CN107911952B - Connection method of power electronic component and printed circuit board - Google Patents

Abstract

The invention relates to a connecting method of a power electronic component and a printed circuit board, which relates to the field of an electric typesetting structure and a production process of power electronic products, and the invention does not use the conventional general welding process any more, but compresses metal pins of the power electronic component and corresponding metal surfaces of the printed circuit board which are required to be electrically connected with the metal pins by a pressure mechanical component in a physical pressure mode to form electric connection. The invention can achieve the purpose of realizing electric connection between the metal pins of the power electronic components and the target metal surface by only pressing external force of the press mechanical component without heating the printed circuit board and worrying about damage to the electric components caused by high temperature.

Description

Connection method of power electronic component and printed circuit board

Technical Field

The invention relates to the field of electric typesetting structures and production processes of power electronic products, in particular to a problem of how to complete electric connection of power electronic components.

Background

Modern electronic products basically have more than one circuit board to realize the basic circuits required by the products and complete the functions to be achieved. Electronic devices on circuit boards are basically manufactured by soldering to connect pins of the device to pads or holes on the circuit board to accomplish the electrical connection. This feature is also inherited by the power electronics field, and a number of soldering processes are used on circuit boards within many products TO electrically connect power electronic devices TO other electronic devices or other electrical components in electronic circuits or electrical systems that need TO be electrically connected through copper on the circuit boards, and common solder packages for such power electronic devices used on printed circuit boards include TO220, TO247, TO-3, 1206, 1210, 2012, SOT223, SO8, TO251, TO252, TO263, and various packages for conventional electrolytic capacitors, etc. The power electronic device can be MOSFET, IGBT, SCR or a diode, and can also be various components needing power current on pins such as a resistor, a capacitor, an inductor, a relay, a current sensor chip, a contactor and the like.

The above-described soldering method for completing the connection presents difficulties and problems when the thermal capacity of the circuit board itself is large, because the heating time required for the soldering process is contradictory to the heating time that the sige-based electronic components can withstand.

As shown in fig. 1, the device 1 is a surface mount power electronic device with large heat capacity, the device 2 is a surface mount electronic device with ordinary small heat capacity, and the device 3 is a copper plating with a certain area on a circuit board connected with a bonding pad of the device 1. In order to achieve soldering, the most reasonable process in the current industry is to slowly preheat the whole circuit board by adopting a reflow soldering furnace until a temperature area close to melting of soldering tin is reached, for example, lead-free process circuit board soldering needs preheating and a soldering flux activation area is close to 180 ℃, and then the temperature is raised to 245 ℃ for about 30 seconds and kept for about 5 seconds to promote the melting of the solder paste on the bonding pad to complete soldering. This process and curve is applicable to soldering of ordinary circuit board products, but when the heat capacity becomes relatively large as 3 in fig. 1 becomes larger and thicker, the copper sheet temperature becomes very retarded to follow the hot air temperature in the furnace, which takes several minutes to raise from 180 ℃ to 245 ℃, and the time for which the furnace temperature stays at 245 ℃ to melt solder paste must be lengthened to, for example, 60 seconds, which results in that 2 in fig. 1 stays at 245 ℃ too long as it can quickly follow the temperature of hot air in the furnace, and the inside is likely to be damaged. In order to avoid the situation that the small device such as the device 2 is dead by heating, the heating and melting time and the melting point time of the device staying at 245 ℃ can only be forcibly reduced, and the problem that the welding quality of the device 1 connected with the circuit board 3 cannot be guaranteed is caused, for example, the problem that the welding such as solder balls cannot be carried out due to insufficient temperature of a welding pad or the situation that the insufficient melting exists on the solder paste melting welding is worse.

It must also be pointed out that the idea of separating the power board from the control board does not fundamentally solve the above problems. For example, in the above problem, it appears that it is effective to remove all of the small devices such as device 2 of fig. 1 onto another separate circuit board of generally small thermal capacity, leaving only the power electronics such as device 1 on the circuit board or aluminum substrate such as copper 3 of fig. 1 with large thermal capacity. However, this is only effective in a certain range, because the heat resistance of the device 1 is limited, and the copper sheet 3 must be greatly increased when the power of the product is greatly increased, so that the heat capacity and the thermal time constant of the device are greatly increased, and at this time, although the device 2 is not thermally deactivated, the temperature of the device 1 is too high before the solder on the copper sheet 3 melts, so that the thermal deactivation phenomenon occurs. For example, the electrolytic capacitor with the surface paste is internally provided with liquid, so that the situation that the solder paste on the pins can be melted at the high temperature of 245 ℃ if the solder paste is placed for a few minutes can be obviously predicted, and the liquid is gasified and burst out of the air vent is a necessary condition. Even liquid-containing power electronics such as electrolytic capacitors, such as TO 247-packaged MOSFET devices with internal junction temperatures of 175℃, can only be provided with a maximum withstand capability of 300℃ heat source for 10 seconds at a distance of 1.6 mm from the metal wall of the product, which does not guarantee reliable melting of the solder paste when the thermal capacity of the solder paste contact metal is great.

In addition, there is another situation that in order to reduce the welding difficulty, the width and thickness of the copper sheet can be reduced by performing compromise adjustment on the PCB typesetting wiring, so that the method for solving the welding problem by adjusting the parameters is seemingly effective, but the problem can be transferred to other aspects, such as that the copper sheet near the welding hole on the circuit board can be blown when the high current is suddenly lifted and conducted under a severe working environment, or the pins of the device are loosened at the temperature of welding Kong Ligao to cause electrical disturbance and even discharge and strike fire. If a circuit board with a large heat capacity, such as a 6-layer 2OZ copper thick circuit board, has a large area of tung plating requirements, when welding a device with large current conduction to a welding hole or a welding pad connected to a copper sheet with large area, in order to ensure that the heat of the welding spot can be gathered to the melting temperature of soldering tin, the shape of the welding hole or the welding pad is cross-shaped or flower-shaped, as shown in fig. 2, so that the heat conduction is limited in the welding process, and the welding difficulty is greatly reduced. The 6 in fig. 2 is the copper sheet area on the PCB board where a large current flows, 5 is the through hole for receiving the pin device, and the 4 is marked with a narrower copper sheet position to help soldering, but these positions are just burned out or cause heat accumulation of soldering holes when current is transferred, or cause the soldering spot to become soft under the working strength required by the product.

There are cost considerations in addition to the two above. For high power electronics, relying on the circuit board to complete power delivery suffers from the aforementioned soldering difficulties and copper foil reliability problems, as well as the cost of the circuit board itself. A 6 layer, 2OZ, high Tg circuit board is more than 10 times as expensive per square centimeter as a 2 layer, 0.5OZ, normal Tg circuit board, which is a typical parameter for most normal non-high power electronic circuit boards. This results in cost differences of tens to hundreds of yuan for board areas of hundreds of square centimeters. In addition, the welding processing cost is multiplied with the increase of the heat capacity of the circuit board and the increase of the welding difficulty, because better quality solder paste is adopted, more solder paste is consumed, longer time is spent for preheating and welding, more working procedures and inspection are spent for guaranteeing the welding quality of all welding spots on the circuit board and the integrity of all devices at the end of processing. Similarly for aluminum substrates, the cost of an aluminum substrate with high thermal conductivity and high dielectric strength as an intermediate layer is several to tens of times the cost of the aforementioned FR4 substrate circuit board.

In summary, when the power density of the product reaches a certain level, how to reliably solder a large number of commercial power electronic components based on the PCB to a corresponding high-power PCB has a problem of reliability, and how to make the PCB layout based on the components work is also a troublesome problem, and in addition to the consideration of cost, if the technology can make the connection when using the components, the connection is convenient and reliable, and meanwhile, the cost is low, so the practical value of the technology is necessarily great, especially under the goal of mass production of reliable products.

Disclosure of Invention

Aiming at the defects of the prior art for realizing electrical connection of power electronic components, the invention provides an electrical crimping method of the power electronic components, which is suitable for pin type components on a PCB and surface-mounted type electronic components.

The technical scheme of the invention is as follows: and the metal pins of the power electronic component and the target metal surface form physical contact to realize electric connection through the pressure mechanical component.

The present invention features that the metal pins of power electronic component and the corresponding metal surfaces of printed circuit board to be electrically connected are pressed to form electric connection via pressure mechanical parts rather than conventional welding process.

The invention can achieve the purpose of realizing electric connection between the metal pins of the power electronic components and the target metal surface by only pressing external force of the press mechanical component without heating the printed circuit board and worrying about damage to the electric components caused by high temperature.

The invention has the beneficial effects that: the volume and heat capacity of the metal body to which the target metal surface belongs can be large and are no longer subject to the welding process. This is very attractive for high current density applications, which can improve product performance from an electrical and thermal point of view, respectively. The electrical angle is that when the volume of the metal body relative to the PCB or the aluminum substrate is large, the equivalent resistance on the path from the metal surface to the subsequent electrical connection can be very small, so that the heating power is obviously reduced; the thermal angle is that the shape of the metal body can be large in volume and area which is very favorable for heat conduction, and the metal body cannot cause the problem that copper sheets on a PCB burn out.

The invention is particularly suitable for specific packages of power electronic components, such as TO220, TO247, TO-3, TO-39, TO251, TO252, TO254, TO257, TO258, TO262, TO263 and TO264, because the power density is relatively large, and the prior welding method is difficult TO use and is unfavorable for production.

Further, in order to prevent a gap from occurring between a metal pin and a target metal surface due to a decrease in mechanical external force of a pressure mechanical part during use of a product and a resistance from becoming large, the invention provides an elastic material on the back surface of the metal pin of a power electronic component far from the target metal surface. Through the buffer capacity of the elastic material, the metal pins and the target metal surface can be ensured to be in close contact and electric connection all the time, and the structure has elastic deformation of the elastic material to ensure good pressure between the metal pins and the metal contact surface under mechanical vibration.

The elastic material is generally a material such as silicon rubber and a synthetic material of the elastic material and other auxiliary materials such as glass fiber, and the Shore A test hardness of the elastic material is generally below 100. The hardness makes the elastic material possibly to be embedded into the elastic material to cause the tearing of the elastic material due to the fact that the elastic material is excessively deep when the elastic material is contacted with the metal pins, and in order to prevent the problem, a thin sheet is arranged between the elastic material and the metal pins of the power electronic component. The contact area between the thin sheet and the elastic material is enlarged, so that the pressure is reduced, and the elastic material is kept intact.

The above sheet may be a metal sheet that deforms and fills the void on the target metal surface under mechanical external force, thereby increasing the conductive area and reducing the contact resistance. Other materials such as a thin plastic sheet may be used when pressure and temperature requirements are not high.

When the surface roughness of the target metal surface is not high enough, the invention also arranges a metal gasket between the metal pin of the power electronic component and the target metal surface. As long as the thickness of the metal gasket is proper, the metal gasket can be deformed under the applied pressure to fill most of the gaps, the measure can greatly increase the required conductive contact area and heat dissipation contact area, and reduce the requirement of surface roughness, so that the metal gasket has more operability.

In addition, if the sheet deformed under mechanical pressure to fill the voids on the surface of the target metal surface cannot completely fill the voids, the invention also applies conductive paste on the surface of the metal pins of the power electronic component or the target metal surface. Contact resistance can be further reduced and heat transfer capability can be improved. Conductive paste is a lipid mixture doped with a large number of fine conductive metal and oxide particles, commonly found in bus bar connections of electrical power systems.

Also, the problem of roughness of the contact surface is considered because if the pins of the electronic device are pressed against a very rough target metal surface, even if the pressure is good, the contact resistance is large because the actual contact points are few. In addition, considering the problem that some target metal surfaces are easy to oxidize, the problem that the contact surfaces are gradually filled with non-conductive oxide is caused by the oxidization of the contact surfaces. Therefore, the invention can also provide a smooth surface metal coating on the surface of the target metal surface. To increase the reliability of contact, the contact resistance can be effectively prevented from becoming worse at the later stage of use.

The invention has certain universality on the physical shape of the power electronic device for completing the required connection, and can realize the connection under the original state of the device after the device is produced, and can also realize the connection after adopting the measure of bending deformation on the pins relative to the original state.

The metal pins of the power electronic component are generally straight, and in order to make the corresponding pins contact with the target metal surface, the metal pins of the power electronic component can also form physical contact with the target metal surface after being bent. Such a measure may simplify the mechanical structure that forms it and the target metal surface extrusion.

The press mechanical component is a bolt and a matched nut, screw holes are formed in the periphery of the target metal surface, and the bolt penetrates through the screw holes. The pressure mechanical part has good universality, is convenient to produce and process and is convenient to assemble.

Drawings

Fig. 1 is a schematic diagram of a conventional soldering process where copper plating on a circuit board is attached to a large heat capacity power electronic surface mount device but not to a small heat capacity common surface mount electronic device.

Fig. 2 is a schematic diagram of a weak position of a copper sheet in a high current caused by a PCB pad pattern for reducing soldering difficulty in a conventional soldering process.

Fig. 3 is a schematic structural view of a through-hole electronic device.

Fig. 4 is a schematic diagram showing the positional relationship of the pins of the through-hole electronic device of the present invention after being bent and pre-processed, and before the press-connection is completed by bolts.

Fig. 5 is a schematic diagram of a basic implementation method of completing electrical connection after bending pretreatment of pins of a through hole electronic device according to the present invention.

FIG. 6 is a schematic representation of a construction of the present invention with a foil protecting elastomeric material.

Fig. 7 is a schematic view of a structure of the present invention with metal shims.

Fig. 8 is a schematic view of a structure of the present invention of a metal body having a plating layer.

Fig. 9 is a schematic diagram of a basic implementation method for completing electrical connection in a factory state where pins of a through hole device of the present invention are not subjected to bending pretreatment and remain in an original factory state.

Fig. 10 is a top view of fig. 9.

Fig. 11 is a schematic diagram of a basic implementation method of the surface mount device of the present invention to complete an electrical connection.

Fig. 12 is a top view of fig. 11.

Fig. 13 is a sectional view of fig. 11 taken along bolts 44 and 45 and cut toward the circuit board.

Detailed Description

Figure 5 shows a connection method which is the most basic of the invention.

The metal frame face 7 of the TO220 or TO247 packaged MOSFET in fig. 3 is physically integrally connected TO the drain D pin inside the package with metal, typically copper alloy material plated with nickel on the surface, and the MOSFET is provided with a straight source S pin 8.

As shown in fig. 4 and 5, metal bodies 11 and 12 are provided on both sides of the power electronic component a, respectively, and the straight source S lead 8 is bent to form a U-shaped source S lead 9, which can be pressed onto the surface of the metal body 12 to be electrically connected. Elastic material 10 is arranged between the U-shaped source S pin 9 and the plastic package shell of the MOSFET, and the elastic material fills mechanical gaps during fixing, corrects assembly errors and resists vibration.

The elastic material of the invention is a material which is not easy to generate permanent plastic deformation, such as natural rubber, silica gel, nitrile rubber, chloroprene rubber and the like, and specifically selects a synthetic material which also needs to consider factors such as working temperature range, pressure and the like, and can also consider a plastic component or glass fiber component.

It is generally necessary to provide at least two pairs of through holes 13 in the metal bodies 11 and 12, respectively, avoiding the power electronic component a, by penetrating bolts 14 in each pair of through holes 13 and screwing with nuts, so that the power electronic component a is clamped between the two metal bodies 11 and 12 by a sufficient mechanical external force. As long as this mechanical external force is kept at a sufficient strength throughout the operation, the electrical contact effect between the U-shaped source S lead 9 and the metal body 12 can be comparable to the soldering effect.

The metal body 11 is connected to the electrical connection pad set 16 by a screw, and the metal body 12 is connected to the electrical connection pad set 17 by a screw. The cable appliances of the user can be introduced easily by means of the electrical connection pad sets 16 and 17. The following circuit connections can be realized: one cable electric appliance introduced into the user is conducted with the metal body 11 through the electric connection piece suite 16, the metal body 11 is conducted with the metal frame surface 7 of the power electronic component A, the U-shaped source electrode S pin 9 of the power electronic component A is conducted with the metal body 12, and the metal body 12 is conducted with the other cable electric appliance introduced into the user.

Although fig. 5 shows only one MOSFET, the structure of fig. 5 can be easily extended to realize parallel connection of a plurality of MOSFETs, and when the number of parallel connection increases, the operating current increases, and the advantages of the present invention become apparent.

Fig. 6 shows the joining method with the metal foil 18 added. The metal sheet 18 is also arranged between the elastic material 10 and the U-shaped source S pins 9, the condition that the U-shaped source S pins 9 which are relatively narrow are deeply embedded into the elastic material 10 under pressure can be improved by the metal sheet 18, and under the same pressure requirement, the metal sheet 18 forms a relatively wide surface pressure surface on the elastic material 10, so that the pressure is reduced, and the possibility that the surface of the elastic material is torn, broken and cracked is greatly reduced. Note that the foil 18 is of a small thickness allowing it to deform under pressure levels to correct the mechanical errors required for fastening.

The above foil 18 may also be replaced by a plastic foil when the pressure and temperature requirements are not high.

Fig. 7 shows a method of joining copper sheets to fill voids in the target metal surface.

When the surface roughness of the metal bodies 19 and 20 is not high enough, the surfaces of the metal bodies 19 and 20 and the metal frame surface 7 are not flat when they are in contact with the U-shaped source S leads 9. At this time, it is considered that the metal gasket 21 is added to fill the gap between the metal frame surface 7 and the metal body 19, the metal sheet 22 is added to fill the gap between the U-shaped source S lead 9 and the metal body 20, and as long as the thickness of the metal gaskets 21, 22 is appropriate, the metal gaskets can deform under the applied pressure to fill most of the gaps, so that the measures can greatly increase the required conductive contact area and heat dissipation contact area, reduce the requirement of surface roughness, and make the technology of the invention more operative.

Fig. 8 shows the connection method after the plating layer is added to the target metal surface. The minute pits on the metal body 20 accumulate detached oxides under the long-term vibration micro-friction, and the oxides are nonconductive in most cases, for example, naturally-occurring oxide films of aluminum metal surfaces under air are nonconductive, so that side effects are brought about on the effect of the extrusion instead of welding aimed at by the present invention, mainly increasing contact resistance. At this time, the metal surface can be protected by a process of plating nickel on the metal body 20 with chrome or other metal plating, and the phenomenon that the nonconductive oxide fills the minute pits can be reduced, maintaining a small contact resistance and high reliability. In fig. 8, the plating layer 24 is provided on the side of the metal body 19 in contact with the metal pad 21, and the plating layer 23 is provided on the side of the metal body 20 in contact with the metal pad 22.

Note that the metal pad 21 or 22 may not be provided, and the plating layer 24 or 23 may be directly in contact with the MOSFET metal frame surface 7 or the U-shaped source S lead 9.

Figures 9 and 10 show one method of attachment when the pins are not bent, with both side view 9 and top view 10 showing the same attachment configuration.

The metal frame face 7 of the MOSFET device B is fastened to the metal body 30 by means of screws 27 to complete the electrical connection between the drain of the MOSFET and the metal body 30; meanwhile, the pin 8 of the MOSFET is not required to be bent, but is directly pressed and contacted with the metal body 31 through the screws 28 and 29 and the metal pressing sheet 25, so that the electrical connection of the source electrode of the MOSFET to the metal body 31 is completed. The insulation sleeve is wrapped around the remaining 2 pins of the MOSFET, except for the 8 pins, to ensure electrical insulation, while the circuit board 24 is used to solder and guide the remaining 2 pins into the desired electrical control loop, note that the soldering involves only weak signal soldering without any difficulty. In fig. 9 and 10, 47 is a welding point.

Figures 11 and 12 illustrate a basic method of attaching a surface mount device.

The control signal pin (G) 36 of a packaged MOSFET such as DPAK or D2PAK is also soldered to a circuit board 37 by conventional means to pass and introduce control circuitry to effect control of the device. The circuit board 37 is separated by an insulating material 38 to realize electrical isolation between the circuit board 37 and the metal body 33; while the metal body 33 is the target of the high current pin (S) 35 that needs to be electrically connected; the pins 35 to 33 can be pressed by the elastic filler 41 and the metal pressing piece 39 through the screws 44 and 45, and meanwhile, the overlapping area of the metal body 33, the pins 36 and the circuit board is a hollowed area which is machined in advance, so that the thicknesses of the circuit board 37 and the insulating material 38 can be just contained, and the pins 36 can be prevented from being bent relatively by a large angle when the pins 35 are pressed, so that the pins 36 are prevented from being damaged and broken off from the root parts of the pins. On the other side, screws 42 and 43 are fixed to the metal body 32, pressing the metal pads 40 and the elastic filler 41 onto the other high-current conductor (D) 34 of the electronic device, and allowing the pins 34 to complete the electrical connection to the desired metal body 32.

Fig. 13 is a sectional view of fig. 11 cut along the bolts 44 and 45 toward the circuit board, showing technical details of the hollowed-out area of the metal body 33. It can be seen that the left part of the metal body 33, which is in contact with the pins 35, is higher than the right part thereof corresponding to the pins 36, the left and right boundaries being in the middle region of the pins 35 and 36.

Claims (1)

1. A connection method of a power electronic component and a printed circuit board is characterized in that a physical contact mode is formed between a metal pin of the power electronic component and a target metal surface through a pressure mechanical component to realize electric connection;

The press mechanical component is a bolt and a matched nut, screw holes are formed in the periphery of the target metal surface, and the bolt penetrates through the screw holes;

Arranging an elastic material on the back surface of the metal pin of the power electronic component far away from the target metal surface, wherein the elastic material is arranged between the metal pin of the power electronic component and the shell of the power electronic component;

A sheet is also arranged between the elastic material and the metal pins of the power electronic components, and the sheet is a metal sheet or a plastic sheet;

a metal gasket is arranged between a metal pin of the power electronic component and the target metal surface;

A metal coating with a smooth surface is arranged on the surface of the target metal surface, and the metal coating is arranged on the contact surface of the metal pad and the target metal surface;

coating conductive paste on the surface of a metal pin or a target metal surface of the power electronic component;

after the metal pins of the power electronic component are bent, physical contact is formed between the metal pins and the target metal surface;

two pairs of through holes are respectively formed on the metal bodies avoiding the power electronic components, bolts are penetrated into each pair of through holes, and nuts are screwed, so that the power electronic components are clamped between the two metal bodies by enough mechanical external force, and the mechanical external force always keeps sufficient strength in operation.