DE3909677A1 - Spray additive for thermal spraying of solderable layers of electrical components - Google Patents

Abstract

The spray additive for thermal spraying of the Schoop layers of electrical components, especially capacitors, are admixed with a small proportion of phosphorus, in order to prevent, in advance, subsequent oxide formation on the contact layers.

Description

The present invention relates to a spray additive for ther mixing syringes of solderable layers of electrical components, especially the front contact layers of electrical condensate ren, consisting of at least tin and / or lead metal alloy.

The spray additive of the invention is particularly preferred Capacitors used, but also with all other electri cal components, such as connectors, if it depends on the generation of solderable spray layers.

Capacitors in the sense of the present invention are stacked or layer capacitors, but also flat-pressed winding cones capacitors as are known per se. Such condensate gates consist of many layers of a metallized art dielectric material, for example polyphenylene sulfide or Polyethylene terephthalate. On the end faces of the capacitor bodies are applied by thermal spraying, metal pads wear, for example by the known Schoop-Ver drive that serve the alternating in the end faces reaching metallizations of the dielectric layers elek to connect with each other.

Details of the technique of thermal spraying can be found in the Take DIN standard 32 530.

In the context of surface mounting technology (SMD technology) increasingly non-coated film capacitors are used, the are intended for direct soldering on printed circuit boards. Here However, problems arise because the condens used so far thermally sprayed, essentially made of Tin-lead alloys existing metal layers oxide layers train that reduce the solderability.  

It is known for adequate wetting of an object with solder in addition to the material, especially the purity of the surface decisive. Therefore, impurities have an effect on for example, oxides are very disadvantageous. The oxide layers on the unprotected Schoop areas are increasingly caused by tem influence of temperature in connection with tempering processes or pre heat stretches during the manufacturing process of the capacitors and later during the installation in the circuit board. In principle it is possible, but disadvantageous in practice, the un desired oxide formation through subsequent mechanical and / or counteract chemical measures.

Unlike in surface mounting technology, the oxide layers in the conventional assembly technology of construction elements did not appear to be particularly problematic at first. Here, too, soldering of the looped capacitors is necessary necessary on the circuit board, but they are sprayed on layers are not in direct contact with the circuit board, but via additional connection elements, for example wires te or caps. In a common process, for example white wires by spot welding onto the thermal spray attached metal supports. The welding energy is like this high chosen that the oxide layer is destroyed. This procedure However, ren is not completely satisfactory, since such a high one Welding energy endangers the capacitor.

The object of the invention is therefore thermal to create sprayed layers on electrical components fen, where problems with oxide layers, especially in Hin view of contactability, do not occur.

This object is achieved in that the Spray additive mentioned at the beginning also contains phosphorus.

The task is surprisingly the simplest Way solvable.  

The invention is based on the knowledge that there are problems with and subsequent measures to remove the oxide layer easiest to avoid by forming an oxide of is prevented in advance. Although the is anti-oxidant Effect of phosphorus known in principle. So far this is but not in thermal spray materials exploited.

The starting material in thermal spraying, i.e. H. the Spray additive, for example as a solid wire or as Powder is available. How successfully carried out experiments shows, it is sufficient to use the usual spray wires on tin Lead base, for example a white metal flame spray wire, add a few thousandths by weight of phosphorus at most gene to the undesirable oxide formation from this material reliably prevent manufactured metal pads. Ent The decisive factor is that the proportion of phosphorus in thermal spraying not evaporated, but also to a sufficient extent sprayed metal pad is present.

It is particularly advantageous if the ratio of Weight percent of tin and lead of about 3: 2 in the flame spray The phosphorus content used for the flame spray wire metal alloy between 0.001 and 0.004 percent by weight is.

Claims (3)

1. Spray additive for thermal spraying of solderable layers of electrical components, in particular end contact layers of electrical capacitors, consisting of a metal alloy containing at least tin and / or lead, characterized in that the spray additive additionally contains phosphorus. 2. spray additive according to claim 1, characterized, that the phosphorus content of the spray additive is between 0.0005 and 0.007 percent by weight, preferably between 0.001 and 0.004 Weight percent is. 3. spray additive according to claim 1, characterized, that with a ratio of the weight percent of tin and lead of about 3: 2 the phosphorus content of the spray additive between 0.002 and 0.003 percent by weight.