential Partner #3 for Active Solders Ltd, however, Indium Corp is a large enterprise with a several hundred millions revenue, which makes partnership less probable.

Fourth, Fry Metals Inc [US] US7663242B2 patent and most likely all other patents were assigned to (acquired by) the Alpha Assembly Solutions Inc. [US], which has at least 60 patent families and have recently filed patent applications on soldering. The assignment of US7663242B2 patent (and the remaining family members) and other solder-specific families by Alpha Assembly Solutions Inc [US] indicates the importance of soldering R&D for the latter. Thus, Alpha Assembly Solutions Inc [US] is the potential Partner #4 for Active Solders Ltd.

US7663242B2 Claims:

“1. ... wherein the thermal interface material has a reflow temperature less than about 250°C.

27. The thermal interface material of claim 1 wherein the solder component wets metallic and non-metallic surfaces without extrinsic fluxing, the solder component comprising a bonding component selected from the group consisting of indium and indium-tin alloys, and further comprising an intrinsic oxygen getter selected from the group consisting of alkali metals, alkaline-earth metals, refractory metals, rare earth metals, zinc, and mixtures and alloys thereof.”