JPH03197648A - Lead frame material - Google Patents

Abstract

PURPOSE:To stably obtain a high strength lead frame material excellent in etching characteristic, sealing characteristic, and formability by specifying a composition consisting of strengthening elements, such as C, Si, P, S, O, N, Cr, Ni, and Cu, and Fe. CONSTITUTION:A lead frame material having high strength and high hardness and excellent in etching characteristic, sealing characteristic, and formability can be obtained by providing a composition which consists of, by weight, <=0.015%, preferably <=0.005%, of C, 0.001-0.15%, preferably 0.001-0.05%, of Si, <=0.01%, preferably <=0.003%, of P, <=0.005% S, <=0.010% O, <=0.005% N, 2-15% Cr, 33-55% Ni, further 0.01-5.0% of one or more elements among Cu, Mn, Co, Mo, W, V, Nb, Ta, Ti, Zr, Hf, B, Be, Mg, and Ca, and the balance Fe with inevitable impurities and also providing a structure in which crystalline grain size at the time of the final annealing is regulated, preferably, to <=50mum. By using this lead frame material, the high integration of semiconductor equipment can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a lead frame material having excellent etching processability, sealing property and molding processability, and high strength.

Background technology and its issues> In general, it is known that the characteristics of lead materials in semiconductor devices have a great influence on their performance and costs; Fe--Ni alloys have been favorably used, which have a low coefficient of thermal expansion and exhibit relatively good adhesion and sealing properties with semiconductor elements and ceramics.

However, for example, during the cooling process after the resin molding process in the "LSI plastic packaging process", during mounting on a printed circuit board, and even when subjected to temperature cycles in the usage environment, thermal stress is generated between the resin and the lead material. It is unavoidable that the lead material bends, but if this stress becomes excessive, the lead material
- Even if the package is made of Ni-based alloy (e.g. 42% Ni-Fe alloy), cracks may occur in the package or the adhesive interface may peel off, reducing the moisture resistance reliability of the package. In other words, there is a risk that moisture may infiltrate from the outside through the microcracks and peeling interfaces caused by the difference in thermal expansion coefficient between the mold resin and the lead material, damaging the internal semiconductor elements. Therefore, in order to improve the moisture resistance reliability of LSI, it was necessary to use a lead frame material whose coefficient of thermal expansion was close to that of mold resin.

On the other hand, recently, the above-mentioned types of LSIs have been becoming more highly integrated, and this trend has resulted in further promotion of increasing the number of bins in lead frames used. Since it is advantageous to have a thinner material, lead frame materials with higher strength and hardness than ever before are required to accommodate thinner plates.

In addition, when a lead frame is made to have multiple bins, the pin spacing becomes narrow (and the width of the pin itself also becomes smaller), but in order to cope with this, even more precise etching processing is required. In addition to high strength and hardness, an important characteristic required for lead frame materials used in commercial applications is excellent etching workability, which allows control over the pin width and pin spacing. Ta.

By the way, the etching process for lead frame materials made of Fe-Ni alloys is generally carried out by applying photoresist to both sides of a degreased lead frame material, baking a pattern, and developing it, followed by etching using ferric chloride as the main component. It usually consists of a step of etching with a liquid and then removing the resist. Factors that determine the etching performance at this time include "resist adhesion" and "etching speed," but among these, the etching speed of the material is the most important factor. It is no exaggeration to say that the evaluation of etching workability is largely determined by the etching speed, as it becomes easier to control the pin width and pin spacing formed on the lead frame material.

Therefore, as the degree of integration of semiconductor devices increases, lead frame materials are required to have "faster etching speed (that is, better etching processability)" properties in addition to excellent sealing and strength properties. However, the current situation is that no material has yet been found that has sufficiently satisfactory properties such as etching processability, sealing properties, strength and hardness, and even moldability.

For these reasons, the object of the present invention is to provide a material that has high strength and hardness, as well as excellent etching processability.

Established a means to industrially stably provide lead frame materials that have both sealing properties and moldability and can exhibit sufficient performance even when intended for application to highly integrated semiconductor devices. It was put to do.

Means for Solving the Problems> In order to achieve the above objects, the present inventors have specifically developed Fe-Ni.
-Focusing on the relatively high strength characteristics and low coefficient of thermal expansion of Cr-based alloy lead frame materials, we have further improved its strength, made the coefficient of thermal expansion more similar to that of semiconductor chips and mold resin, and developed the etching process. As a result of repeated research exploring the possibility of significantly improving workability and moldability, we were able to obtain the following new knowledge. That is, (a) In a Fe alloy whose main components are Ni and Cr, if the contents of C, St, and P, as well as the N content, are limited to specific low values, the etching of the alloy is Speed will be noticeably improved.

('b) However, if the above-mentioned alloy contains one or more selected specific elements in a predetermined ratio, it may have a particularly adverse effect on the properties required as a lead frame material. In addition to being able to effectively improve the strength of the material without causing any adverse effects, the addition of the above-mentioned specific elements under careful control of the amounts of Ni and Cr brings its coefficient of thermal expansion closer to that of mold resin and semiconductor chips. It is an extremely effective means.

(C) Also, the crystal grain size of the alloy materials mentioned above has a considerable influence on the strength and formability, but by taking measures to keep the crystal grain size below a certain value, it is possible to increase the number of pins in the lead frame. Not only can a desirable "further improvement in material strength" be expected, but moldability is also improved.

(d) Therefore, while comprehensively adjusting the content of Ni, Cr, C, Si, P, etc. in the alloy with Fe-Ni-Cr as the basic component, or at the same time adding specific alloying elements to this, Furthermore, by adjusting the crystal grain size, it is possible to create a lead frame material that has excellent properties such as strength, coefficient of thermal expansion, sealing properties, and moldability, and also has very good etching processability. .

The present invention was completed based on the above-mentioned findings, etc., and it is based on the above-mentioned findings.
).

Si: 0.001-0.15%, P: 0.0
Less than 1%.

S: 0.005% or less, O: 0.010%
below.

N: 0.005% or less, Cr: 2 to 15%.

Ni: 33-55%, further containing Cu, Mn, Co, Mo+W,
V, Nb+ TatTi, Zr, Hf, B
, Be + one or more of Mg and Ca in total 0.0
By configuring the composition to include 1 to 5.0% and the balance consisting of Fe and unavoidable impurities, it has excellent etching processability, sealing property, and moldability, as well as high strength and hardness. ” is characterized by

In addition, in the lead frame material according to the present invention, a) C content is 0.005% or less.

b) Adjust the St content to 0.001-0.05%.

c) P content is 0.003% or less.

If these conditions are adopted alone or in combination, the effect of improving etching workability obtained will be particularly remarkable, and d) the crystal grain size at the time of final annealing (at the end of final annealing) is adjusted to 50 points or less.

Since strength and formability are further improved and stabilized by these measures, by applying one or more of these as necessary, it is possible to sufficiently respond to the production of multi-pin lead frames. .

Next, in the present invention, the reason why the component composition of the lead frame material is limited as described above will be explained in detail together with the effects of each component.

■ Ni is an important component in determining the thermal expansion coefficient of the lead frame material, and it reduces the difference in thermal expansion with the package during and after sealing, resulting in excellent sealing performance and moisture resistance. In order to ensure strength, it is necessary to adjust the Ni content to 33 to 55%. In addition, Ni has the effect of improving the strength and hardness of lead frame materials, but the Ni content is 33%.
If it is less than that, it will be difficult to secure the desired strength and hardness. Therefore,
The Ni content was determined to be 33 to 55%.

Rainbow Cr is also an important component in determining the coefficient of thermal expansion of the lead frame material, and is also an effective component in improving the strength and hardness of the material. However, the Cr content is 2
If it is less than %, not only will the coefficient of thermal expansion become thicker than the desired value, but it will also be difficult to ensure the desired strength and hardness of the lead frame material.

On the other hand, even if Cr is contained in an amount exceeding 15%, the coefficient of thermal expansion becomes larger than the desired value. Therefore, the Cr content was determined to be 2 to 15%.

Once the C content in the lead frame material exceeds 0.015%, iron carbides are generated, which impairs the etching processability of the lead frame material. Therefore, the upper limit of the C content was set at 0.015%, but since solid solution C also has a negative effect on etching processability, the lower the C content, the better, and it is recommended to suppress it to 0.005% or less if possible. is desirable.

Although Si is an element necessary as a deoxidizer, it is also an element that greatly affects the etching processability of lead frame materials. That is, as the Si content increases, the etching rate slows down and etching processability deteriorates. Therefore, in order to ensure good etching processability, it is necessary to adjust the Si content to 0.15% or less. In particular, in the case of a multi-bin type lead frame material, even better etching processability is required, so the Si content is preferably reduced to 0.05% or less. just,
If the Si content is reduced to a region of less than 00001%, the deoxidizing effect will no longer be observed. Therefore, although the Si content was determined to be 0.001 to 0.15%, it is preferable to adjust it to 0.001 to 0.05% if possible as described above.

Like Si, P is an element that harms the etching processability of the lead frame material if it is contained in excess. The above-mentioned negative effect on etching processability is caused by P content of 0.0.
Since it becomes more pronounced when it exceeds 1%, the P content is 0.
．． It was set as 0.01% or less. However, the P content is 0.003
If the content is reduced to 0.003% or less, the effect of improving etching processability becomes even more remarkable, so it is preferable to adjust the content to 0.003% or less.

If the S content exceeds 0.005%, sulfide-based inclusions will increase in the lead frame material, causing defects during etching, such as pin breakage. Therefore, the S content was limited to 0.005% or less.

If the 0 content exceeds 0.010%, there will be a lot of oxide inclusions in the lead frame material, which will also cause drilling defects during etching, so the 0 content should be reduced to 0.010%.
limited to.

Since the etching processability of the lead frame material deteriorates even if the N content exceeds 0.005%, the upper limit of the N content was set at 0.005%.

CulMn+CoJo, W, V, Nb+Ta, Ti
, Zr, Hf, B + first r1 protrusion button These elements all have the effect of increasing the strength and thermal expansion coefficient of the lead frame material, so they can improve the material strength and increase the thermal expansion coefficient. Type 1 or 2 for the purpose of improving the sealing property by making it closer to that of resin mold.
More than one species can be contained. However, if the total content is less than 0.01%, the desired effect of the above action cannot be obtained, while if the total content exceeds 5.0%, the material becomes too hard. In addition to causing deterioration in molding processability, it also becomes difficult to secure an appropriate coefficient of thermal expansion, so the content of the above components was determined to be 0.01 to 5.0% in total.

As explained earlier, controlling the crystal grain size at the final annealing to 50 m1 or less leads to effective improvement of strength and formability, so it is preferable to control the crystal grain size at the final annealing. It is preferable to take measures to adjust the grain size to 50 IIs or less. Here, the grain size is controlled by the working degree and annealing temperature before annealing.

It goes without saying that this is possible by adjusting the annealing time and the like.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> First, a material prepared by vacuum melting was cast, and after hot rolling and pickling, cold rolling and annealing were repeated, and after the final annealing, cold rolling was performed at a workability of 40%, and further 500%
A cold rolled plate (thickness: 0.15 mm) having the composition shown in Table 1 was produced by subjecting it to strain relief annealing at 1 hour at ℃.

Next, after degreasing these cold-rolled sheets, a resist film is applied, a prescribed pattern is baked and developed, and then an etching process is performed using a ferric chloride solution under the same conditions.
A lead frame for 28 bottles was produced.

For the obtained lead frame, the "outer lead pin width and its variation after etching" were evaluated for "etchability", and the "tensile strength", "Vickers hardness" and "mechanical properties" were evaluated. 1 processability (bending property)" and as an evaluation of "sealability", the presence or absence of cracks was investigated when heat cycles (80'CX60+1nX100 times) were applied after resin sealing. The evaluation of the workability (bendability) was carried out according to a 90 degree repeated bending test (bending radius: 0.15 m).

These investigation results were combined with the grain size at the final annealing to
Also listed in the table.

As is clear from the results shown in Table 1, the materials of the present invention all have sufficient strength and hardness, and exhibit excellent etching, molding, and sealing properties. It can be seen that the comparative materials whose compositions do not meet the conditions specified in the present invention are inferior in any of the characteristics required of the above lead frame materials.

That is, it can be confirmed that the present invention materials 1 to 26 have narrower pin widths and higher etching speeds than the comparative materials under the same conditions. It can also be seen that the standard deviation (S, D,) of the pin width formed by etching is small, and a lead frame product with excellent dimensional accuracy can be obtained.

On the other hand, comparative materials 28 to 30 each have a high content of C, St, and P, so the pin widths formed by etching are wide (and the variation is also large).

In addition, it can be seen that Comparative Material 27 does not have sufficient strength because no component for improving strength or increasing the coefficient of thermal expansion is added, and the coefficient of thermal expansion is also too small, resulting in poor sealing properties.

Comparative material 31 had a high S content, so the bottle broke in the bending test.

Comparative materials 32 and 33 have poor bending workability and poor etching workability because the content of strength improving components is too large.

Comparative material 34 has a very large crystal grain size and a somewhat high zero content, but when the crystal grain size exceeds 50 m or more, sufficient strength (hardness) cannot be ensured. .

Comparative material 35 does not exhibit sufficient strength (hardness) because the content of the strength improving component is small.

(Summary of Effects) As explained above, according to the present invention, it is possible to provide a lead frame material that has excellent etching processability, sealing property, and moldability, as well as high strength and hardness.
This brings about extremely useful effects industrially, such as making it easier to further increase the degree of integration of semiconductor devices.

Claims (5)

[Claims] (1) C: 0.015% or less, Si: 0.001 to 0.15% by weight
, P: 0.01% or less, S: 0.005% or less, O: 0
．． 0.010% or less, N: 0.005% or less, Cr: 2-1
5%, Ni: 33-55%, and further contains Cu, Mn, Co, Mo, W, V, Nb
, containing one or more of Ta, Ti, Zr, Hf, B, Be, Mg and Ca in a total of 0.01 to 5.0%, with the balance consisting of Fe and unavoidable impurities.
High-strength lead frame material with excellent etching processability and sealing properties. (2) The lead frame material according to claim 1, wherein the C content is 0.005% by weight or less. (3) The lead frame material according to claim 1 or 2, having a Si content of 0.001 to 0.05% by weight. (4) The lead frame material according to any one of claims 1 to 3, wherein the P content is 0.003% by weight or less. (5) The lead frame material according to any one of claims 1 to 4, wherein the crystal grain size at the time of final annealing is 50 μm or less.