SE515851C2 - Method for checking and mounting electronic surface mounting components - Google Patents

Abstract

A method of testing and mounting electronic components that are to be surface-mounted. The components include on one side a plurality of contact pads that shall be connected electrically to contact pads on one side of a test board, particularly BGA components and corresponding components. The invention is characterized by applying to the component contact pads (2) a metal (5) which is liquid at room temperature or at an elevated room temperature, in a first method step; lifting the component (1) away from the surface of the metal (5) in a second method step, wherewith part (7) of the liquid metal remains on the component contact pads (2); and bringing the component contact pads (2) provided with the liquid metal into abutment with corresponding contact pads (3) on the test board (4), in a third method step.

Description

lO l5 20 25 30 35 515 851 serns plan. These may be electrically conductive needles that run perpendicular to the plane of the interposer between the BGA component and the test card or anisotropically conductive films.

Furthermore, a few sockets have recently been developed that are connected to the BGA component and the test card, respectively.

All these known techniques have the disadvantage that a high mechanical pressure is required to be applied to the BGA component in order to obtain sufficiently good physical, and thus electrical, contact with the test card.

However, persistent problems often occur in the form of high electrical contact resistance, the presence of parasitic inductance and capacitance. Furthermore, said interposes, anisotropically conductive films and said sockets are expensive to design and manufacture.

The present invention solves the stated problems.

The present invention offers an inexpensive method which requires only a low contact pressure between the BGA component and the test board, which provides low contact resistances and which provides low parasitic inductances and capacitances.

The present invention thus relates to a method for checking and in some cases mounting electronic surface mounting components, which components on its one side have a number of contact points which are to be brought to electrical contact at the end of the contact points on one side of a test card, BGA components and the like and are characterized by, a first step the contact points of the component are caused to be immersed in a metal floating at a room temperature or elevated room temperature, where the depth of the metal is made to be less than the height of the contact points of the surface mounting component, by step the component is lifted from above the surface of the metal, the liquid metal partly remaining at the contact points and in a third step the contact points provided with liquid metal are brought into abutment against the corresponding contact points on the test card.

The invention is described in more detail below, partly in connection with an exemplary embodiment of the invention shown in the accompanying drawing, in which - Figures 1-3 show different steps according to the present method - Figure 4 shows an embodiment of the invention.

Figures 1 - 3 illustrate the present method for checking electronic surface mounting components. The figures exemplify the surface mounting component with a BGA component 1.

The BGA component 1 has on its one side a number of contact points 2, usually consisting of about 60% tin and 40% lead. These contact points 2 must be brought to electrical connection to contact points (Pads) (PCBs) 4 on one side, 3 on a test card, see figure 3.

According to the invention, in a first step, the contact points 2 of the component 1 are caused to be provided with a metal 5 floating at room temperature or elevated room temperature. This is illustrated in Figure 2. It is preferred to dip the contact points 2 in the liquid metal. However, the metal can be applied to the contact points by a method corresponding to a printing process, where for example a cylinder surface containing the liquid metal is rolled over the surface of the component where the contact points are located.

According to a preferred embodiment, the liquid metal is caused to be on a flat surface, such as on a glass sheet 6 or silicon sheet. The depth of the metal on the disc is preferably made to be less than the height of the contact points 2 of the surface mounting component 1, in order to ensure that only the contact points 2 come into contact with the liquid metal 5. In this case, the metal wets the contact points 2.

In a second step according to the present method, the component 10 is lifted up from the surface of the metal, as illustrated in Figure 2, the liquid metal to a part 7 remaining at the contact points.

In a third step, the contact points 2 provided with liquid metal 7 are brought into contact with the corresponding contact points, pads, 3 on the test card 4, as illustrated in Figure 3, the contact points 2 on the component being in good electrical contact with the corresponding contact points. 3 on the test card.

Thereafter, tests of the surface mounting component 1 are performed.

In an optional fourth step, the surface mounting component 1 is lifted, after which the liquid metal 7 is removed from the surface mounting component contact points 2. It has been found that water and a common detergent can be advantageously used to remove the metal 7. The fourth step is selectable due to , as described below, this is not always performed. In a highly preferred embodiment, the liquid metal is gal- (Ga) lium or a gallium alloy.

According to another embodiment of the invention, which, however, is not as preferred for environmental reasons, the liquid metal is mercury (Hg) or a mercury alloy.

Gallium and gallium alloys are present in the liquid phase at room temperature or a slightly elevated room temperature. They also have a low resistivity, namely about 14 microOhm x cm.

For comparison, copper has 1.56 microOhm X cm.

Furthermore, gallium and its alloys are easy to use because they are not hazardous to health or the environment, e.g. due to the low vapor pressure. Liquid gallium has an extremely low vapor pressure, namely only 107 ”dry at 400 ° C.

Mercury has a significantly higher vapor pressure, namely 10 ”dry at 400 ° C. 10 l5 20 25 30 515 851 The table below shows examples of alloys useful in the present context: Table 1.

Melting temperature Powder additive Ga 30 ° C Ag Ga / Sn 16 ° C Cu Ga / In 15 ° C Sn Ga / In / Sn 5 ° C Ni As shown in Table 1, a number of gallium alloys with tin, or indium or both tin and indium have a melting temperature. below room temperature. This refers to alloys with a eutectic composition.

These alloys can also be tailored for viscosity by mixing powdered metal in the liquid alloy. Many different metals can be used for this purpose. Table 1 gives examples of preferred metals in the right-hand column. It is preferred to mix a maximum of 20% by weight of metal powder. By mixing metal powder, a paste based on liquid gallium can be produced in which the contact points are dipped in the manner indicated above. The thickness of the paste on the disc 6 and the viscosity determine how much of the paste sticks to the contact points when they are dipped in the paste.

The table below shows the wetting properties of gallium and gallium-based alloys. lO 15 20 25 30 35 515 851 6 Table 2 Material: Metal Glass Silicon Ceramic Epoxy Wetting Good Good Good Poor Poor properties As shown in Table 2, gallium and a gallium-based alloy wett well, or very well, on metal but poorly on ceramics. materials and epoxy. This is an important property that makes gallium-based alloys ideal for the present purpose, since the contact points 2, 3 on both component 1 and the test card 4 are made of metal while the surrounding material is made of ceramic or epoxy.

Another important property that gallium and gallium-based alloys have is that they are oxide refractory with respect to the oxide that may be present at contact points 2, 3, because gallium forms alloys with the material that the contact points consist of. This means that an extremely good electrical contact is obtained, where the contact resistance is normally less than 1 mOhm.

The above-mentioned parasitic inductance and parasitic capacitance become very low due to the small amount of material at the point of contact between the respective contact point 2, 3.

The above applies in a similar way to mercury. Although for the function of the invention it is not of great importance whether mercury or mercury alloys are used instead, mainly from an environmental and handling point of view. In case mercury or gallium alloys are preferred, silver is used, most measures must be taken due to its high pressure and because mercury compounds are toxic. For example, the method must be carried out in a closed room, where the mercury compounds are disposed of in a way that is acceptable from a health and environmental point of view. According to a preferred embodiment of the invention, the surface mounting component 1 is inserted into a frame 8 which supports the test card 4 to align the surface mounting component 1 in a pre-frame 8 may have adjusted position relative to the test card 4, see Figure 4 a lower part 9 and an upper part 10. The lower part 9 suitably has an inner dimension which corresponds to the outer dimension of the component 1.

The upper part 10 is suitably provided with a cross member 11 arranged to abut against the upper side of the component. By arranging tension springs 12, 13 which with suitable force pull the upper part 10 in the direction of the lower part 9, it is achieved that the component 1 is pressed against the test card with a suitable force to ensure that all contact points 2 have a good abutment against the test card. pads 3.

It was mentioned above that in a fourth step the component is lifted from the test card after the end of the test and that the contact points are cleaned.

According to a second, alternative, embodiment of the invention, the test board 4 consists of a circuit board 4 on which the surface mounting component 1 is finally to be mounted in a predetermined position.

In this case, the first, second and third steps are performed, after which a test of the surface mounting component takes place when it has been placed in said predetermined position. In case the test shows that the component has the intended performance, the component 1 on the circuit board 4 is retained with flux at the contact points 2 and 3, said position is heated to a temperature at which the surface mounting card after which the circuit board with the surface mounting component 2 is soldered to the corresponding contact points 3 circuit board 4. For example, such a temperature is about 200 ° C. During soldering, gallium and gallium alloys will alloy with the material in contact points 2 and contact points 3.

According to a third, alternative, embodiment of the invention, where also the test card consists of a circuit board 4 on which the surface mounting component 1 is finally to be mounted in a predetermined position, a test of the surface mounting component also takes place when it placed in said predetermined position.

According to this embodiment, the surface mounting component is mechanically fixed relative to the circuit board in said position. For example, the fixing takes place by means of a frame as shown in Figure 1, or in another suitable manner. In the event that the testing shows that component 1 has the intended performance, component 1 is retained in said position when using the circuit board.

Thus, no soldering of the contact points 2, 3 takes place, but the liquid metal remains in a liquid state during the use of the component. This design has i.a. the advantages that the component is easy to replace and that the liquid metal at the contact points relieves mechanical stresses in the component and the circuit board as a result of temperature changes.

The present invention eliminates the disadvantages mentioned in the introduction. The present method is inexpensive to use.

The method is very good for testing at high frequency and at high speed due to the fact that the contact resistance, the parasitic inductance and the parasitic capacitance are low.

Furthermore, the method is easy to use because the contact pressure between the contact points can be very low.

A number of embodiments have been described above. However, alloys other than those mentioned above can be used. For example, non-eutectic compounds can be used at room temperature or an elevated one.

Thus, the present invention is not to be construed as limited to the above embodiments, but may be varied within the scope of the appended claims.

Claims (10)

10 l5 20 25 30 35 515 851 Patent claims Method for checking and in certain cases mounting electronic surface mounting components, which components on its one side have a number of contact points which are to be brought into electrical connection to the contact points on one side of a test card, in particular BGA components and the like, k (1) the contact point temperature or elevated room temperature liquid metal (5), where the depth of the metal is brought below the height of the surface mounting (1) contact points (2), (1) is lifted from the metal of the liquid metal to part (7) (2) and in that in a third step the contact points (2) (3) provided with liquid metal remain in a second (5) on the step of the contacting component of the contacting component, the places are brought to abutment (4). against the corresponding contact points on the test card A method according to claim 1, characterized in that (5) is caused to be on a flat surface, (6) a v, the liquid metal such as on a glass sheet or silicon wafer. A method according to claim 1 or 2, characterized in that the liquid metal (5) is gallium (Ga) or a gallium alloy. 4. A method according to claim 3, characterized in that (5) is caused to contain an electro- (Ag), (Sn), the liquid metal risk-conducting metal powder, such as silver tin copper (Cu) or nickel (Ni). Method according to claim 1 or 2, characterized in that the liquid metal (5) is mercury (Hg) or a mercury alloy. k ä n n e t e c k n a d att A method according to claim 5, a V, the liquid metal (5) is caused to contain an electrolyte, that in a first step the component (2) is caused to be dipped in a wide space wherein 10 15 20 25 30 35 515 851 10 hazardous conductive metal powders, such as silver (Ag), tin (Sn), copper (Cu) or nickel (Ni). A method according to any one of the preceding claims, characterized in that the surface mounting component (1) is inserted into a frame (8) supported by the test card (4) to align the surface mounting component (1) in a predetermined position relative to the test card. (4). Method according to one of the preceding claims, characterized in that in a fourth step the surface mounting component (1) is lifted, after which the liquid metal (5) is removed from the contact points (2) of the surface mounting component (1). Method according to any one of claims 1 - 7, characterized in that the test card consists of a circuit board (4) on (1) in that a test of surface mounting component - which surface mounting component is finally to be mounted in a predetermined position, (1) and in that in case the testing shows that the component (1) (4) in said position is heated to a temperature at which the ninth occurs when placed in said predetermined position, the intended circuit board with the surface mounting composite mounting component contact points (2) is soldered to the corresponding contact points (3) on the circuit board. k ä n n e t e c k- (3) on finally to be mounted in A method according to any one of claims 1 - 7, in that the test card consists of a circuit board (1) in that a test of surface mounting component which surface mounting component a predetermined position, nenten (1) occurs when placed in said predetermined position, of that the surface mounting component (1) is mechanically fixed (3) in case the testing shows that the component (1) has intended performance relative to the circuit board in said position and that, then, the component is retained in said position when using the circuit board (3).