JP2604593B2 - Method of forming solder coating on metal surface - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a coating of a solder alloy on a surface of a base metal. Generally, when an electronic circuit or the like is formed, a coating of a solder alloy is formed on an exposed base metal surface of a substrate on which a circuit pattern is drawn, and a desired circuit component is placed on the solder coating and heated. Melting the solder coating and joining the base metal and the circuit component by the solder are performed.

The present invention particularly relates to a novel method for forming a coating of a solder alloy on the surface of a base metal of such a circuit board.

2. Description of the Related Art Conventionally, in order to form a coating of a solder alloy on the surface of a base metal of a circuit board as described above, paste solder is usually used.

The paste-like solder is obtained by dispersing a powder of a solder alloy and a flux in a high-boiling solvent such as mineral spirit for adjusting viscosity to form a paste having a certain viscosity. In order to form a coating of metal solder on the substrate surface of the substrate using the paste solder, the paste solder is applied to the electronic component mounting board in a predetermined shape by screen printing or a dispenser. Is heated to melt the powder of the solder alloy, and the molten solder alloy is adhered to the base metal surface of the substrate with the help of flux to form a coating.

When the paste solder is heated, the powder particles of the solder alloy are melted, and the oxide on the surface of the molten solder particles is reduced by the flux to become pure solder molten particles,
The substrate metal surface is also reduced to form a clean surface. Thus, a coating of the metal solder is formed on the surface of the base by the cohesive force of the molten solder particles and the wettability of the solder particles to the base metal.

Problems to be Solved by the Invention However, in the paste solder, the solder alloy in the paste is free metal particles separated from the flux and the solvent, and the particles are said to be fine. However, it does not constitute a uniform composition with the flux and the solvent. Attempts have been made to reduce the size of the solder alloy particles, but currently the limit is around 10μ.

On the other hand, in recent years, the degree of integration of electronic circuits has increased, and circuit patterns on substrates have also been formed with fine lines at high density. In recent years, circuit patterns have been formed by drawing lines of about one hundred to several hundred μ at approximately the same intervals, and even when supplying paste-like solder on the substrate, the circuit pattern It is necessary to supply with extremely high precision in accordance with the increase in the density of. Therefore, when supplying paste-like solder by screen printing, a screen with a finer mesh must be used, and when a dispenser is used, it is necessary to use a discharge hole with a smaller diameter. ing.

However, as described above, since the solder paste contains solid powder particles of the solder alloy, the size of the solder alloy particles is substantially ignored when supplying the solder alloy onto the substrate by screen printing or a dispenser. I can no longer do it.

In the case of supplying by screen printing, powder particles of the solder alloy cause clogging of the screen, and it is difficult to print and supply the solder alloy uniformly in a predetermined shape. Also, due to the friction between the solder powder and the screen,
The mask may be scratched or damaged, shortening the life of the screen.

Also, when using a dispenser, the solder powder may be clogged in the narrow discharge holes, the clogged solder powder may pass through the subsequent paste, and discharge only the flux or the solvent, evenly including the solder alloy powder It is extremely difficult to discharge as a paste.

Further, as described above, bonding between the adhered metals is performed by the cohesive force between the particles of the molten solder and the wettability to the adhered metal, but the surface tension of each molten solder particle is large, and It is difficult for the solder particles to contribute to the bonding, and the solder particles that do not contribute to the bonding remain on the substrate, which may cause a short circuit between the circuits.

In particular, as described above, in electronic circuits with a high degree of integration, the spacing between the lines that make up the circuit is almost equal to the diameter of the solder particles, and shorts can easily occur even with a single solder particle. , Which can quickly lead to ground defects. In order to avoid such a situation, after the joining is completed, the electronic circuit is washed with an organic solvent to remove the remaining solder particles, but it is still difficult to completely remove the solder particles.

By making the diameter of the powder particles of the solder alloy smaller, these problems are somewhat improved, but it becomes expensive, and the particles of the molten solder become stable and hardly agglomerate. Not good.

Further, the portions other than the portion on which the metal film is formed on the substrate are masked with a resist agent, and a solder film is formed only on a predetermined portion, and at the same time, the solder is prevented from adhering to unnecessary portions, and the circuit is short-circuited. However, in this case as well, since the size of the portion where the solder film is to be formed is comparable to the size of each solder particle, the solder particles are surely applied to the predetermined portion. It is extremely difficult to supply and form a sufficiently thick solder metal coating.

Further, although a metal film is formed by immersing the masked substrate in a molten solder bath, it is also difficult to reliably form the film according to a fine pattern.

The present invention has been made in view of such circumstances, and tin and lead constituting a solder alloy are chemically bonded to an organic carboxylic acid, and a solution having a uniform composition is obtained by dissolving this in an organic solvent. None, by depositing solder metal on the surface of the base metal by immersing the base metal in the solution, and easily forming a metal coating on the surface of the base metal according to a precise pattern without considering the size of the solder particles. And to prevent a short circuit of an electronic circuit due to residual solder particles after the formation of the coating.

Means for Solving the Problems Accordingly, the present invention provides a method comprising dissolving a tin / lead mixed salt of an organic carboxylic acid or a mixture of a tin salt and a lead salt of an organic carboxylic acid in a high-boiling solvent under heating. , A metal having a greater ionization tendency than tin and lead is immersed, and a solder alloy is deposited on the surface of the metal.

The solute of the solution used in the present invention is obtained by converting a carboxyl group in an organic carboxylic acid as an organic component into a salt of tin and lead.

Various organic carboxylic acids can be used. For example, rosin or a derivative thereof, stearic acid,
Aliphatic carboxylic acids such as oleic acid, neodecanoic acid, sebacic acid, and fumaric acid, aromatic carboxylic acids such as benzoic acid, phthalic acid, isophthalic acid, trimellitic acid, and pyromellitic acid, and naphthenic acid can be used. . In addition to monobasic acids, dibasic or tribasic or higher polybasic acids can also be used. However, the organic carboxylic acid and the salt of tin and lead must be soluble in an organic solvent.

As these organic carboxylic acids, rosin or a derivative thereof is particularly suitable. As the rosin, in addition to gum rosin, tall oil rosin, wood rosin and the like, pure substances such as abietic acid and pimaric acid which are the main components of these rosins can be used.

In addition, as such rosin derivatives, asymmetric rosin, hydrogenated rosin, maleated rosin, fumarated rosin, and the like can also be used. In particular, maleated rosin or fumarated rosin is to be converted into a tribasic derivative by introducing carboxylic acid by maleating or fumarating rosin, and converting the three carboxylic acids of the rosin derivative into salts of tin and lead. Is preferable because the metal content can be increased.

For the introduction of tin and lead into the organic carboxylic acid, tin and lead salts can be obtained by adding a tin and lead salt to these organic carboxylic acid alkali salts and performing a metathesis reaction. Stannous chloride is suitable as the tin salt to be added to the alkali salt of the organic carboxylic acid, and lead acetate is suitable as the lead salt.

Further, the organic carboxylic acid may be heated and melted to react tin oxide and lead oxide, thereby obtaining a salt of tin and lead of the organic carboxylic acid.

In this case, a tin-lead mixed salt in which tin and lead are mixed and introduced into an organic carboxylic acid may be used, or a tin salt and a lead salt of an organic carboxylic acid are separately synthesized, and these are mixed with a predetermined amount. It may be mixed at a ratio.

However, in the latter case, the thickness of the obtained solder film tends to be relatively thick and the bonding strength tends to be large, and it is possible to freely prepare those having different tin and lead contents depending on the application. It is preferred because it has advantages.

The content of tin and lead contained in the tin and lead salts of the organic carboxylic acid varies depending on the type of the organic carboxylic acid,
About 2 to 70% by weight is appropriate, and more preferably 10 to 70% by weight.
It is desirable to be about 60% by weight.

The ratio of tin to lead in the tin and lead salts of organic carboxylic acids is
It is appropriate that the eutectic ratio of the solder alloy, tin / lead, is about 60/40, but it can generally be changed as appropriate within the range where the solder can be used.

In the present invention, as the organic solvent for dissolving the tin and lead salts of the organic carboxylic acid, those having a high boiling point are desirable, and for example, squalene, high-boiling mineral oil and the like are suitable.

As the ratio of the components in the solution, the concentration of the metal component in the organic carboxylic acid metal salt in the solution is at least
Desirably, it is 0.1% or more. Metal content
If it is less than 0.1%, the amount of the metal component is small, and a solder film having a sufficient thickness cannot be formed.

When the content of the metal component in the solution is set, a metal salt of an organic carboxylic acid having a relatively high metal content may be relatively dilutely dissolved in an organic solvent. A relatively low amount of a metal salt of an organic carboxylic acid may be relatively thickly dissolved in an organic solvent.

When a solder film is formed on a base metal according to the present invention, the base metal needs to have a higher ionization tendency than tin and lead. The solder alloy does not precipitate from the tin and lead salts of the organic carboxylic acid on the surface of the base metal having a low ionization tendency, so that a solder coating cannot be formed.

Therefore, for example, when the base metal is copper and a metal coating of solder is formed on the surface, copper has a smaller ionization tendency than tin and lead, and therefore, according to the present invention, a coating of solder is directly applied to the surface of the copper according to the present invention. It cannot be formed. Therefore, it is preferable that the surface of copper be plated in advance with a metal having a high ionization tendency, such as zinc or aluminum, and a solder film be formed on the surface according to the present invention.

In order to form a solder coating on the surface of the base metal according to the present invention, the base metal is immersed in an organic solvent solution of the tin and lead salts of the organic carboxylic acid under heating.
The temperature at the time of immersion varies depending on the ratio of tin and lead and the boiling point of the solvent, but when the solvent is squalene, about 250 ° C. is appropriate. The immersion time varies depending on the temperature during immersion, and depends on the thickness of the solder film to be formed, but is about several seconds to several tens of minutes.

When the base metal is immersed in an organic solvent solution of a tin and lead salt of an organic carboxylic acid according to the present invention, the tin salt and the lead salt of the organic carboxylic acid in the solution are decomposed on the surface of the base metal to form metal tin and metal lead. To form a solder alloy, the solder alloy deposits on the surface of the base metal to form an alloy layer, and the newly released solder alloy is combined with the alloy layer to form a solder coating. .

Although the mechanism by which the solder film is formed on the surface of the base metal according to the present invention is not necessarily clear, it is thought to be due to the following process. That is, when the tin and lead salts of the organic carboxylic acid are decomposed, an ion exchange reaction occurs with the base metal, whereby the tin and lead salts of the organic carboxylic acid are converted from the tin and lead salts of the organic carboxylic acid on the surface of the base metal. Lead precipitates, and the deposited metallic tin and metallic lead combine to form a solder alloy, and the solder alloy dissolves in the base metal to form an alloy layer. Further, the metal ions dissociated from the metal salt migrate to the surface of the base metal and repeat the ion exchange reaction to release the metal tin and the metal salt, thereby forming a solder coating layer on the surface of the alloy layer with the base metal.

The organic carboxylic acid, which is an organic component generated by the decomposition of the metal salt, acts as a flux, reduces the surface of the base metal, and promotes the formation of a solder film. In particular, rosin or its derivatives originally have a strong flux action,
It is preferred to use rosin or a derivative thereof as the organic carboxylic acid component.

According to the present invention, a solder coating can be formed by simply immersing a base metal in a predetermined solution, and the operation is extremely simple. Moreover, the metal solder forming the coating is chemically bonded to the organic carboxylic acid, which is an organic component, and does not contain free metal solder particles. Therefore, even when this is applied to a circuit board having a precise circuit pattern, if a circuit board masked with a resist material according to a desired pattern is directly immersed in a solution, it is possible to reliably form a coating according to a fine pattern. It does not cause problems such as lack of coating and short circuit due to free solder particles.

In the present invention, as described above, the metal salt migrates to the surface of the base metal, causes an ion exchange reaction on the surface of the base metal, deposits metal tin and metal lead, and the generated free metal immediately A solder coating is formed on the surface of the metal.
Therefore, there are no free metal particles in the system during the operation, and all the metal components in the solution are used for forming the solder coating. Therefore, even if the content of the metal in the solution is small, the free solder concentrates only on the exposed portion of the base metal on the substrate, and a metal film having a sufficient thickness is formed there,
Extremely efficient.

Furthermore, in the present invention, since the solution is homogeneous and does not contain free solder particles, and a solder film can be formed only on a necessary portion where the base metal is exposed as described above, a component for an electronic circuit can be formed. The present invention can be applied not only to the purpose of bonding, but also to the manufacture of ICs, LSIs, and the like, and can also be used when bonding lead wires to these.

Example 1 Preparation of Tin and Lead Salts of Organic Carboxylic Acids Example 1 Into a four-necked flask equipped with a condenser and a stirrer having a capacity of 1, Chinese gum rosin (acid value: 169, color tone X grade,
Softening point 78 ° C) 175g, 48% caustic potash aqueous solution 63g and water 374g
And a saponification reaction is carried out while stirring at 90 ° C. for 3 hours.
An aqueous potassium salt solution of gum rosin having a pH of 10.5 and a solid content of 30.5% was obtained.

In a beaker with an internal capacity of 2 equipped with a stirrer, 600 g of the aqueous solution of the potassium salt of gum rosin obtained in the previous step and 850 g of water
And diluted with stirring. On the other hand, content 500m
In a l beaker, stannous chloride (38 g), lead acetate (26 g) and water (200 g) were put and dissolved with stirring. The aqueous solution of the metal salt was added to the diluted aqueous solution of the potassium salt of gum rosin, subjected to a metathesis reaction at 30 ° C. for 1 hour, dehydrated and dried to obtain a tin content of 9%.
A tin / lead salt of gum rosin having a lead content of 5.8% by weight and a lead content of 5.8% by weight was obtained.

Example 2 The procedure of Example 1 was repeated, except that tall oil rosin (acid value 168.5, color grade X, softening point 76 ° C.) was used instead of Chinese gum rosin, and the tin content was 8.8. %,
A tin / lead salt of tall oil rosin having a lead content of 5.8% was obtained.

Example 3 The same procedures as in Example 1 were carried out except that asymmetric rosin (acid value 167.0, color tone WG class, softening point 68 ° C) was used instead of Chinese gum rosin, and the tin content was changed. 8.5%,
A tin / lead salt of asymmetric rosin having a lead content of 5.5% was obtained.

Example 4 A 500-ml four-necked flask equipped with a condenser, a drain tube, a thermometer and a stirrer was charged with 300 g of tall oil rosin (acid value: 168, color tone class X, softening point: 76 ° C), and placed on a mantle heater. The mixture was heated and melted while stirring. After melting
Cool to 180 ° C, add 57 g of maleic anhydride, add 190-2
The mixture was heated at 00 ° C. for 2 hours to perform a maleation reaction, and the saponification value was 32.
350 g of a maleic rosin of 4 were obtained.

Next, 175 g of the maleated rosin obtained in the previous step, 120 g of a 48% aqueous solution of potassium hydroxide, and 318 g of water were added to a four-necked flask equipped with a condenser and a stirrer and having a content of 1,
The saponification reaction was carried out with stirring at 90 ° C. for 3 hours to obtain an aqueous potassium salt solution of maleated rosin having a pH of 10.3 and a solid content of 30%.

In a beaker with an internal volume of 2 equipped with a stirrer, 600 g of the aqueous potassium salt solution of maleated rosin obtained in the previous step,
850 g of water was charged and diluted with stirring. On the other hand, in a 500 ml beaker, stannous chloride 69 g, lead acetate 45 g and water 2
00g was added and dissolved with stirring. The metal salt aqueous solution was added to the dilute aqueous solution of the maleated rosin potassium salt, subjected to a metathesis reaction at 30 ° C. for 1 hour, dehydrated and dried to obtain a maleate having a tin content of 17% by weight and a lead content of 12% by weight. A rosin tin / lead salt was obtained.

Example 5 300 g of Chinese gum rosin (described above) was charged into a four-necked flask equipped with a drain tube, a condenser, a thermometer, and a stirrer and having a capacity of 1 and melted at 220 to 230 ° C. to form stannous oxide.
20.3 g and 13.0 g of lead monoxide were added and reacted at the same temperature for 3 hours to obtain a tin / lead salt of gum rosin having a tin content of 5.5% by weight and a lead content of 3.8% by weight.

Example 6 The procedure of Example 5 was repeated, except that the amount of stannous oxide was changed to 10.0 g and the amount of lead monoxide was changed to 6.5 g. A tin / lead salt of gum rosin having a content of 1.8% by weight was obtained.

Example 7 The procedure of Example 5 was repeated, except that the addition amount of stannous oxide was 0.55 g and the addition amount of lead monoxide was 0.4 g. A tin / lead salt of gum rosin having a content of 0.4% by weight was obtained.

Example 8 A 200 ml four-necked flask equipped with a drainage tube, a condenser, a thermometer and a stirrer was charged with naphthenic acid (acid number 22).
4) Charge 125g, raise the temperature to 170-180 ° C, add 10.1g of stannous oxide and 5.9g of lead monoxide, then raise the temperature to 220-230 ° C, react at the same temperature for 3 hours, A tin / lead salt of naphthenic acid having a tin content of 6.3% by weight and a lead content of 3.9% by weight was obtained.

Example 9 The procedure of Example 8 was repeated, except that 90 g of neodecanoic acid was used instead of naphthenic acid as the organic carboxylic acid, to obtain a tin content of 8.4% by weight and a lead content of 5.2% by weight. A tin / lead salt of neodecanoic acid was obtained.

Example 10 The procedure of Example 8 was repeated, except that stearic acid (140 g) was used instead of naphthenic acid as the organic carboxylic acid, to obtain a tin content of 5.6% by weight and a raw content of 3.5% by weight. A tin / lead salt of stearic acid was obtained.

Example 11 A 300 ml four-necked flask equipped with a drain tube, a condenser, a thermometer and a stirrer was charged with 122 g of benzoic acid and 40 g of xylene, and the temperature was raised to 120 to 130 ° C. with stirring to obtain benzoic acid. Dissolved in xylene and stannous oxide
After adding 20.2 g and 11.8 g of lead monoxide, the temperature was raised to 220 to 230 ° C. while dexylene was reacted and reacted at the same temperature for 3 hours. Benzo with a tin content of 11.6% by weight and a lead content of 7.1% by weight was added. An acid tin / lead salt was obtained.

Example 12 125 g of naphthenic acid (acid value: 224), 59 g of a 48% aqueous solution of potassium hydroxide, and 1247 g of water were placed in a beaker having a content of 2 and equipped with a stirrer.
And a saponification reaction was performed while stirring at 30 ° C. for 2 hours.
An aqueous solution of potassium salt of naphthenic acid having a pH of 10.5 and a solid content of 10.2% by weight was obtained.

On the other hand, 38 g of stannous chloride, 26 g of lead acetate and 200 g of water were put into a beaker having a content of 500 ml, and dissolved with stirring.
The aqueous solution of the metal salt was added to the aqueous solution of the potassium salt of naphthenate, metathesis reaction was carried out at 30 ° C. for 1 hour, dehydration and drying were performed, extraction was performed with toluene, toluene was distilled off under reduced pressure of 10 mmHg, and tin content was reduced. 13.2% by weight, lead content 9.2% by weight,
A tin / lead salt of naphthenic acid was obtained.

Example 13 In a 2 beaker equipped with a stirrer, 141 g of oleic acid (acid value: 198), 59 g of a 48% aqueous solution of potassium hydroxide, and 1406 g of water were added.
And a saponification reaction was performed while stirring at 30 ° C. for 2 hours.
An aqueous solution of a potassium salt of oleic acid having a pH of 10.4 and a solid content of 10.1% by weight was obtained.

On the other hand, 38 g of stannous chloride, 26 g of lead acetate and 200 g of water were put into a beaker having a content of 500 ml, and dissolved with stirring.
The aqueous solution of the metal salt was added to the aqueous solution of the potassium oleate, subjected to metathesis reaction at 30 ° C. for 1 hour, dehydrated, dried, extracted with toluene, and toluene was distilled off under reduced pressure of 10 mmHg to obtain a tin content. 12.0% by weight, lead content 8.4% by weight,
A tin / lead salt of oleic acid was obtained.

Example 14 100 g of oleic acid was charged into a 200-ml four-necked flask equipped with a drain tube, a condenser, a thermometer, and a stirrer, and the temperature was raised to 170 to 180 ° C. After adding 2.4 g of lead oxide, the temperature was raised to 220 to 230 ° C., and the mixture was reacted at the same temperature for 3 hours to obtain a tin content of 2.9% by weight and a lead content of 1.8.
By weight, tin / lead salts of oleic acid were obtained.

Example 15 The same operation as in Example 14 was carried out, except that the addition amounts of stannous oxide and lead monoxide were changed to 0.8 g and 0.5 g, respectively, to obtain a tin content of 0.61% by weight and a lead content of 0.39%. By weight, a tin-lead salt of oleic acid was obtained.

Preparation of solution In a 200 ml four-necked flask equipped with a thermometer and a stirrer, 90 g of squalene and the tin / lead salt of the organic carboxylic acid synthesized in each of the above examples were charged, and stirred at 100 ° C for 60 minutes. And dissolved. The amount of the tin / lead salt of the organic carboxylic acid was adjusted so that the content of the tin and lead components in the metal salt in the solution was about 1.4% by weight. Examples 7 and 14
And 15 have a metal content of 0.2
It was adjusted to be 0.05% by weight and 0.05% by weight.

As for the solvent, a high-boiling-point mineral oil (Shellflex # 371, manufactured by Shell Sekiyu KK) was used in place of squalene, and the solvent in which the metal salt shown in Examples and 8 was dissolved was prepared in the same manner.

Immersion of base metal Zinc, aluminum, iron, nickel and copper are used as base metal, and a plate of these metals (30 mm x 30 mm x 0.1 m
m) was immersed in a solution of each of the metal salts heated to 250 ° C. for 60 seconds.

Film thickness measurement The thickness of the metal plate before and after immersion was measured with a micrometer, and the thickness of the metal film adhered to one surface of the metal plate was calculated.

Test results The test results are shown in the following table. In the table, ○ indicates that the film thickness is 3
It shows that it was more than μ. If the coating is 3μ or more,
It is possible to join the base metals by overlapping and heating the base metals on which the coatings are formed.

The symbol △ indicates that a film was formed, but the thickness was less than 3 μm. It is difficult to bond the base metals together as it is, but it is considered that the coating thickness can be increased by extending the immersion time.

X indicates that no film was formed, and it was recognized that a sufficient film could not be formed even if the immersion time was extended.

Short circuit test On the surface of a glass fiber reinforced epoxy plate, two comb-shaped patterns having 10 lines each having a width of 10 mm and a length of 10 mm, the lines having a length of 0.1 m
A test substrate was prepared by printing so as to be alternately arranged in parallel at m intervals. Next, the pattern of the test substrate was plated with nickel, immersed in a squalene solution of a metal salt of Examples 1 and 8 (metal content: 1.4% by weight) at 250 ° C. for about 30 minutes, and a thickness of about 30 μm was applied to the surface of the wire. Was formed.

As a comparative example, paste solder was applied to the test substrate with an applicator and heated to melt the solder, thereby forming a solder coating having a thickness of about 30 μm on the surface of the wire.

Thus, the portion of each test substrate at the line interval was magnified with a microscope, and the presence or absence of a short circuit between the lines was observed.

As a result, on the substrate immersed in the solution of the metal salt of each example, no short-circuited portion between the lines was observed at all, and no continuity occurred even when the current was applied between the two patterns.

On the other hand, in the substrate on which the solder coating was formed by the paste solder of the comparative example, the agglomerated solder particles cross-linked between the lines, and an extremely large number of short-circuit portions occurred. In addition, in some parts, the entirety of the line, including the part of the line and the part of the gap, where the film of the solder and the solder is formed, has occurred.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasutaka Nishi 12-46, Shioichi, Yoneda-cho, Takasago City (72) Inventor Hisao Irie, 423, Kamizume, Yonedacho, Takasago-shi (72) Inventor Tatsuji Mizuta Higashiyama, Hyogo-ku, Kobe-shi 3-18 cho-cho (72) Inventor Shinsuke Ohara 2-3-3 Ibaba-cho, Shimogyo-ku, Kyoto-shi (56) References JP-A-60-96764 (JP, A) JP-A-55-21532 (JP, A)

Claims (2)

(57) [Claims] 1. A solution prepared by dissolving a tin-lead mixed salt of an organic carboxylic acid or a mixture of a tin salt of an organic carboxylic acid and a lead salt in a solvent having a high boiling point. Forming a solder coating on a metal surface by dipping a metal having a large surface area and depositing a solder alloy on the surface of the metal. 2. The method for forming a solder film on a metal surface according to claim 1, wherein said organic carboxylic acid is rosin or a derivative thereof.