DE4041444C1 - Synthetic resin bolts for fixing semiconductor elements - made in pin shape of material which pulls together and thickens on heating - Google Patents

Abstract

The plastic bolt secures electronic components, partic. semi-conductors, to cooling bodies or base material. It is pin-shaped and of material which when heated simultaneously contracts in the axial direction and thickens. it can be parted off from a continuous roll and provided with a head, and the material can be extruded. The material can be moistened, and stretched when hot and then rapidly cooled. ADVANTAGE - Low cost, and holds items firmly together even when hot. (Previously notified in Week 9145)

Description

The invention relates to a plastic bolt for Ver binding of electronic components, in particular for Attachment of power semiconductor components Heat sinks or base material.

Electronic components are usually replaced by An screw or rivet with metal screws or rivets attached. This procedure is also used for power half conductor used on heat sinks or base material.

Often, however, the flange of the semiconductor must be used be electrically separated from the heat sink, so that one too additional non-conductive spacers between the  metal screw or rivet and the flange of the half conductor must use. This always means an increase effort both on assembly parts and on Assembly time.

A simplification is achieved if instead of Metal screws or rivets made of non-conductive Plastic used. You solve the insulation problem, on the other hand, however, are mostly from one for mass items plastic used, d. H. thermoelastic. At Heating they lose their firmness and begin to flow. However, since power semiconductors are more typical wise very warm, - you should just with a heat sink are thermally connected - are sol Plastic screws are unsuitable for this purpose. they would not be able to make a firm connection.

An immediate way out is for the above te semiconductor heat sink connection on, non-thermo plastic or very temperature-resistant plastics to ver turn. The manufacture of this non-thermoplastic or temperature-resistant plastic screws or rivets would be very complex and expensive, since they are not in the Injection molding processes can be produced. A typi material that would meet these requirements, is PTFE (Teflon).

In addition to the cost, such plastic screw show ben or rivets made of temperature-resistant plastics further disadvantages. When using screws would have to with a screw lock against unwanted Unscrewing a fuse can be made as the Surfaces are typically very smooth. To do this you either use a nut or a counter thread. At a rivet made of a high temperature resistant plastic the problem arises that they are neither mechanical  by hitting the head still thermally by opening melting a head can be easily deformed.

The only method would be a so-called expanding rivet remain that is hollow inside and with a stamp is provided, which is struck in the rivet, whereby the end of the rivet spreads. The disadvantages of this Form are obvious. For one, you need one very complex and expensive manufacturing process to such complicated rivets made of temperature-resistant art to fabricate, on the other hand, space for wrapping against the stamp, which in many cases is not available for tightly-built electronics, and others only clamps to the side, but presses not the components to be connected firmly together. Also the production of very small rivets is practically not possible.

DE 38 36 679 A1 is also state of the art to name in which a method of closing of tubular objects is described, which ever but the problem of creating one here Connection of electronic components only on the edge stirs.

The object of the invention was therefore a plastic bolt zen to create even under higher temperatures non-conductive connection of electronic components det and is simple or inexpensive to manufacture.

This problem is solved in that the bolt body is designed like a pen and made of one material exists that when heated in the axial direction contracts and thickened at the same time.  

Such a material can be in a strand with any Cross-section can be extruded. This is very important multiple cheap manufacturing process available. The material is also relatively inexpensive.

You will choose a special plastic (e.g. poly olefin) currently z. B. in the electronics usual heat shrink tubing is used. The material will shrink like this after extruding hoses pretreated by warming them up stood axially stretching and cooling quickly in this state, so that, after being warmed up again, it turns into axia contraction and thickening at the same time. In contrast, shrink sleeves are stretched radially and keep their length when heated again, reduce but their diameter.

The thickening results in a clamping effect of the Bolzens in the hole that is already next to the axia len tightening the bolt good strength ga guessed. In addition, there will be a protruding part of the bolt also thicken, so that practically a rivet head arises. This can be done on both sides. It however, it is also conceivable to put this bolt in blind holes to use.

The plastic bolt is advantageously used end of continuous material from a roll the.

The fact that the bolt as a continuous material on a Roll can be delivered, you can a very inexpensive ge, but also very convenient for the user Manufacturing, transport or packaging and Ver produce a sales unit, especially since any required  Produce bolt length by simply cutting is.

In an alternative training, the plastic provide a head on one end. Thereby of course you have to pack it as a continuous material waive as long as you want to extrude, but has that Advantage that the bolt is only on one side must warm up, and you hit a stop through the head owns, up to which one the bolt in the holes can be stuck without failing, which makes it easy is to be precisely aligned.

Making a head can be done very easily partial heating of the bolt by the manufacturer happen.

It is suggested the cross section of the bolt to make circular.

Other cross sections are of course conceivable, but there Mounting holes are usually round, too round cross section of the bolt.

In a preferred manufacturing process for the Plastic stud is the material of the stud extru dated.

This manufacturing process has the advantage that can produce endless material without problems and that it can be operated with large flow rates. Other Manufacturing process z. B. the above injection molding would proceed with the manufacture of rivets Offer heads.  

After the extrusion or spraying step pouring is proposed, a so-called networking the material of the bolt. Such Crosslinking of the molecules of the plastic happens for. B. by X-rays, and will cause the Ma receives a so-called shape memory.

Finally, it is proposed that the material of the Bolt stretched in heated condition after crosslinking and then quickly cooled.

By treating the stud material in a sol Chen way the shape of the bolt in which the current state is practically frozen and is only by reheating it to its original find shorter, thicker form.

The following is the production of such a bolt and use in practice based on an example are explained in more detail.

A special material is used as the base material of the plastic bolt be selected plastic, its properties have already been described above. A possible art fabric is polyolefin.

This material is in a strand with any Cross-section to be extruded. The cross section is preferably be round because most holes in those the bolt is to be used round.

After extrusion, the molecules crosslink of the plastic. This can e.g. B. by Be radiation done with x-rays. Other means, like microwave radiation are of course also possible.  

After this networking, the plastic becomes he again warms and elongated by train. This takes its length increases, the cross section or diameter increases however, since the material volume must remain the same. This stretching state remains due to rapid cooling hold. So there is a so-called freezing of the Layers of the molecules to each other instead.

Optionally, the strand can be cut into pieces of certain length be cut and with a head on one side be provided.

The bolt is now ready for use and can be attached to the Be be delivered to users.

This will now be similar to the familiar shrink hose a piece of appropriate length from one strand cut the specified initial thickness, which in the hole in which it is supposed to pinch, fits snugly, and a source of heat e.g. B. Use a hot air gun to hold the plastic to heat bolts.

Due to the heating, the state before the so-called Freeze is restored and the bolt becomes his try original molecular layers (before stretching) restore. So it will increase in length contract and thicken at the same time.

As is well known, this is done similarly with shrink sleeves Lich, they are only stretched in diameter and into the frozen this state, so that it turns out later Heat contract in diameter, however their length is preserved.

Before heating, the bolt is replaced by appropriate Drilling in the electronic components, in particular  through the flange holes of the power semiconductors Insulating washer and a correspondingly large boh tion in the heat sink so that it is on both ends protrudes a bit.

If it is a headless bolt, both protruding sides of the bolt with a hot one air gun to be warmed up, whereupon the warmed up Pinch the ends of the bolt in length and thicken at the same time.

If the bolt diameter is selected before heating, that it just fits in the hole, they fit now the ends of the bolt no longer thickened through the Hole and in this sense form a rivet head each side. The contraction of the bolt body leads that the two parts to be connected, semiconductors flange and heat sink, pressed together and firmly together be connected.

There is another decisive advantage here part of the plastic bolt according to the invention. His country ge, d. H. the length of the rivet created not to be specially adapted. Because the protruding ends will thicken, its length automatically set the correct ge. So you can't choose a bolt that is too long since everything overlaps standing material thickens and forms the head.

The problems encountered so far that when the A plastic bolt starts in operation, to perform its function worse because it becomes elastic, will not happen here right now, son will change when the heat appears on the bolt shaft continue to tighten the bolt, d. H. the tension  will continue to increase and the connection of fixed ma chen.

The plastics to be chosen are high temperature must have stability. Those mentioned as an example Polyolefins have a temperature stability up to 200 ° C, which is the maximum permissible operating temperature temperatures of 150 ° C are sufficient for semiconductors. The bolt its full strength even at maximum loading never lose drive temperatures and it still will a sufficiently large temperature reserve remains.

It is also conceivable that the user is only just before the insertion of the rivet sel sel About forms that he warms it and possibly an additional Compression molding.

Claims (7)

1. Plastic bolt for connecting electronic components, in particular for fastening power semiconductor components to heat sinks or base materials, characterized by a pin-like design of the bolt body made of a material that contracts when heated in the axial direction and simultaneously thickens. 2. Plastic bolt according to claim 1, characterized records that the plastic bolts made of continuous material are separated from a roll. 3. Plastic bolt according to claim 1, characterized records that the plastic bolt at one end are provided with a head. 4. Plastic bolt according to one of the preceding An sayings, characterized in that the cross section the plastic bolt is circular.   5. Plastic bolt according to one of the preceding An sayings, characterized in that the material of the Bolt is extruded. 6. Plastic bolt according to one of the preceding An sayings, characterized in that the material of the Bolzens is networked. 7. Plastic bolt according to one of the preceding An sayings, characterized in that the material of the Bolts stretched when heated and then quickly afterwards has cooled down.