WO2011023641A2

WO2011023641A2 - Radiation-emitting device, and method for the production of a radiation-emitting device

Info

Publication number: WO2011023641A2
Application number: PCT/EP2010/062189
Authority: WO
Inventors: Jörg Erich SORG
Original assignee: Osram Opto Semiconductors Gmbh
Priority date: 2009-08-28
Filing date: 2010-08-20
Publication date: 2011-03-03
Also published as: TW201126772A; WO2011023641A3; DE102009039245A1

Abstract

Radiation-emitting device comprising a lead frame (1), a radiation source (3) that is arranged on the lead frame, an electrically conducting contact (2) that connects the lead frame in an electrically conducting manner to the radiation source, and a molding material (4) that is arranged on the surface of the radiation source. The molding material comprises an additive (5) that can absorb H⁺ ions or neutralize H⁺ ions by discharging OH^- ions.

Description

description

Radiation-emitting device and method for

Production of a radiation-emitting device

This patent application claims the priority of German Patent Application 10 2009 039 245.9, the disclosure of which is hereby incorporated by reference.

A radiation-emitting device according to claim 1 is specified.

A common problem of radiation emitting devices is that it can fail or

Damage due to corrosion can occur. Here, individual components, which are part of the

Radiation-emitting device are attacked by corrosion and restricted in their functioning. The components can even be damaged by the corrosion

completely lose their functionality, which can result in failure of the entire radiation-emitting device.

Corrosion is generally understood to mean the reaction of a material with its environment, which is a measurable one

Change of the material causes and to a

Impairment of the function of a component or a

Systems can lead. In chemistry, corrosion refers to the chemical reaction or electrochemical reaction of a material with materials from its environment, with a measurable change in the material. When a nobler metal comes into contact with a less noble metal, a local element is created at the contact point Corrosion of the less noble metal can lead. This can lead to the oxidation of the less noble metal, which is the

Formation of metal ions result, which can go into solution or migrate into an adjacent substance. Thus, for example, atmospheric moisture or reactive gases from the air / atmosphere surrounding the device penetrate into the interior of the device and lead here to the corrosion of, for example, metallic components of the device.

To counteract this problem have been so far

pursued different approaches. One of them is based on sealing the device at its radiation exit side, so that hardly any moisture in the

Radiation-emitting device can penetrate. The

Problem here is that it is very expensive, one

to achieve sufficient tightness. Some of the materials which could achieve sufficient tightness do not satisfy other necessary requirements, such as, for example, sufficient transparency for the radiation emitted by the radiation-emitting device or sufficient stability to the emitted radiation.

Another approach attempts to use materials that do not differ in electrochemical potential, thereby avoiding the formation of a local element. The electrochemical potential is the chemical potential of an ion or other charge carriers, such as electrons, in an electrical potential. Potential difference is the ability of a system

described to do work. For example, chemical reactions involving charge carriers occur until the electrochemical potentials of the involved system components are balanced.

Potential differences occur, for example, on the

Contact surfaces of two metallic materials, which have a different electrochemical potential. This can lead to the production of the device for all metallic components very expensive metals

must be used, although this would not be necessary in their function. This leads to a significant increase in production costs.

In another approach, the attempt is made

To mask corrosion-sensitive components of the device by means of an inert material. This can

For example, with barrier layers between the

metallic layers are introduced with potential difference happen. However, this requires additional

Process steps and an additional use of materials, which in turn increases the cost of manufacturing.

The object of reducing the corrosion is achieved by a radiation-emitting device according to claim 1. Further embodiments of the radiation-emitting device are the subject of further dependent

Claims. Furthermore, a method for

Production of a radiation-emitting device

claimed.

An embodiment of the radiation-emitting device comprises

a ladder frame,

- A radiation source, which on the lead frame

is arranged - An electrically conductive contact, which the

Conductor frame electrically conductively connects to the radiation source,

a potting material which is on the surface of the

Radiation source is arranged,

the potting material comprising an additive capable of absorbing H ⁺ ions or neutralizing them by release of OH ^~ ions.

The inventors have recognized that H ⁺ ions, which penetrate from the outside into the component or are formed by a reaction in the component, contribute to the corrosion. In a partial reaction, electrons are taken up by the H ⁺ ions from the nobler metal of the local element, whereby H ₂ forms. These electrons are derived from the less noble metal of the

Local element given to the nobler metal due to the differences in the electrochemical potentials. The oxidation of the less noble metal ions can lead to corrosion of the component, which is made of the less noble metal.

Furthermore, the inventors have recognized that reducing a partial reaction leads to the reduction of all reactions involved in this process and thus also to corrosion.

The additive can be distributed in the potting material

present and act as H ⁺ ion scavenger or as OH ^~ - ion donor. For example, the additive can deliberately prevent a partial reaction which contributes to corrosion or to chemical reactions which can lead to corrosion.

The additive may, for example, in powder form the

Casting material can be added. Such a powder could then additionally assume the function of a diffuser and contribute to the homogenization of the radiation characteristic.

The additive should also meet one or more of the following criteria:

Temperature stability against the heat emitted by the radiation source, radiation stability against the radiation emitted by the radiation source (e.g., UV radiation), and chemical compatibility with the potting material.

In a further embodiment of the radiation-emitting device exists between the lead frame and the

Contacting in the contact area an electrochemical

Potential difference.

Such an electrochemical potential difference can

For example, occur in that two different metals are used for the lead frame and the contact, resulting in the formation of a local element result. The system of ladder frame and contacting is now

anxious to balance the potential difference, what

can be done for example by electron transport. Here, the electrons flow from the less noble metal to the nobler metal. For example, in a system of copper and gold, electrons are transferred from copper to gold.

The corrosion occurring in a device has a velocity which is related to the magnitude of the current flowing through these devices. The current in turn is due to the reaction rate of

The slowest reaction determines which is involved in charge transport. In another embodiment, the lead frame is in direct contact with the potting material.

Thus, for example, it can be used to deliver ions of the

Metal, from which the lead frame is made, come directly into the potting material. As a result of the release of the positively charged metal ions, it is thus possible for charge equalization to occur compared with the electrons transferred to other components.

In a further embodiment, the potting material comprises a silicone. For example, silicone has better stability against the emitted radiation compared to epoxide. But it is also the use of hybrid material, ie materials which consist of silicone and epoxy materials conceivable.

In a further embodiment of the radiation-emitting device is the addition of the pH in the

Casting material set. In turn, partial reactions of the corrosion should be regulated or prevented via the pH value.

In a further embodiment, the pH is in the

Potting material above 7. This means that the pH is in the alkaline range. This allows H ⁺ ions, which are present in the potting material, because they are either from a

Component of the device have been delivered or were taken from the environment or by a reaction in the

Casting material are formed, neutralized. By this neutralization, for example, the partial reaction of corrosion can be prevented, in which the H ⁺ ions absorb electrons from the nobler metal. Preferably, the pH of the potting material is in the range of 8 to 13. More preferably, the pH of the potting material is in the range of 8 to 11.

In this pH range, the potting material is well able to neutralize free H ⁺ ions. The potting material itself is not so strong that it is alkaline

Damage to the components of the radiation-emitting

Device is coming.

In one embodiment, the additive comprises a

Metal hydroxide.

A metal hydroxide has the advantage of being a good one

Radiation stability has. Furthermore are

Metal hydroxides apart from the desired property of their alkalinity chemically inert, so that no unwanted chemical reactions between the additive and the

Casting material occur. The metal hydroxide may, for example, be Al (OH) 3. The metal hydroxides can be added to the potting material in powder form, for example.

In a further embodiment, the additive comprises a zeolite.

The primary building blocks of zeolites are AlC ^ tetrahedra or SiO ₄ tetrahedra, which share common oxygen ions

be connected together to the secondary building units. By linking the secondary building units, a three-dimensional crystalline framework is created which, depending on the zeolite, differs from regular pore and cavity systems. Licher size, arrangement and architecture is pervaded. For each A10 ₄ tetrahedron incorporated into the aluminosilicate framework, the resulting zeolite framework contains a negative charge which must be compensated for by a positive counter charge. This can be done, for example, by storing cations in the pores and cavities of the zeolite. Thus, for example, Na ⁺ , Ca ²⁺ or K ⁺ ions in the

Cavities of the zeolite are present. These can then be replaced by an ion exchange by other ions, such as an H ⁺ ion, and so in one embodiment of the invention as H ⁺ -aufnehmender additive in

Casting material can be used. Synthetic zeolites, for example, from strongly alkaline, aqueous

Solutions made of silicon and aluminum compounds. Examples of zeolites are the following compounds:

Na ₂ Ca [Al ₂ Si ₄ Oi ₂ J ₂ "faujasite", Ca [Al ₂ Si ₄ Oi ₂ ] "chabazite",

Na ₂ [Al ₂ SiI ₀ O ₂₄ ] "mordenite" or Na ₂ [Al ₂ Si ₃ Oi ₀ ] "natrolite". Zeolites also have a high radiation stability and are also chemically inert.

In a further embodiment, the additive comprises a metal hydride.

The metal hydrides are lattices which are formed of metals and which have a large internal

Surface has. Hydrogen can be in the

Interstitial sites are stored, for example via physisorption. The hydrogen is not installed on lattice sites. Such metal mesh will be

For example, TiFe, Mg ₂ Ni, ZrMn ₂ or LaNi ₅ formed. These systems are also stable to radiation and the metal meshes are chemically inert. In a further embodiment, the additive comprises an ion exchanger.

The ion exchanger may, for example, be a zeolite as described above. But there are also other ion exchangers, which are not zeolites, conceivable. For example, resin ion exchangers with active groups can be used. Depending on the type of ion exchanger, a distinction is made between cation exchangers and anion exchangers. In the case of a cation exchanger as H ⁺ -aufnehmenden

Additive, the active group is an anionic group, such as a sulfonic acid group or a

Carboxyl group. The counterion to this anionic group, which may be, for example, an Na ⁺ ion, may be in

Ion exchange process are replaced by an H ⁺ ion.

In a further embodiment, the additive is present in a proportion of 0.05 to 2% by weight in the casting material.

In these quantities, however, the additive reduces the undesired corrosion reactions but impedes them

on the other hand, not the emitted radiation in one

unwanted dimensions. A suitable amount of additives also depends on the appropriate choice of

Additive from. There is also the possibility in the

Potting material to combine different additives.

In a further embodiment, the leadframe comprises a metal Me.

Here, the entire lead frame may be made of the metal Me, or even only the electrically conductive

Structures that are applied to the leadframe. In another embodiment, Me is Cu.

Cu is a metal that lends itself very well to lead frames or the electrically conductive structures on the lead frame. Cu has a good stability and a high degree of electrical conductivity. Furthermore, Cu

relatively inexpensive compared to other metals such as Ag or Au.

In a further embodiment of the radiation-emitting device, the radiation source is an LED.

The LED comprises a semiconductor which forms a diode. LEDs are often called III / V semiconductors, i. they are composed of elements of the 3rd and 5th group of the periodic table. Furthermore, the LED includes an anode, which itself

for example, located on the top of the LED, and a cathode, which may be arranged on the bottom corresponding. The anode can be electrically conductively connected via a bond wire to the lead frame on which the LED can be arranged. When a voltage is applied in the forward direction, electrons migrate to the recombination layer at the p-n junction. On the n-doped side, the electrons populate the conduction band in order to change to the more favorable p-doped valence band after crossing the interface. There, the electrodes then recombine with the ones here

existing holes.

However, embodiments are also conceivable in which the radiation source is an OLED. Of the

Layer stack which can form an OLED comprises an anode as well as a cathode. These are going through Applying voltage given holes or electrodes, which migrate toward the other electrode. The

For example, charge carriers first migrate through holes or electron-transporting layers before they meet in the emitting layer. In this, the electrons recombine with the holes, causing

Excitons are formed. The excitons can then

Phosphors which are in the emitting layer to excite radiation.

In a further embodiment, there is an electrochemical potential difference between the radiation source and the contacting in the contact region.

If a different material is used for the contacting, which can take place, for example, via a bond wire than for the region of the component at which the contacting takes place, for example the upper electrode, this results in the formation of a local element. As already explained above for the potential difference, it is therefore also possible in this contact region for the transfer of electrons from the less noble metal to the more noble metal.

In a further embodiment of the radiation-emitting device, this comprises a cathode and an anode.

In a further embodiment, the anode at the same current to a greater current density than the cathode.

Another criterion for the local corrosion rate is the current density. High current densities lead to high corrosion rates. The current density is a function of the current and the surface involved. For example, indicate the anode and the cathode or the metal surfaces where cathodic or anodic

Reactions take place on a different size, so this results in a different current density. For example, in a radiation-emitting device in which the surfaces of the anode and cathode have a very large difference in size, easier

Form short-circuit elements. For example, the

Surface of a reaction only a small one

Defective, which has only a very small size. In contrast, for example, the contact, which runs through the potting material, with almost its entire surface in contact with the potting material. This surface difference, which can result in very high current densities in very small areas, may be responsible for locally very high levels

Corrosion rates occur.

In a further embodiment, the absorption of the H ⁺ ions reduces the corrosion in the component. The uptake of the H ⁺ ions can be carried out by the additive.

In a further embodiment, the absorption of the H ⁺ ions controls the pH in the potting material. By taking up the H ⁺ ions, which can be done by the additive, the pH in the potting material to a

desired value can be set. This refers both to the pH present in the potting material when it is applied in or on the device, that is to say in a state in which no chemical reactions still take place. It also refers to the pH value that is sought when chemical reactions occur throughout Lifetime of the radiation-emitting device in the

Potting material take place.

In another embodiment, lowering the H ⁺ ion concentration reduces the following reaction: 2H ⁺ + 2e ^- → H ₂ (Reaction 1).

In a further embodiment, the reduction of Reaction 1 reduces the following reaction: Me → Me ^{m +} + me ^~ (Reaction 2).

Due to the trapping of the H ⁺ ions by the additive, the electrons in reaction 1 lack the reaction partners, so that this reaction can only proceed with difficulty. Because no electrons are "consumed" in reaction 1, the reaction 2, in which new electrons are made available, is reduced because there are no consumers available for them. By reducing reaction 2, the transition from Me to Me ^{m +} , that is, the solution of metal ions from which the lead frame is made,

reduced. Thus, damage to the lead frame is reduced.

In addition to the radiation-emitting device is also a method for producing a radiation-emitting

Claimed device.

In a variant of this method, this includes the

Process steps:

A) providing a lead frame (1),

B) applying a radiation source (3) to the ladder frame (D, C) producing an electrically conductive connection between the leadframe (1) and the radiation source (3) by means of an electrically conductive contact (2),

D) encapsulating the radiation source (3) with a

Potting material (4), wherein the potting material (4) comprises an additive (5) which is able to take up H ⁺ ions, or these by the release of OH ^~ ions to

neutralize.

In the process step D), an additive may be used, as described for example in the embodiments previously in connection with the device.

The features and advantages embodied in connection with the device also apply correspondingly to the components / materials used in the method.

In the following, variants of the invention based on

Figures and embodiments will be explained in more detail.

FIG. 1 shows a schematic cross section through an embodiment according to the invention

Radiation-emitting device.

FIGS. 2a and 2b each show a further one

inventive embodiment of a

Radiation-emitting device in

schematic cross section, which comprises a housing.

Figures 3a and 3b each show a section of a

Radiation-emitting device in schematic cross section in the unwanted

Corrosive reactions take place.

FIG. 1 shows a schematic cross section of a

Embodiment comprising a lead frame 1. On the lead frame 1, a radiation source 3 is arranged, which is electrically conductively connected with its underside with a first portion of the lead frame 1. The top side of the radiation source 3 is connected via a contact 2

electrically conductive with a second portion of the

Lead frame 1 connected, which compared to the first

Part area is electrically isolated. The contact 2 and the lead frame 1 in this case form a contact region 6. Both the radiation source 3 and the contact 2 are surrounded by a potting material 4, whereby these two components are encapsulated. The potting material 4 in this case comprises the additive 5.

The lead frame 1 may comprise, for example, Cu, the

Contact 2, for example Au. As a radiation source 3, for example, an LED can be used. The

Potting material 4 may include, for example, a silicone.

In the case where the leadframe 1 and the contact 2 are made of different materials or of materials which have a different electrochemical potential, there is a potential difference between the contact 2 and the leadframe 1 in the contact region 6.

By the penetration of an electrolyte, for example

Humidity, it can contribute to the formation of a

Shorting element come. FIG. 2a shows a schematic cross-section of another embodiment of the radiation-emitting device.

This includes, as shown in Figure 1

Embodiment, also a lead frame 1, a

Radiation source 3 and a contact 2. The

Contact 2 connects the upper side of the radiation source 3 in an electrically conductive manner to a partial region of the leadframe 1. In this case, the contact 2 and the leadframe 1 form a contact region 6 in the region in which they are connected to one another. The embodiment shown in Figure 2a additionally comprises a housing 7. The cavity of the housing 7, in which the radiation source 3 is arranged, is filled with a potting material 4. This includes the additive 5.

The embodiment illustrated in FIG. 2b as a schematic cross section largely corresponds to that which is shown in FIG. 2a. However, the embodiment shown in Figure 2b additionally comprises a barrier layer 8. The barrier layer 8 is arranged between the radiation source 3 and the lead frame 1, whereby the latter is masked. The underside of the radiation source 3 is electrically conductively connected via the barrier layer 8 to the lead frame 1. The contact 2 extends from the top of the radiation source 3 now to the surface of the barrier layer 8. The contact region 6 is thus in this embodiment

between the contact 2 and the barrier layer. 8

educated. But even between the barrier layer 8 and the lead frame 1 is a potential difference. The

Barrier layer 8 can largely prevent, for example, a dissolution of the leadframe 1, that is to say a release of metal ions from the leadframe into the potting material 4. However, such a barrier may also be used, for example Have pores or voids through which metal ions can migrate.

FIG. 3 a shows a section of an embodiment of the radiation-emitting device as a schematic cross-section. The section shows a lead frame 1, on which a barrier layer 8 is applied. On the barrier layer 8, the contact 2 is applied, which leads in its extension, not shown, to the radiation source 3. The contact 2 is electrically conductively connected to a portion of the Leiterrahmes 1 via the barrier layer 8. The potting material 4 is applied over the barrier layer 8 and is in the area in which the barrier layer 8

is interrupted, even in direct contact with the

Lead frame 1. The potting material 4 comprises a

Additive 5. The barrier layer 8 may be interrupted for example by defects 9 or pores in the material. The flaws, for example, a consequence of a

Reaction of the material of the barrier layer 8 with a

Pollutant from the environment or an impurity: Ag ⁺ + S ^~ -> AgS. The potting material 4 comprises in this embodiment a silicone. In the embodiment shown here, the lead frame 1 made of Cu, the

Barrier layer 8 of Ag and the contacting 2 of Au. Thus, the lead frame 1, the barrier layer 8 and the

Contact 2 or the metals from which they are made, an electrochemical chain Cu / Ag / Au. Here Cu is the most precious metal and Au is the noblest metal. In the

Areas in which the components of these metals are in contact with each other, so is one

Potential difference before. This potential difference is the driving force for the migration of electrons from the lead frame 1 through the barrier layer 8 for contacting 2. Figure 3b now shows possible reactions which in the

Section, as shown in Figure 3a, can run. Due to the high permeability of silicone, H ₂ O and SO ₂ from the environment can penetrate into the potting material and react to form 2 H ⁺ and SO ₃ ^{2 ~} , sulphurous acid.

Alternatively, the sulfur may also be introduced into the potting material 4 from outside by, for example, H ₂ S or other sulfur-containing compounds. The H ⁺ ions can now accept electrons at the contact 2, which is made of the noblest of the three metals, whereby they are converted into H ₂ . In the flaw 9 of the

Barrier layer 8 is the potting material 4 in direct

Contact with the leadframe 1. This will allow the Cu ions of the leadframe to enter directly into the leadframe

Potting material 4 can be discharged, whereby electrons are discharged. In the transition from Cu to Cu ²⁺ two electrons are released, which are forwarded via the barrier layer 8 for contacting 2 due to the potential difference described above. The Cu ²⁺ ions in the potting material 4 can further react with the Sθ ₃ ^{2 ~} ions to CUSO ₃ , which can be deposited on the barrier layer 8.

By the additive 5 in the potting material 4, the H ⁺ ions are now intercepted (schematically indicated by the arrow), so that the reaction of H ⁺ ions to hydrogen at the

Contacting 2 can no longer take place. In the case where the additive 5 is Al (OH) 3, the trapping of the H + ions can be effected by the following reaction: Al (OH) ₃ + 3H ⁺ -> Al ³⁺ + 3H ₂ O. The fact that the reaction in which the electrons are consumed is now suppressed or reduced also causes the reaction in which the

Electrons are formed, prevented or reduced. This means that at the defect 9 thus less or no Cu ions go into solution more. The life of the lead frame 1 is thus improved

Increased corrosion stability. Due to the fact that no or less Cu ions can go into solution, the formation of the CuSθ3 precipitate is simultaneously reduced or prevented. As a result, the lead frame 1 can be effectively protected against corrosion, although moisture from outside in the

Potting material 4 can penetrate, and this is in some areas in direct contact with the lead frame 1.

The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Features, which in particular includes any combination of features in the claims, even if these features or this combination of features is not even explicitly stated in the claims or exemplary embodiments.

Claims

claims

A radiation emitting device comprising

a ladder frame (1),

a radiation source (3) which is arranged on the lead frame (1),

- An electrically conductive contact (2), which the lead frame (1) electrically conductive with the radiation source

(3) connects,

a potting material (4) which is arranged on the surface of the radiation source (3),

wherein the potting material (4) comprises an additive (5) capable of absorbing H ⁺ ions or neutralizing them by release of OH ^~ ions.

2. Radiation-emitting device according to claim 1, wherein between the lead frame (1) and the contact (2) in the contact region (6) has an electrochemical

Potential difference exists.

3. Radiation-emitting device according to one of

previous claims,

wherein the lead frame (1) is in direct contact with the

Potting material (4) stands.

4. Radiation-emitting device according to one of

previous claims,

wherein the potting material (4) comprises a silicone.

5. Radiation-emitting device according to one of

previous claims,

wherein via the additive (5) the pH in the potting material

(4) is set.

6. Radiation-emitting device according to one of the preceding claims,

wherein the pH in the potting material (4) is above 7.

7. Radiation-emitting device according to one of the preceding claims,

wherein the additive (5) comprises a metal hydroxide.

8. Radiation-emitting device according to one of the preceding claims,

wherein the additive (5) comprises a zeolite.

9. Radiation-emitting device according to one of the preceding claims,

wherein the additive (5) comprises a metal hydride.

10. Radiation-emitting device according to one of the preceding claims,

wherein the additive (5) comprises an ion exchanger.

11. Radiation-emitting device according to one of the preceding claims,

wherein the additive (5) is present in a proportion of 0.05 to 2% by weight in the potting material (4).

12. Radiation-emitting device according to one of the preceding claims,

wherein the lead frame (1) comprises a metal Me.

13. A radiation emitting device according to claim 12, wherein Me is Cu.

14. Radiation-emitting device according to one of the preceding claims,

wherein the radiation source (3) is an LED.

15. A method for producing a radiation-emitting device, comprising the method steps:

A) providing a lead frame (1),

B) applying a radiation source (3) on the ladder frame

(D,

C) producing an electrically conductive connection between the leadframe (1) and the radiation source (3) by means of an electrically conductive contact (2),

D) encapsulating the radiation source (3) with a

Potting material (4), wherein the potting material (4) comprises an additive (5) which is capable of absorbing H ⁺ ions, or to neutralize them by release of OH ^~ ions.