ACEA/JAMA/KAMA/CLEPA et. al. request the exemption of: Lead in solder for large power semiconductor assemblies

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1 No Questions Answers 1 Wording of the exemption Materials and components: Lead in solder for large (> 1cm 2 ) power semiconductor assembly Scope and review date of the exemption No expiry date can be defined until a technical solution is determined. (Review after 2015) 2 What is the application in which the substance/compound is used for and what is its specific technical function? Application is the die soldering of Silicon chips (Si chips) of large size, having about 1 cm 2 of surface area or more, to lead frames. Insulated Gate Bipolar Transistors (IGBT) are Silicone semiconductor chips; they are the main active component in power modules for Hybrid Electric Vehicles (HEV) and Electric Vehicles (EV). The semiconductor chips are converters that control the electric voltage and current between battery and the electric drive motor / alternator of a vehicle. 3 What is the specific (technical) function of the substance/compound in this application? The solder used to join the Si chip to the lead frame is containing Lead. The Lead containing Tin-Lead solder (SnPb solder) provides thermal conductivity from the semiconductor chip, over the heat spreader, to the metal lead frame. The design can involve an intermediate heat spreader, as seen in the figure. Fig 3.1 Situation of the application High melting temp solder Si chip Heat spreader lead frame Concerned solder Following technical constraints and requirements are necessary for the safe function of the soldering joint: -The thermal conductivity of all components must be as high as possible, and uniform over the complete chip surface, to ensure the fast flow of thermal energy from the chip to the lead frame. - No appearance of cracks within the soldering phase. - The bond to be stable against cyclic loads

2 4 Please justify why this application falls under the scope of the ELV or the RoHS Directive (e.g. is it a finished product? is it a fixed installation? What category of the WEEE Directive does it belong to?). 5 What is the amount (in absolute number and in percentage by weight) of the substance/compound in: i) the homogeneous material ii) the application and iii) total EU annually for relevant applications? 6 Please justify your contribution according to Article 4 (2) (b) (ii) ELV or according to Article 5 (1) (b) RoHS Directive whereas: 7 Justification according to technical and scientific progress Any automotive application falls under the EU ELV directive. As these devices are designed primarily for use in vehicles [ ] the ELV Directive applies. (Frequently Asked Questions on Directive 2002/95/EC on the Restriction of the Use of certain Hazardous Substances in Electrical and Electronic Equipment (RoHS) and Directive 2002/96/EC on Waste Electrical and Electronic Equipment (WEEE)). In contrast to typical consumer electronics which is lead-free under ROHS regulation the requirements for automotive electronics are significantly more demanding. The automotive applications are not covered by any category of the WEEE directive. Calculation for SnPb solder. Example data of current HEV power module: i) SnPb solder containing 50% Pb (w/w). ii) About 0.64 g solder per Si chip, equalling to 23.2 g of SnPb solder per power module (36 chips per module, one module per car) Result: 11.6 g pure Pb per car iii) Assuming a sales of cars: 0,12 t Pb per year. mention: for hybrid HEV + EV There is no known alternative to the lead in solder for large power semiconductor assemblies. It is therefore necessary to apply for an exemption for lead in solder for large power semiconductor assemblies in relation to entry 8a) of Annex II to the ELV 2000/53/EC. 1) For the soldering process: It is necessary to melt the solder between the heat spreader and the lead frame at a temperature lower than the melting temperature of the solder used for the Si chip soldering (around 300 C). 2) For the performance of the soldered joint: Cracks and voids have a detrimental influence on the bond reliability and the heat dissipation of the soldered transistor chips. These chips, Insulated Gate Bipolar Transistor (IGBT) type components, are during the operation subjected to high currents, which result in high thermal loads. As the application, high-density power modules for HEV and EV, are newly developed, there is yet no practical experience available on the amount and magnitude of real-life load cycles, and no experience on the fatigue behaviour of the solder and the soldered components. To allow an assessment of the long-term solder stability, and conduction capacity, specific tests have been designed, to determine a minimum needed resistance against high cyclic loads.

3 3) Tests referred to: Temperature Cycle Tests Power Cycle Tests 8 Substitution of concerned hazardous substances via materials and components not containing these is technically or scientifically either practicable or impracticable Because the currently available alternative Lead free soldering material, SnAgCu solder, and SnPb solder, have different physical characteristics (see table below), cracks and voids will more likely occur in the soldering phase. The risk of a detriment of the in-vehicle reliability is increased. Therefore the substitution is technically yet impracticable. Fig 7.1 Photo of chip The figure shows the Si chip soldered to the metal base. Table 7.1 Comparison: Hardness and elongation Young's modulus (E) Elongation SnPb SnAgCu GPa % Hardness HV Melting point Solder spread (240 ) deg. % Above data is representative for each material: SnPb: eutectic solder SnAgCu: Sn3.0Ag0.5Cu Data of Young s modulus, Elongation, Hardness and Melting point taken from Fujitsu online database. Crack expansion investigation The shape of a crack is usually sharp and straight. Greatest matter of concern is the progression of the crack under cyclic load. Following picture shows a soldering joint being cracked due to the cyclic thermal loads. Solder material is SnAgCu solder.

4 Fig 7.2 Crack in SnAgCu solder SnAgCu solder 10μm Crack 10μm The figure shows a straight crack, progressing from the outer side. The SnAgCu solders phase structure does not prevent the expansion of the crack. Fig 7.3 Crack in SnPb solder α - Pb β - Sn This figure, the structure of the solder shows the 2 phases of Pb and Sn. The phase structure shows more ductile properties then the one of the SnAgCu, especially considering creep fatigue. Void forming The process of void forming is caused by the vaporization of contained materials, such as of the fluxing agent, which is added to improve the wetting of the soldered surfaces. Fluxing agent contains many chemical substances, some of which are changing their status from liquid to gas in the soldering process. The gases are causing void inclusions, if they can not evaporate from the liquid solder. The higher the liquidity of the solder material during the process, the easier the gases can be released out of the solder. The liquidity of SnPb solder is better than those one of the lead free SnAgCu solder.

5 Fig. 7.4: Void forming Photo shows solder samples processed in a reflow oven under similar conditions. The SnAgCu solder is lead free. SnAgCu SnPb Void Temperature Cycle Test: Void comparison After the TCT, the void content on the crack surface of lead free and lead containing solder is documented. A soldered connection was exposed to the conditions of the TCT over 4000 cycles, after which following photos were taken by Scanning Acoustic Tomography. Fig. 7.5: Voids on crack surface Lead free solder: Void SnAgCu 0 cycles 4000 cycles Lead containing solder: Void Sn50Pb 0 cycles 4000 cycles

6 The pictures show that the occurrence of voids in SnAgCu solder and in SnPb solder is following different rules. The expansion of crack in SnPb is initiated from outside the chip, as it is expected and anticipated in simulation (ref. to: Temperature Cycle Test simulation). For the SnAgCu solder, the crack propagation is different from the expectations: Voids form everywhere and the total void content is higher. Research is focusing on the difference of crack expansion theories and the mechanisms of void increase with increasing cycles. 9 Elimination or substitution of concerned hazardous substances via design changes is technically or scientifically either practicable or impracticable 10 Negative environmental, health and/or consumer safety impacts caused by substitution are either likely or unlikely to outweigh environmental, health and/or consumer safety benefits thereof (If existing, please refer to relevant studies on negative or positive impacts caused by substitution). The described design of power modules containing die bonded Si chips is a new development. A design change could possibly reduce or make obsolete the need for using SnPb solder. However, the described design is now just about to show its functionality in the practise. Any a design change should be linked to the development of a second generation of the power modules. Therefore, the change of the design is at that moment impracticable. The described design of power modules containing Si chips (IBGT) that are die bonded are used as a major innovative component in hybrid electric vehicles (HEV) and in electric vehicles (EV). In those vehicles, a fast and energy-efficient control of voltage and current must be assured, with fast and abrupt changes of the direction (to / from the battery). These vehicles must function in similar environment and with similar robustness as any other vehicle that is on the market. HEV have the potential to realize a saving of fuel compared to similar vehicles with a combustion engine alone. (Ref. to: CARS 21 Mid-Term Review Conclusions and Report) What EV concerns, these are widely recognised as the most environment friendly and future relevant means of personal road transport, as any local emission of exhaust gases becomes obsolete. 11 Please provide sound data/evidence on why substitution / elimination is either practicable or impracticable (e.g. what research has been done, what was the outcome, is there a timeline for possible substitutes, why is the substance and its function in the application indispensable or not, is The assessment of alternatives for the SnPb solder is matter of research that has just started. Most important criterion for failure / non-failure is the tendency of a solder to withstand crack propagation under thermal stresses. Thermal stresses, with steep variations of the amplitude, result from the power cycles occurring during the normal in-duty use of the modules. Temperature Cycle Test: simulation First results obtained by numerical simulation are available. The simulations were carried out using a CAD model as shown in figure 10.1.

7 there available economic data on the possible substitutes, where relevant, etc.). The load is assumed to be thermal induced stresses following the conditions shown in figure Failure criterion is the (simulated) crack length failure condition is the amount of thermal cycles Fig 10.1 Model Fig 10.2 TCT Loading (simulation) The cyclic load simulates the condition of high stress fatigue with long holding times. Temp [ ] cycle Time [min] Amplitude of temperature: - 40 to +125 Holding time: 15 min Cycle time: 36 min Fig 10.3 TCT result

8 Length of Crack [um] 2500 SnPb SnAgCu Result Turning point Number of cycles Power Cycle Test The tests are performed with real components under realistic conditions. Therefore, the soldered chips are loaded with an electric current, similar to the maximal current they experience in duty. Failure criterion is the measured crack length Failure condition is the amount of electric (and resulting thermal) cycles. Fig 10.4 PCT Loading (real part test) The load, electric current, is applied by switching on and off Ic Tj Ca. 100A ON few sec Tj_max OFF sec T: ca. 50 Time Amplitude of current: 0 to 100A Holding time: few seconds Cycle time: about 20 seconds

9 Results of the Power Cycle Test are not yet available. Tests with similar conditions have resulted in the appearance of propagation, as shown in figure 7.2. Conclusion The solder must offer a good balance of hardness and elongation, to withstand cyclic thermal stresses. Not enough experience is yet available regarding the estimation of the life time of lead free soldered joints, especially under the condition of existing sharp and straight cracks. The development of a suitable new solder, and the development of process condition for the production and production facilities is ongoing. The evaluations are ongoing, but results are not yet promising enough to initiate a material change. 12 Please also indicate if feasible substitutes currently exist in an industrial and/or commercial scale for similar use. 13 Please indicate the possibilities and/or the status for the development of substitutes and indicate if these substitutes were available by 1 July 2003 (ELV) or by 1 July 2006 (RoHS) or at a later stage 14 Please indicate if any current restrictions apply to such substitutes. If yes, please quote the exact title of the appropriate legislation/regulation 15 Please indicate benefits / advantages and disadvantages of such substitutes. 16 Please state whether there are overlapping issues with other relevant legislation such as e.g. the Energy-using Products (EuP) - EuP In existing hybrid-electric vehicles (HEV), power modules are used that were produced using high melting temperature solder with a Lead content of at least 80%. The application is similar to the here described one. Please refer to exemption request for "High melting temperature solder" There were and are no substitutes available that are technically feasible given the degree of reliability requested. not known. See above According to Art 1 (3) the EuP directive shall not apply to means of transport for persons or goods. There is also no overlapping issues with the RoHS (see above) or the battery directive. However, there is a clear overlap with the REACH regulation. Therefore, substance restrictions should be excluded from the EU ELV directive as

10 Directive (2005/32/EC) that should be taken into account. 17 If a transition period between the publication of an amended exemption is needed or seems appropriate, please state how long this period should be for the specific application concerned. they are not relevant for recycling. Exemption for vehicles type and spare parts for these vehicles. Because no feasible alternatives are existing, a review of the exemption before 2015 is not proposed.