JPS62291951A - Lead frame with oxidation resistant nickel plating resistant to release of solder - Google Patents

Abstract

PURPOSE:To contrive improvement in resistance to release of solder by a method wherein the outside layer of double layer plating is thickly formed. CONSTITUTION:When a soldering work is performed, an Ni-Sn alloy layer is grown on the contact interface between Ni plating and solder, and its thickness reaches 0.1-0.3mum. Then, the alloy layer is increased to 0.3-0.5mum or thereabout by the thermal variation with time after soldering. When the thickness of the alloy layer reaches the interlayer of double layer plating, an interlayer exfoliation is generated due to the stress concentration between layers. Accordingly, the release of solder can be prevented completely by forming the plating thickness of the outside layer thicker than the thickness of 0.3-0.5mum at which the Ni-Sn alloy layer can be grown. Besides, the desired upper limit of plating thickness is 2.0mum or smaller taking into consideration of an economical reason. Therefore, the improvement in resistance to release of solder of the lead frame can be achieved by forming the oxidation-resistive Ni alloy plated layer in the thickness of 0.7-2.0mum.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a lead frame with oxidation-resistant nickel plating that is resistant to solder peeling, and is particularly applicable to semiconductor devices such as ICs and transistors. The present invention relates to a structure in which good soldering properties can be obtained even when heated during assembly, and the soldering parts are configured so that they do not peel off even during heating or bending during other semiconductor assembly processes.

[Prior art] Lead frames of semiconductor devices are made of Cu alloy, 42 alloy,
Fe alloys such as Kovar, pure iron, etc. are used.

When assembling a semiconductor device using these lead frame materials, it is necessary to bond the semiconductor element and the lead frame and to electrically connect the semiconductor element and the lead frame after bonding. In such an assembly process,
Since the lead frame is usually heated to 200°C to 400°C, a strong oxide film is formed on the surface of the lead frame with the commonly used Ni plating, which is difficult to use when wire bonding the lead frame or soldering the leads. cannot obtain satisfactory results.

As a countermeasure for this, Nt--B alloy plating is used as a method of imparting oxidation resistance to lead frames.

However, N1-B alloy plating has a higher processing cost and lower productivity than normal Ni plating, so generally after applying Ni plating, N1-B plating is applied by 0.1
A method of performing two-layer plating with a thickness of about 0.3 pm has been adopted.

As a result of applying two-layer plating in this manner, the oxidation resistance of the lead frame is improved, and problems associated with the formation of an oxide film due to heating in the semiconductor assembly process are resolved.

[Problems to be Solved by the Invention] However, although the problem associated with the formation of an oxide film is solved by applying two-layer plating, on the contrary, the problem of solder removability arises due to the two-layer plating. will occur.

That is, by bending the lead portion after soldering the lead portion, a phenomenon occurs in which the solder layer peels off from the joint portion of the two-layer plating. This phenomenon poses a serious problem of impairing the functionality of the semiconductor device.

The present invention focuses on the above-mentioned problems, and makes it possible to obtain good wire bonding and soldering properties even after being affected by heat during the assembly process of semiconductor devices, and to avoid the phenomenon of solder peeling in the soldering parts. It was created with the purpose of providing a lead frame that does not require a lead frame.

[Means for Solving the Problems] The present invention provides a lead frame in which two plating layers are formed by laminating an oxidation-resistant nickel alloy plating on the outside of a nickel plating film, and the two-layer plating The thickness of the oxidation-resistant nickel alloy plating layer of the outer layer is 0.
．． Solder resistant, characterized by being set at 7 to 2.04 m!
[Related to a lead frame with oxidation-resistant nickel plating that has properties.]

[Function] In order to prevent and improve the above-mentioned problem of solder peeling of parts, the first question is what causes the solder peeling phenomenon.

This is the result of various studies regarding the cause.

Solder peeling is caused by the soldering process and subsequent heat effects.
It was discovered that this is caused by the thickness of the grown Ni-5n alloy. Therefore, as an improvement measure, the thickness of the oxidation-resistant Ni alloy plating on the outer layer of the two-layer plating is made thicker than the thickness of the Ni-5n alloy layer that is generated during soldering and due to the subsequent heat effect. We came to the conclusion that the problem of solder peeling could be solved, and as a result of conducting various confirmation tests, we were able to empirically confirm this fact and succeed in obtaining a lead frame that does not cause solder peeling.

This fact will be explained in detail below.

The mechanism of solder peeling can be analyzed as follows.

When soldering the lead portions, 5n-Pb eutectic solder is usually used, and soldering is performed at a temperature of 230 to 265°C.

In this case, due to the influence of time during soldering, a Ni-5n alloy layer is generated at the contact interface between the Ni plating and the solder, and its thickness reaches 0.1 to 0.3 pLm. Furthermore, the thickness of soldering grows as it heats up over time, and reliability tests (125 to 15
0°C, 16-25 hours), the alloy layer has a temperature of 0.
It is said that it grows to about 3 to 0.5 pm.

This grown alloy layer has physical properties that are significantly different from the Ni plating layer and the solder layer, so when the thickness of the alloy layer reaches between the layers of the two-layer plating, stress concentration in the living room causes the living room 31M.

The above is the mechanism of the solder peeling phenomenon. Based on the analysis of this phenomenon, if the thickness of the outer plating layer is made thicker than the Ni-5n alloy layer can form, solder peeling can be effectively prevented. You will be able to do that.

Next, the thickness of the outer oxidation-resistant nickel alloy plating layer is set to 0.
．． The reason why it is specified to be 7 to 2.0 pm will be explained.

If the thickness of the outer layer in two-layer plating is 0.7 or less, peeling cannot be completely prevented due to the growth of the Ni-5n alloy, as is clear from the explanation of the mechanism of solder peeling phenomenon described above. .

On the other hand, the upper limit of the thickness was specified as 2.07pm because
2. If the thickness exceeds OILm, it becomes a safer region with respect to peeling from the viewpoint of the mechanism of the solder peeling phenomenon described above, but it is not preferable from an economic point of view, so the same thickness was set as the upper limit.

On the other hand, the thickness of the base plating is not specified, as it has been confirmed that it does not affect solder peeling.
It can be said that it is sufficient to set the thickness according to the target plating thickness of the lead frame and construct an economical two-layer plating layer.

[Example] After performing general plating pretreatment using a transistor lead frame between phosphorus deoxidizers, plating with various plating thicknesses was performed using the Ni plating bath described in (1) below, and then oxidation resistance as described in (2) below. Plating with various plating thicknesses was similarly performed using a Ni alloy plating bath to create plating samples with different combinations of various plating thicknesses.

■Nickel plating bath conditions NiSO4-6Hz O:250 (g/1)NiC1
z -6H20: 45 (g/1)H3BO3:
30 (g/l) Brightener: O~2 (cc/1) Temperature: 55°C Current density: 2 (A/am”) ■Nickel-boron plating bath conditions N i S 04 ・6H20: 200 (g/l
)HBO3: 30 (g/l) Trimethylamine poran: 10 (g/I) Temperature:
40°C Current density: 2 (A/drrr') Next, the above sample was heated at 360°C in the atmosphere assuming guiponding.
Heat for 5 minutes and apply Tamura Kaken TF-30 to the lead part.
Soldering was performed at 260° C. for 5 seconds using eutectic solder using flux.

Furthermore, after soldering, the sample was soldered in air at 125℃ for 16H.
r Heating, then bending the lead part (inner radius 0.5m)
m, 90" bending) to check for solder peeling.

The results are shown in Table 1 together with the thickness of the inner layer Ni plating and the thickness of the outer layer oxidation-resistant Ni alloy plating.

Incidentally, the solder peeling condition was determined by the number of test pieces in which peeling occurred after the bending process among the 10 test pieces.

As is clear from the same table, according to the conventional method, the thickness of the outer layer plating is 0.1 to 0.37°Cm, so peeling occurs in all cases, but it is within the scope of the present invention. In all cases, no peeling occurred.

In addition, the thickness of the outer layer oxidation-resistant Ni alloy plating is 2.57z.
At m, no peeling occurred, but significant cracking occurred. This is presumed to be due to the hardness of the oxidation-resistant Ni alloy plating layer.

[Effects of the Invention] As described above, the present invention has the effect that good wire bonding and soldering properties can be obtained even after being exposed to heat and vibration, and the phenomenon of solder peeling does not occur during soldering. This lead frame has the following features, making it possible to provide a more practical lead frame for semiconductor devices.

Claims (1)

[Claims] A lead frame in which a two-layer plating layer is formed by laminating an oxidation-resistant nickel alloy plating on the outside of a nickel plating film, and the thickness of the outer layer of the oxidation-resistant nickel alloy plating layer in the two-layer plating is 0.7~2
．． A lead frame with oxidation-resistant nickel plating that has solder peeling resistance set to 0 μm.