DEVICE AND METHOD FOR MOUNTING AN ELECTRONIC COMPONENT Field of the invention

The present invention relates to assembly of printed circuit boards, in particular a device and method for positioning and retaining an electronic component on a printed circuit board during assembly.

Background of the invention

Electronic equipment normally utilizes a printed circuit board (PCB) for positioning and connecting electronic components, like integrated circuits (IC) . Typically, the placement and soldering of the ICs onto the PCB is an automated process where robots pick components from storage and place them in the pre-programmed position on the PCB. Printed circuit boards for surface mounted components has flat, usually tin, silver or gold plated copper pads without holes, called solder pads, where the components are to be placed. Solder paste, a sticky mixture of flux and tiny solder particles, is first applied to all the solder pads. After initial placement of all of the components, the PCB moves trough a soldering area where the components are soldered to the PCB. In the soldering area the temperature is high enough to melt the solder particles in the solder paste, bonding the component pins to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed, surface tension automatically aligns the components on their pads.

Some components (e.g. optical sensors) need to be very well positioned with respect to the PCB or to an object (e.g. optical lens) that subsequently will be positioned in front of the component. E.g. an image sensor and an associated optical lens are to be mounted directly onto a PCB. The PCB has mounting holes for the optical lens. If the sensor is not aligned correctly with the mounting holes in the PCB (and hence the optical lens) the picture quality from the sensor will be less than optimal, and time-consuming adjustments might be necessary. Due to the

very small sizes and pin spacing of Surface mounted devices (SMD) manual handling and component-level repair is extremely difficult, and often uneconomical.

During placement of IC components on the printed circuit board and during the following soldering process it is possible for the IC component to move out of its intended position. Even if the IC is glued to the PCB when it is placed on the PCB, it is possible to get misalignment in several directions. As illustrated in figure IA and IB, the IC may be positioned a little off target in both x and y direction, as well as in rotation (the dottet line 34 in figure IA and IB illustrates the perfect position for the component pins) . In addition to this, it is possible for solder to assemble under the pins or soldering points on the IC causing it to be lifted in z direction (up), as illustrated in figure 1C. The IC may well be lifted more in one end than in the other end, resulting in the sensor being tilted as well.

For most ICs, e.g. microprocessors and memory chips, such misalignment would not degrade the performance of the IC as long as the component pins have sufficient contact with the correct solder pads respectively. However, such misalignment will result in severe problems in optical sensor systems. E.g. in systems where an optical sensor and its optical lens are connected to the same PCB, the slightest misalignment of the image sensor will cause severe image deterioration. E.g. if the optical sensor is tilted in respect to the PCB, parts of the optical sensor will be outside the focus plane of the lens .

One way of overcoming this problem is to make arrangements that line up or attach the optics directly to the sensor and not to the PCB. However, this way of dealing with the alignment problem is both expensive and complicated.

There are several examples of different soldering jigs for connectors, switches and different electric devices,

but few of these jigs are intended for electronic components mounted on a PCB.

One device intended for preventing components having pins going trough the PCB from being lifted up during the soldering process, is shown in Japanese patent application JP2002261433. This device has no means for guiding or adjusting the position of the component and can only be used for components with pins going trough the PCB.

Another Japanese publication, JP3038089, describes a jig in the form of a frame to be placed around an IC. This solution is intended for surface mounted components and holds the IC in place in the horizontal plane while soldering. However, the soldering jig described can not secure the vertical position, and is not constructed to guide the IC into its correct position. On the contrary, the cavity of the jig is larger than the IC, and it seems like the jig has to be manually mounted on the PCB.

The soldering jig in Japanese publication JP10084183 is placed over a surface mounted IC. However, it is intended purely for masking the space between the pins of the IC during soldering in order to prevent soldering bridges to build up between the component pins.

Japanese publication JP6334325 shows how a guide pin on the IC and a corresponding tapered part on the PCB can be used to position the IC on the printed circuit board.

Summary of the invention

It is an object of the present invention to provide a jig and a method for manufacturing an electronic device that solves at least one of the above-mention problems in prior art.

The features defined in the independent claims enclosed characterise this device further.

Brief description of the drawings

In order to make the invention more readily understandable, the discussion that follows will refer to the accompanying drawings.

Figure 1A-1C is schematic drawings of an electronic component misaligned respective to its optimal position,

Figure 2 is a schematic drawing of a jig according to one embodiment of the present invention and parts of a printed circuit board,

Figure 3A is a top view schematic drawing of a jig according to one embodiment of the present invention,

Figure 3B is a bottom view schematic drawing of a jig according to one embodiment of the present invention,

Figure 4-6 illustrates other embodiments of a jig according to the present invention,

Detailed description the invention

In the following, the present invention will be discussed by describing a preferred embodiment, and by referring to the accompanying drawings. However, people skilled in the art will realize other applications and modifications within the scope of the invention as defined in the enclosed independent claims.

The present invention includes both a method and the means (a soldering jig) for correctly positioning, and retaining during soldering, an IC or similar electronic components on a printed circuit board (PCB) .

As mentioned above, when electrical components are soldered to a PCB there is a risk that components are misaligned with respect to its optimal position during placing on the PCB or during the soldering process. The misalignment may not be problematic for the electrical connectivity between component pins and soldering pads, but for certain components (such as image sensors) the

misalignment may cause serious problems. Therefore, in order to secure good alignment and position accuracy in all directions (x, y, z) for an electrical component 30 to be soldered to a PCB 31, a jig 10 according to the present invention is used, as shown in figure 2. The jig 10 is designed to position the IC 30 in both x and y direction (sideways, back and forth), in rotation t, and to hold the IC down during the soldering process to make sure that the IC remains parallel to the PCB before, during and after the soldering procedure.

In the following detailed description of the present invention, the term "component pin" refers to that part of metallic conductor of an electrical or electronic component that is joined to the printed circuit pattern, i.e., the component leads, pins, terminals, lugs, etc. The term "pad" as used herein refers to that part of the metallic pattern on the printed circuit to which the pin is joined.

Figure 3A and 3B shows a top view and bottom view of an alignment jig according to one exemplary embodiment of the present invention, as also seen in figure 4. The jig comprises a frame 13, a central body 11, a set of mounting pins 14 and one or a set of supporting structures 12 connecting said central body 11 to said frame 13.

The frame has an opening, confined by the vertical inner surfaces 19 of the frame, having a size and shape corresponding to at least a part of the electronic component to be joined to the PCB. In other words, the inner circumference of said frame 13 is substantially equal to the outer circumference of at least parts of the component to be aligned by the jig, and has substantially the same shape. Substantially here refers to that when designing the jig for a specific component, it must be taken into consideration that the components may have slight deviations in size and shape since it is merely impossible to mass-produce components that are 100% identical. However, the opening in the frame (or the inner circumference of the frame) must be as tight as

possible when fitted around the component (or parts of the component) .

A set of guiding members are associated with the frame to guide a component, or at least a part of the component, into said opening of frame 13.

According to one exemplary embodiment of the present invention, a set of guiding tongues 18 are protruding from the bottom of said frame. The guiding tongues 18 are tapered, creating a slope from the vertical inner surface 19. This embodiment prevents protruding parts of the component (e.g. the component pins) from obstructing or interfering with the frame when aligning.

In another exemplary embodiment of the present invention, the frame itself is chamfered, creating a tapered lower portion 22 (referred to as guiding member) of the frame for guiding the component, or parts of the component, into the opening 19 of the frame.

The Jig comprises a set of mounting pins 14 attached to or being part of said frame 13. The mounting pins are designed to engage with a corresponding set of holes 32 in the PCB, and lock to the PCB.

According to one embodiment of the present invention, the mounting pins comprise a flexible arm 16 with barbs 15, such that when the pins are pushed through the corresponding set of holes the barbs engage with the PCB locking the jig 10 to the PCB 31. Removal of the jig requires the application of pressure to the pins, manually or the aid of tools, to prevent the barbs from engaging with the PCB. It should be noted that any type of semi-permanent or quick-release type of locking pin may be used with the present invention.

Further the pins or the holes may be slightly tapered to ease the entry (or guide) of the pins into the holes. Further, the jig comprises one of more holding member (s) for gently pressing the electronic component down on the PCB, holding it parallel to the PCB and preventing the component or parts of the component from being lifted

during soldering. To ensure a correct fastening of the jig to the PCB and at the same time provide a firm pressure on the electronic component, the holding member (s) are at least partly elastically pliable under the return force from the electronic component when pressed down on it. The holding members would typically interact with the top surface of the component, or parts of the top surface.

According to one exemplary embodiment of the present invention, the holding members are a set of flexible holding arms 20 extending substantially horizontally from the lowest part of said central member 11. The holding arms 20 comprise contact members 21 in the area of said arms distal ends, protruding downwards. The central member and its holding arms are designed such that the holding arms and/or the contact member are at least partly elastically pliable under the return force on engagement with a component. In other words, when the jig is pushed down on a component, the characteristics of the flexible holding arms 20 and/or contact members 21 creates a spring like effect on the component, forcing it against the PCB.

According to another exemplary embodiment of the present invention, the holding members are a set of flexible holding arms 20, extending substantially horizontally from the frame, as shown in figure 4. The holding arms 20 comprise contact members 21 in the area of said arms distal ends, protruding downwards. The holding arms and contact members have the same characteristics as described in the previous embodiment.

According to yet another exemplary embodiment of the present invention, the holding member is a spring 23, or a spring like object, associated with said central member 11, as shown in figure 5.

The central body 11 is stiffly anchored to the frame 13 by one or a set of supporting members 12. Further the central body has a substantially flat top surface. Most pick-and-place machines for electronic components have

placement heads comprising a nozzle for holding a component in place by suction. The substantially flat top surface of central member 11 provides compatibility with traditional pick-an-place machines.

In yet an alternative embodiment of the present invention, the central member 11 acts as holding member 20 and a set of contact members are protruding downwards from the bottom of said central member, as shown in figure 6. According to this embodiment, supporting members 12 are flexible to provide the elastically pliability to the holding member. Since the central member is not stiffly anchored to the frame, this embodiment would require a manual installation or a dedicated pick-and-place machine.

Referring back to figure 2, during the assembly of a PCB, a robot (pick-and-place machine) will pick an IC or other electrical component 30 (e.g. an optical sensor) from a feeder and place it onto the PCB 31. The robot is programmed to place the component in the correct position such that the component pins 33 are lined up with the soldering pads (not shown) on the PCB 31. Typically these soldering pads are covered with a solder paste, a sticky mixture of flux and tiny solder particles, prior to the placement of the component. When the PCB later is heated up the solder particles in the paste melt and bonds the component pins to the pads on the PCB.

The PCB 31 may have guiding/mounting holes 32 in close proximity to the electrical component 30 (in other words in close proximity to the soldering pads for the electrical component), which will later be used to mount an object (not shown) in front of the IC, e.g. an optic lens. Since these holes 32 determine the final position of the object to be mounted, and since the relative position between the electrical component 30 and the object is crucial, the same mounting holes 32 are used as guiding/mounting holes for the jig 10.

According to another embodiment of the present invention, dedicated guiding/mounting holes for the jig 10 are made.

When the IC 30 is placed on the PCB 31 it is possible and likely that it is not 100% correctly lined up with respect to the mounting holes 32. The IC 30 may have been misplaced slightly sideways (x-direction) or slightly back or forth (y-direction) . It can also be slightly- rotated, placed at a wrong angle in the horizontal plane.

Therefore, after the IC is placed on the PCB, the robot picks up the jig 10 from a feeder and places it over the IC. When the robot presses the jig down towards the PCB 31 the mounting pins 14 (or parts of the mounting pins, such as said flexible arms 16) on the jig enters the mounting holes 32 in the PCB 31. The holes 32 are now acting as guiding holes for the jig. The tips of the mounting pins 14 may have a conic shape to easily being able to enter the holes 32 even if the accuracy of the robot is not perfect. After the tip of the mounding pins 14 have entered the mounting holes 32 the jig 10 is pressed further down. Now, if the IC is not correctly- positioned on the PCB 31 the edges of at least parts of the IC 30 will come in contact with the component guiding members 18 of the frame 13. When the jig 10 is pressed further down towards the PCB 31 the guiding members 18 will move the IC 30 into the correct position. Just before the jig is in place the edges of at least parts of the IC will have passed the guiding members 18 and entered the part of the frame having more or less vertical edges 19 (also referred to as the opening in the frame) . The tip of the corner pins 14 have small barbs (or hooks) 15 on the side, and parts of the corner pins may have been cut out to make it easier for the pins to flex (or bend) a little, giving room for the barbs 15 to pass down trough the holes 32. When the jig 10 is in its final position, pushed all the way down on the PCB 31, the barbs 15 exit the holes on the other side of the PCB 31 and locks the jig 10 to the PCB 31.

As the jig is about to be pushed into its final position, the elastically pliable holding member, and their contact members 21, engage with the top surface of the IC 30 and are forced to flex, creating a constant hold-down force

on the IC 30. The barbs 15 on one side of the PCB and the holding member on the other side of the PCB, locks the jig 10 and the IC 30 to the PCB 31. The jig that is now being firmly held down on the PCB and secured by the barbs (or hooks) 15 positions the IC absolutely correctly in x, y and rotation. Further the jig prevents the IC from tilting with respect to the PCB.

The PCB 31 can now be moved through the soldering zone where the solder particles in the solder paste are heated to its melting point . The pins of the IC are bonded to the PCB' s solder pads as the PCB cools down again. During the soldering process the IC is held in position by the jig and it is also pushed down against the solder pads of the PCB, preventing it from being lifted and/or tilted.

During testing and further handling of the PCB the jig protects the IC. When it is time to mount the object (e.g. optic lens) in front of the IC, the jig may easily be snapped off (or removed) by pushing on the barbs 15 (or at least parts of the pins) at the underside of the PCB to release them. The object (e.g. optical lens) uses the same mounting holes 32 as the jig 10; hence the object (e.g. optical lens) is automatically correctly positioned with respect to the IC 30.

According to one exemplary embodiment of the invention, the jig is permanently attached to the PCB. The object may then be mounted on the jig instead of the PCB.

The jig 10 also has other features that secure a safe function. The central body 11 of the jig has a substantially flat and smooth top surface, enabling a robot (or pick-and-place machine) to use a vacuum pickup device to hold the jig 10 during assembly. This central body 11 is also used to press down the jig. To allow the mounting pins 14 to be pressed firmly and evenly down, the central body 11 is connected with the frame 13 of the jig by stiff and strong arms 12 extending from the center out to the frame.

To be able to withstand the high temperature during the soldering process the jig should be made of a heat resistance material, e.g. heat resistant plastic materials like polyimides. The jig may be injection molded in a suitable high temperature polymer material, or Reaction injection molded, or created by any suitable production technique. The jig may also be made of any material withstanding high temperatures, such as metal. It is important that the shape of the jig is not significantly changed during the high temperature soldering, furthermore the support members 12 pressing the IC down needs to maintain proper stiffness.

The jig may have 2, 3, 4, 5, 6, or any number of mounting pins .

The jig according to the present invention positions an IC correctly relative to its soldering pads (if necessary) and holds the IC down during soldering procedures, preventing the IC from getting misaligned both in the horizontal and vertical plane. Further, the jig positions an IC with respect to a set of mounting holes, e.g. for mounting optics or other objects that will be mounted to the PCB at a later stage and needs to be precisely positioned relative to the IC.

The jig can easily be handled (picked and placed) by a robot (pick-and-place machine), and is easily removed (snapped off) when it is no longer needed, either by a robot or manually by a person.

The jig protects the IC during testing and further handling of the PCB.

Further, the jig prevents expensive and time consuming manual correction of faulty soldered ICs, reducing- production cost and increasing product quality.