JPH0774458A - Method solder feed to board pad - Google Patents

Abstract

PURPOSE:To facilitate to form a specified quantity of solder needed for securing high reliability, when soldering a semiconductor package to board pads, by cutting wire made mainly of solder, and transferring these to pads for a surface- mount type semiconductor package of a board. CONSTITUTION:After wires are mounted on pads, knife edges 8 formed into a rugged shape fitted to the pad space are erected in order to promote and secure hot melt separation, and so as to conform to a wire of a large diameter. The knife edges are provided in a knife edge constituting substance 9, and its assembly is performed after protrusions being 0.15mm wide and 2mm high are formed by an electric discharge process of SUS 304. After solder wires having length equivalent to a lead row are put on a pad row, the knife edge parts are put on the wire from outside the pads. And it becomes possible to perform hot melt separation of a wire diameter of 0.25mm by infrared heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of preliminarily supplying a minute and required amount of solder to a substrate pad in order to secure the reliability of each semiconductor package and obtain the amount of solder required for soldering. .

[0002]

2. Description of the Related Art Various methods are used for supplying soldering to a substrate pad as described above. It is roughly divided into (1) a method of immersing in molten solder and pulling it up, and a method of blowing hot air at that time (solder leveler)
(2) Solder electrolytic plating method (3) Solder paste printing / transfer method (4) Soldering using a robot. Furthermore, (5) Japanese Patent Publication No. 3-41273,
"Solder sheet and its manufacturing method" (IBM, U., USA)
SA10504), there is a method of forming a pad-shaped solder film on a carrier tape. The claimed constitutional requirement is a method of weakly adhering the solder by using a conductor film having a surface energy which does not immediately get wet with the solder as an opening, which is i) the solder is easily formed by hot dipping, but ii) on the other hand For easy removal (peelability), ii
i) The peeled surface maintains the required solder wettability (wettability)
This is because the necessary requirements such as As this method, a pad-shaped metal is vapor-deposited on a carrier tape, and a solder of several tens of mylon meters is attached to the metal by electroplating. Furthermore, this method is a method of aligning the same carrier tape with the required position of the substrate (supplyability)
As one of the constituent requirements, a transparent carrier tape with a sprocket is claimed.

About these known methods, 0.3 mm
When it is attempted to apply to a substrate having a fine pitch equal to or smaller than the pitch, it has been clarified that when a final LSI is soldered to a pad, a necessary solder amount cannot be obtained.

FIG. 1 shows a QFP type semiconductor package (Qu) having a gull wing type outer lead on a substrate pad.
The cross-sectional shape at the time of soldering ad flat package) is shown. QFP lead 1 width is 0.1m
m, 0.3 mm pitch, the width of the pad 2 on the substrate is 0.12 m
When the lead floating amount 3 is 0.05 mm at the maximum with respect to m and a length of 1.4 mm, the required solder amount is calculated to be 0.0127 mm ³ per lead. When this amount of solder is supplied to the substrate by solder paste printing, the amount of the metal solder in the paste is 50 to 60%. Therefore, the paste volume to be printed is 0.0217 to 0.0254. In the range, this printing amount is the amount obtained by the opening size of a printing metal mask having a thickness of 0.13, a width of 0.14, and a length of 1.4 mm. However, in the soldered state as shown in FIG. 1, the shape, especially the height, of the solder fillet 5 formed on the heel portion 4 of the lead is the same as the conventional QF having a pitch of 0.5 mm or more.
It is lower than P, and more solder is required in terms of reliability. However, this amount is close to the limit obtained from the current metal mask manufacturing and solder paste printing techniques.

Therefore, the shape of the fillet 5 in FIG.
It should be a measure of the amount of solder to be supplied to the lead or pad in the case of individually soldering P, that is, individually. Further, it is necessary to supply the same for each pad, which is a technical difficulty. The practicality of known examples will be examined below.

(1) It is a method of immersing in molten solder and pulling it up, but the achievable thickness is at most 0.015 mm.
Nothing more.

(2) An electrolytic plating method of solder has been announced, but this is due to replacement with a copper pad, and the thickness that can be realized is thin and this method is also limited to 0.015 mm. Next, in the method of electrolytic plating in the solder peeling method, 0.0
Plating of 5 to 0.70 mm is possible, and local plating of the entire substrate or necessary parts can be performed. This method is applied to individual soldering of a fine pitch semiconductor package, and is extremely effective when individual soldering is performed before other components are soldered and the solder printing method is applied to other components. However, it cannot be applied for repair soldering.

(3) The solder paste printing / transferring method is a method of locally printing the solder paste.
Difficult to implement on the pitch.

(4) A method of transferring a solder ball is known as a method of directly forming a solder electrode on a semiconductor silicon chip or a method of supplying a ball onto a pad instead of the method. This application is known as a method of forming a ball at the tip of the wire by the same principle as the so-called Au wire thermocompression bonding method, and bonding while cutting the ball. However, this method requires a time proportional to the number of pads because it is a connection method for each pad, and the equipment is expensive.

(5) It is practically difficult to select an appropriate film which has both solder adhesion and peeling property. In addition, it is necessary to use special equipment for alignment.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of supplying solder to a fine pitch substrate pad,
It is an object of the present invention to provide a method for supplying a sufficient amount of solder by solving the drawbacks of the conventional technique for a semiconductor package having a pitch of 0.3 mm or less.

[0012]

SUMMARY OF THE INVENTION The present invention mainly relates to a method of cutting a solder wire and transferring it to a surface mount type semiconductor package pad of a substrate.

[0013]

According to the present invention, it becomes easy to form a predetermined amount of solder necessary for ensuring reliability in soldering a surface mount type semiconductor package pad, particularly a semiconductor package to a substrate pad, and it is particularly narrow. It facilitates repair soldering in space.

[0014]

EXAMPLE 1 One example of the present invention will be described with reference to QFP in FIG. Flux is applied to the pad 2 and the wire 7 cut to a length corresponding to one side of the QFP lead row 6 is adhered, and then flux is applied and melted and separated by heating with hot air. . The amount of solder per pad supplied by this method will be described with reference to FIG. 3 in terms of a 0.3 mm pitch QFP. That if the wire diameter d, the number n, the at 0.3mm length of melt separation, the volume is supplied to the pad ^{= 0.3n (πd 2/4)} . Therefore, the number is determined by trial calculation in Table 1, and the applicable diameter is 0.17.
It is 5 mm or more. If the wire has a diameter of 0.10 mm or more, it is easily available. Therefore, a wire having a diameter of 0.175 mm or more can be arbitrarily supplied.

[0015]

[Table 1]

The work of straightening the wire into straight lines, cutting the wire into a predetermined length, and aligning it with the pad can be easily performed manually.

An example of a method for heating and transferring a solder wire will be described below. A wire 7 having a predetermined diameter cut into a predetermined length is aligned and mounted on the pad 2, coated with flux, and then heated by hot air to melt and separate each pad. In this case, if the heating is non-uniform, it is drawn to a portion where it is easily melted, and the transfer shape varies, and in particular, a bridge partially occurs. Therefore, it is necessary to find suitable conditions, and Table 2 shows the experimental results for the number of solder diameters.

Regarding the heating experiment in this embodiment, in the experiment using the contact type tool as the heating source, the wire diameters were 0.1 and 0.15 mm, and only one was not bridged, but the number of two was two. In the case of No. 3, a bridge was formed at the part protruding from the tool at the end of the pad, and a small amount was observed even if the tool width was wider than the pad length. The reason for this is that the molten solder protruding from the tool cannot be separated by cooling, and even if the flux viscosity is increased for the purpose of promoting the separation, almost no effect is recognized. Therefore, the heating device uses non-contact hot air or infrared rays (halogen).
Lamp system is essential.

When hot air was used and the diameter was 0.1 mm, melting, separation and transfer were easy, and bridges were not formed up to 3 in a 0.1 mm pitch. This is because the heat capacity is small. The main reason for the generation of bridges is that the solder is heated by hot air, and the molten solder is blown by the air to accelerate contact. Generally, a bridge is likely to occur at the end of the pad. Therefore, it means that it can be prevented by limiting the air volume, and by using an infrared (halogen) lamp type heating device as a heating source, 0.2
No bridge is formed up to 0 mm. However, this embodiment is still insufficient for the intended solder amount.

[0020]

[Table 2]

Second Embodiment Another embodiment will be described with reference to FIG. Generally for the board pad, and also in the narrow space where other parts are placed around the target pad in the repair application,
It is easy to print the solder paste in a single letter. In this embodiment, a thin line of solder paste is printed 8 on the pad row, the solder wire 7 corresponding to the length of the lead row is adhesively mounted using the flux component and the adhesive force of the paste 8, and then the flux is applied. After that, it is heated to melt and separate the wire. In this method, as in Example 1, melt separation was possible up to a wire diameter of 0.2 mm without bridging.

EXAMPLE 3 Another example is a knife edge 8 that is textured to fit the pad gap after the wire has been loaded onto the pad to facilitate and ensure melt separation and to accommodate larger diameter wires. Is to stand up. This embodiment will be described with reference to FIG. In FIG. 5, the knife edge 8 is provided on the knife edge structure 9, and the width of the convex portion is 0.15 mm and the height is 2 m.
Then, SUS304 was molded into the m by electric discharge machining and then assembled. A solder wire having a length corresponding to the lead row was placed on the pad row, and then the knife edge was placed on the wire from the outside of the pad. In this example, infrared heating enabled melting and separation of a wire diameter of 0.25 mm.

Since the use of this method causes flux burn-in, it is necessary to prepare a large number of knife edge constructions 9 and wash them after use.

A practical knife edge structure 9 will be described with reference to FIG. In FIG. 6, around the rectangular body 10 having the same size as the outer shape of the QFP body, the lead 1 (total length 1.3 m
m) A concave and convex knife edge 8 having a length of 2 mm and a width of 0.15 mm was attached 2 mm below the bottom surface of the rectangular body. FIG. 7 is a plan view thereof, but the knife edge structure 11 was constructed so as to be compatible with a commercially available QFP alignment device having the structure shown in FIG. That is, the apparatus shown in FIG. 8 comprises a QFP main body adsorption mechanism section 12 and a head 13 having a hot air blowing port around the QFP main body adsorption section, and is attachable to and detachable from an elevator 14. The QFP lead and the substrate pad are aligned by a method in which a CCD camera inside the prism mechanism 15 captures individual images, the images are individually formed on a video monitor, and the individual images are combined. After that, the structure is such that the position of the XY table 17 on which the substrate 16 is mounted is adjusted to match the individual images.

Therefore, the knife edge structure 9 of FIG.
Like P, it is configured so that it can be easily aligned.
It is very easy to align the knife edge over the wires arranged on the pad row. By this method,
Melt separation of wires up to 0.30 mm in diameter can be achieved without bridges.

As a heating source of the apparatus shown in FIG. 8, equipment in which four small halogen lamps are combined is commercially available, and this equipment can be similarly implemented. Further, the knife edge structure 9 of the present embodiment was formed by electric discharge machining, but as another embodiment, as shown in FIG. 9, a diameter of 0.15 mm formed in an L shape around a rectangular body 10 having an outer shape of a QFP body. It can also be manufactured by a method of embedding a tungsten wire 16 of a certain degree.

[0027]

According to the present invention, it is possible to locally supply an amount of solder necessary for soldering a semiconductor package onto a pad of a printed circuit board to individually solder fine pitch LSI packages. To do. In particular, it is suitable for supplying solder for re-soldering in repair work of an LSI package which is required in a narrow space where other components are soldered.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a QFP package having a gull wing type outer lead soldered on a substrate pad.

FIG. 2 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 3 is a plan view in which Embodiment 1 of the present invention is applied to a soldering pad to which a QFP having outer leads having a pitch of 0.3 mm is applied.

FIG. 4 is a plan view showing a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a third embodiment of the present invention in which knife edges are arranged.

FIG. 6 is a sectional view of a knife edge structure showing a third embodiment of the present invention.

FIG. 7 is a plan view of a knife edge construction for Example 3 of the present invention.

FIG. 8 is a conceptual diagram showing a commercially available repair device with a QFP alignment mechanism.

FIG. 9 is a plan view of a knife edge structure showing another embodiment of the third embodiment of the present invention.

[Explanation of symbols]

 1 ... QFP lead, 2 ... Board pad, 3 ... Lead floating amount, 4 ... Lead heel portion, 5 ... Fillet, 6 ... QFP lead row, 7 ... Wire cut to length equivalent to lead row, 7 '... Wire cutting piece, 8 ... Knife edge, 9 ... Knife edge structure, 10 ... QFP body outline, 11 ... Other type knife edge structure, 12 ... QFP body adsorption part, 13 ... Head, 14 ... Elevator , 15 ... Prism mechanism, 16 ... Tungsten wire.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Nakano 1 Ikegami, Haruoka-cho, Owariasahi-city, Aichi Prefecture Office Systems Division, Hitachi, Ltd. (72) Noboru Kawakami 1-Ikegami, Haruka-cho, Owariasahi, Aichi Hitachi, Ltd. Factory Office Systems Division

Claims (4)

[Claims] 1. A predetermined diameter for the purpose of transferring solid solder in an amount necessary for ensuring soldering reliability onto a pad of a printed board on which a semiconductor package having a fine outer lead pitch is surface-mounted. After cutting the solder wire to a length corresponding to one side of the lead row of the semiconductor package, one or more solder wires are aligned on the pad row to which flux has been previously applied, and then flux is further applied to the wire and the pad. A method of supplying solder to a substrate pad, characterized in that the solder is separated from the solder and transferred to the pad by heating and melting by contacting with. 2. The solder paste according to claim 1, wherein a solder paste is preliminarily printed on the pad in a character form, a solder wire is adhered onto the paste, flux is applied, and heating and melting are performed to separate the solder on the pad, A method for supplying solder to a substrate pad, which is characterized by transferring. 3. The knives according to claim 1, wherein in order to promote and ensure the melting and separating of the solder wire, a knife edge assembly formed in an uneven shape corresponding to the pad gap after the wire alignment is aligned and the knife edge is added. A method of supplying solder to a substrate pad, which comprises applying pressure to form a barrier, and then applying flux to heat and melt to separate and transfer the solder to the pad. 4. The heating according to claim 1, wherein the knife edge structure is a structure having the same outer shape as the main body of the semiconductor package, and the knife edges are formed on four sides of the structure to form a knife edge. A solder supply method to a board pad, which is configured so as to be adapted to a component suction head of an apparatus.