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Content archived on 2024-04-30

Development of adaptive solder technology for reliability and environment compatibility of electronic assemblies


The technical achievements are the following:

- A fundamental understanding of the action of SMA particles into solder paste matrixes: an extensive study of SMA particles has been conducted by CNRS-ICMCB and SIMR.

- A proven small SMA particles (" 1 µm in diameter) powders production process: it has not been possible to produce micronic SMA particles, because it has been found that decreasing the particles size was leading to Shape Memory properties disappearance. However the finest produced ever SMA powders have been obtained (0.3 to 8µm diameter distribution) using the Nanoval Gas Atomisation Technology.

- A proven SMA powders coating process: after several trials and many optimisation a satisfying Nickel/Gold coating has been developed. However it was found that it was not possible to obtain a complete cohesion between the SMA particles and the metallic coating, possibly due to the high level of oxidation of NiTi and the presence of several impurities came from the powders manufacturing processes.

- A proven coated SMA powders inclusion into solder pastes: after several trials it has been possible to include SMA powders into different solder alloy matrixes (eutectic SnPb and lead free SnAgCu).

- The availability of small quantities of a family of adaptive solder pastes: several paste formulations, using different kind of SMA particles, have been issued during the project. However we consider that only the last one (SnAgCu/SnPb + 5.6%wt 36-53µm Ni/Au coated GKSS NiTi powder) obtained can be considered as available, for the other pastes exhibited too low processability (due to agglomeration problems).

- The processability of developed adaptive solder pastes was verified and validated using standard screen printing, component assembly and re-flow techniques in PHILIPS CFT facilities,

- A number of prototype electric circuits produced with adaptive solder pastes: two different testboards have been designed using very different kind of components, in order to evaluate adaptive pastes performance for microelectronic applications, with respect to the different end users specifications.

- An improvement of the reliability of future electronic assemblies compare to the assemblies made with SnPb solder: despite all the effort put by the scientific partners and the end-users, it has not been possible to demonstrate that the incorporation of SMA particles was leading to a assembly reliability improvement. As a matter of fact, it appeared that, even if the theoretical fatigue performance of the developed adaptive paste was found slightly higher than corresponding solder alloy matrixes, its second level assembly reliability was found at the best similar than the ones from the previous alloys.
Today, the electronic industry faces two major challenges:- Increasing the reliability of electronic assemblies and, as a consequence, increasing functionality and reducing the cost;- Eliminating the undesirable environmental impacts associated with their production. The solder joint combines these two challenges. In fact the solder joints used in the construction of electronic circuits serve the three primary purposes of electrical interconnection, mechanical attachment and heat transfer of components to circuits boards. The major problem of electronic assemblies is caused by the differences in coefficients of thermal expansion between the materials joined by the solder joint. This limits the size of components that can be used reliably and hence the scale of integration. The fact that the great majority of solder pastes contains Lead (Pb) is an environmental threat. And the fact that extra-material has to be used to compensate for the limitations of the solder joints add extra cost to the electronic circuits. The purpose of the ASTRAL project is to overcome these challenges by developing a new family of Lead-free solder pastes made by incorporation of superelastic Shape Memory Alloys into Lead-free matrixes. The experiments made by some of the partners have proven that this approach is viable.

The novel high performance adaptive solder paste will have many benefits including:- Improving the solder joint mechanical characteristics;- Improve reliability of electronics- Increasing the size of components usable reliably;- Increase the scale of integration & speed;- Suppressing the Lead;- Environmental benefit- Suppressing the need of extra-materials;- reduction of cost.

The main result of this project will be a new family of high performance Lead-free solders. The consortium comprises 5 end-users (4 large companies and one medium size), which cover the major applications of electronics: consumer, industrial, automobile, telecommunication and aerospace. It includes also a well-known solder pastes manufacturer, a small but well established SMA producer and two complementary research organizations.

Specifications of the end products will be given by partners 1, 6, 7, 8 and 9 (end-users) who will assess the actual properties of the developed products. Simulations, definition and test will be provided by partners 2,4 (ROR) and 5 (SMA fabrication) in co-ordination with partner 3 (solder pastes). Partner 5 will produce the SMA powders, which will by included in solder pastes by partner 3. In the last phase of the project the ASTRAL technology will be demonstrated and the improvements assessed. The consortium brings together 9organizations from 5 EU countries. It covers the major electronic applications and presents a multidisciplinary approach, which will give advantages to the majority of companies in EU active in the use or manufacturing of electronic products. The total direct and indirect economical benefits will amount to at least 200Mecu par year to the EU economy after full implementation. It will help produce better, lighter, more reliable electronic products and as a consequence will help maintaining a high quality, high level of employment in a sector which employs over 2 Million people in the EU. BE97-5109

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