Abstract:
A process for establishing and maintaining parallelism and balance forces between the surfaces of two bodies, in particular, surfaces to be snuggled against each other for the transfer of thermal energy, includes holding springs for laterally holding one of the bodies against movement transverse to a force direction. Resilient mounting bearings are also provided for resiliently holding the body substantially parallel to the force direction but with all points of rotation for the body being spaced away from the body and preferably laterally of the body. Forces apply between the bodies to establish parallelism. The resilient mounting is adjusted during this static mode to maintain the parallelism for subsequent dynamic modes of operation. During the dynamic modes of operation, the resiliency of the holding and mounting arrangements maintain parallelism and balanced forces even in the dynamic mode.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention in general involves a technique for balancing two bodies with respect to each other, and particular to a new and useful arrangement and technique for balancing parts which are particularly used for transferring thermal energy by means of forced controlled thermal contact. 
     Several procedures and apparatuses are known and used already to perform balanced compensation, but basically do not avoid side displacements and have limitations particularly in the dynamic mode during treatments. 
     A typical example is to allow rotation of at least one body about a fixed center while force is applied. Any such point of rotation, however, creates side-displacement and limits dynamic compensation. The mechanical projection of non-parallel bodies to each other is always shorter than their actual dimensions and therefore requires side displacements during compensation. Using a fixed rotation point at any location requires that one edge of a body forces the opposite edge of this body to move and displace as well. Locating the point of rotation to different points does have effects on such displacements--but cannot prevent it. This is in particular the case if larger compensations are required. 
     SUMMARY OF THE INVENTION 
     This invention refers to a process and apparatus to apply force from a first body to at least a second body so that force is equally distributed. A typical application is to transfer thermal energy from a first body to a second body by means of thermal contact using equally balanced and distributed force within the defined contact/force area or to radiate thermal energy from one body to another body using an equally defined gap created by force controlled spacers. Transferred thermal energy can be equally distributed only by means of equally distributed force and balance. Balancing these bodies, to each other prevents any gap between the bodies even if their surfaces are not parallel to each other initially. 
     Another feature of this invention is to keep side-displacement of the bodies to each other during balancing to a minimum or to eliminate it together. A part or component placed between the bodies should keep its defined position and should not move in uncontrolled directions. Basically, a balancing process applies some unwanted force in other directions as well which may cause displacement force to the bodies and parts. 
     In this invention force is handled using mechanically floating bearings operating in the force direction only and operating without a specific point of rotation and creating no or only little side-displacement. Using pre-adjustment of the invention for prebalancing reduces such displacements further. 
     This invention applies such balanced force in a static mode while force is applied first, and in a dynamic mode, while parts and/or bodies may expand in some areas due to thermal expansions and other reasons. 
     Applying mechanical force and/or thermal energy from a first body to a second body in one or more dimensions is limited by missing conformance of the bodies to each other. Additional tolerances are created by the displacement of at least one body to create force due to tolerances in mechanical bearings and fixtures. Further, parts positioned between the bodies such as a printed wiring board are usually not specified having parallel surfaces. If thermal energy is applied additionally, mechanical expansion may be created depending on the thermal properties of all items. If a part between two bodies should be heated such as by means of thermal contact, thermal energy has to be transmitted uniformly and without being affected by any mechanical static or dynamic changes. Further, any side-displacement or side-force not conforming with the force direction during mechanical and thermal treatment, needs to be avoided. 
     This is the case if a high pin count device with 4-sided leads must be mounted to a printed wiring board using soldering technology, where the required thermal energy is applied by a soldering tool, and transferred to the leads by means of force controlled thermal contact applied to all leads of the part simultaneously. If these requirements are not met, thermal energy is not transferred uniformly to all the leads, causing soldering errors. This uniform application is required in the static mode prior to starting the thermal treatment and in particular in the dynamic mode during the thermal treatment, which causes various mechanical expansions in different areas and therefore additionally reduces surface conformation. 
     If automatic and self-balancing static and dynamic conformation of the bodies and parts is available in an apparatus, a side-displacement during balancing may be created. The projection of a non-parallel surface is always shorter than its real surface dimension. Therefore, any balancing creates a side-force resulting in a side-displacement and shifting of parts. This is an unwanted feature for many applications and would therefore limit or reduce the application of automatic balancing. 
     In this invention, balancing is performed with one or more bodies using a mechanically floating displacement device, preferably with friction-free bearings operating in a force direction only, without having a fixed point of rotation and performing static as well as dynamic balancing. 
     In this invention, balancing may be done basically in two steps to reduce or eliminate unwanted side-displacements as much as possible. Step 1 takes care of non-parallelism in the static mode prior to or while force is applied. This can be done by measurement and pre-balancing using a required correction for a moving and/or fixed device position. A typical operating procedure is to apply force under real conditions, with or without parts attached, and to store the performed static correction for the next cycle. This leaves step 2 to balance dynamic changes of non-parallelism such as those crated by changes in the treated parts caused by applied force and by thermal expansion, resulting in a minimum of side-displacement. Aligning the overall mechanical system performance is therefore included in step 1 and does not affect the dynamic correction. If step 2 requires much correction as well, even this step can be simulated and the data used for automatic pre-balancing, resulting in additional reduction to side-displacement. 
     Because of the mechanically floating bearings used in this invention, applied force is equally distributable during static and dynamic balancing. Using the pre-alignment procedures eliminates side-displacements in the overall mechanical system and leaves only corrections to be made which are caused by dynamic changes during treatments. Since no fixed point of rotation is used, balancing at one particular point or area does not affect other areas. 
     A basic application of this invention is to transfer energy from one or more bodies to one or more parts by means of applied force or radiation, such as used to solder-mount high pin count and fine pitch devices to substrates using thermal treatment. 
     Using pulsed hotbar soldering technology, extremely fine pitch devices can be placed and soldered to substrates by means of force controlled thermal energy transferred from a thermal source to the thermal loads, using liquifying materials (solders) and the required thermal process. Such devices require precise alignment of leads to pads and avoidance of any side force during the soldering process which would create misalignment. The substrate can be a multilayer board with tolerances in its thickness, its parallelism as well as entire different thermal properties along the thermally treated areas, resulting in different dynamic thermal expansions as well as deformation. 
     This invention takes care of such applications and allows for compensation of static as well as dynamic tolerances and changes before and during the process resulting in extremely uniform transformation of thermal energy and close to zero defects in the final parts. 
     The basic requirement of this invention is to perform equally balanced force between bodies and to prevent side-displacement while such force and balancing is applied. Further, such compensation should be done in a static mode while such force is applied as well as in a dynamic mode while force is applied already and the parameters of the device(s) are changed, such as by thermally created mechanical expansion and force sensitive means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 illustrates an ideal relationship between two bodies which are perfectly parallel to each other without the benefit of any compensation system, and representing an ideal prior art system; 
     FIG. 2 shows an unbalanced system of the prior art which allows one body to rotate with respect to another body; 
     FIG. 3a is a configuration conforming to the present invention; 
     FIG. 3b is a view similar to FIG. 3a showing the dynamics of the invention; 
     FIG. 4a illustrates a second embodiment of the invention; 
     FIG. 4b and 4c illustrate a further embodiment of the invention; 
     FIG. 5a and 5b illustrate a further embodiment of the invention; and 
     FIG. 6 is a perspective view showing a further and preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     To perform the required conformation of two or more bodies to each other, mechanically floating bearings are used to allow snuggling of the bodies to each other while simultaneously reducing side-displacements (FIG. 5a and 5b). Using such bearings eliminates any fixed point of rotation and thus, the side-displacements they cause (FIG. 3a and 3b) while performing, in a wide dynamic range (FIG. 3a, 3b, 5a and 5b), the needed compensation. 
     Further reducing the basic side-displacement and therefore applied side-force created during snuggling, this invention uses an additional pre-balancing procedure. This is done either by measuring the conformation of the bodies to each other or by reading and maintaining the performed compensation of real conditions in a pre-alignment cycle (FIG. 4a, 4b and 4c). Such pre-alignment cycle may include the parts to be treated with a thermal cycle as well, such as the parts to be soldered. 
     This fulfilled basic compensation (step 1) may be used for subsequent cycles and such procedure may be repeated again and may include simulated as well real analyzed data for the next real cycle. Additional sensing devices may be included, such as to read force and displacement. Even dynamic data (step 2) may be included. This allows presetting the device for lowest side displacement using static data taken prior to an operating cycle, adding data taken from a simulated cycle as well as a real-cycle and dynamic data available from former operating cycles. 
     To preset the subsequent basic value for compensation for following cycles, mechanical set-screws in the simplest form may be used. Preferably, however, software supported mechanical setting devices are utilized. 
     Another important feature of the invented device is its capability for dynamic compensation (step 2) with no compromise. This allows snuggling caused by applied and changed forces, and thermally caused mechanical expansions and twisting. Since the same system and operation of bearings is responsible, dynamic snuggling will not be different and will create a minimum side displacement, if any. This is supported by the relatively long operating range of the mechanically floating bearings which do not make any difference between static and dynamic snuggling. 
     This invention is explained in the drawings showing typical applications which may supply thermal energy from one area of a body to another area of another body, by means of force controlled thermal contact. 
     The basic system with entirely conforming surfaces is shown in FIG. 1, where 101 represents one body, such as a heated bar with legs, which transfers its thermal energy from its surface 102 by means of thermal contact or thermal radiation, to the other body 103. Uniform thermal contact is required within the entire dimension of the contact area between 102 and 103. This can only be achieved if body 103 is entirely parallel to surface 102. Any non-conforming gap 106 caused by the two bodies not being parallel, will result in non-uniform thermal energy transfer. Transferred thermal energy heats the body 103 and cools the body 102, which causes mechanical expansion (positive or negative) and creates additional dynamic changes in flatness and dimensions. Such a configuration using stiff bodies and stiff bearings has limitations in its ability to uniformly transfer thermal energy by controlled force. It requires a different method for improvement, which is provided by this invention. 
     FIG. 2 shows a well-known basic concept for compensation. Body 201 may rotate using a real or virtual point of rotation 209, if force 205 is applied by the body 201 to body 203. Performed rotation 204 naturally creates a side force 208 and side-displacement 207 compared to body 203, since the projected length of 201 onto 203 is always shorter compared to a conforming alignment. Further, this configuration does not allow compensation for dynamic changes such as those created by thermal treatments. 
     An additional disadvantage of this configuration is the missing pre-alignment capability of body 201 compared to body 203, which may create additional shifting 207 and could add more non-uniform force to this system. 
     Further, setting the shown point of rotation 209 at the center of the surface of body 201, may not be easy to realize. Usually, 209 is located more inside body 201, resulting in even more side-displacement. 
     FIG. 3a and 3b show the basic invented configuration. The supports, points or centers of rotation 310a and 310b, are moved as far as possible laterally out of the center of the body 301, and two rather than one point are used, which may even operate simultaneously and change with dimensions of the levers thus created, which depend on the distribution of the applied force and are created automatically. Such points of rotation may be placed in any real or virtual area and is not limited to the shown example. If forces 313a or 313b are applied, body 301 and its surface 302 may rotate about 310a or 310b using lever arms 301a or 301b respectively, in the directions 314a and 314b. 
     Body 301 is connected by lever arms 301a and 301b of the invention, on bearings 310a and 310b and is kept in its basic position by flexible members 311a and 31lb. These bearings may be folded leaf-springs or air-bearings or magnetically preloaded bearings, and allow body 301 to move only in the direction of the applied force 313c. The basic static position of body 301 is defined by the supports 310a and 310b which may have alignment capability for basic settings. These positions are supported by applied forces, e.g. spring forces 312a and 312b respectively. 
     Applied force 313a to body 301, such as from a non-conforming second body, results in rotating of 302 about the rotation point 310b and radius 314b, lifting arm 301a off from 310a (FIG. 3b). Such movement definitely creates side-displacement of 301 but is a fraction of the displacement shown in FIG. 2 because of the much longer and easier to design lever 301b. 
     As a basic invention, supports 310a and 310b may be adjustable (e.g. mechanically) to preset a basic conformation with another body. Using the preloaded forces 312a and 312b defines its position in the force direction 313c. Forces 313a, 313b and 313c and the force of members 311a and 311b may be matched for lowest side-displacement. 
     Another invented feature in accordance to FIG. 3a and 3b is the ability for dynamic balancing of body 301 in the force direction 313c within a wide operating range. FIG. 5a and 5b help explain these advantages. 
     Body 301 in FIG. 3a or 501 in FIG. 5a respectively may move freely in the force direction without touching any support (310a or 310b) and applies snuggling force to another body 503 shown in FIG. 5a. The realignment does not affect such dynamic movement if the supports are left behind. It is only important to create spaces 523a and 523b allowing free movement of body 501 in the force direction. FIG. 5b shows a case where gap 523a is larger than gasp 523b, due to uneven force. 
     For applications requiring close to zero side-displacement, the advanced invention is explained in FIG. 4a, 4b and 4c. FIG. 4a shows the basic configuration without any force applied to body 401. 412a represents the force spring which allows lever 401a to attach the support 410a held together by frame 415a. 417a is an invented additional force transducer which may read and/or set force 412a. 411a is the bearing to keep the system movable in the force-direction only. 
     In FIG. 4a, frame 415a and bearing 410a are connected to a slide or journal 422a and a blocking device 421a is held by a frame 418a, which also mounts the body 403 to a solid mounting 420a. 409 is a possible simulated point of rotation only to explain this operation, but may be in any location. 
     FIG. 4b shows a typical configuration to perform basic alignment between surface 402 or of body 401 and a body 403b, using force 416a and 416b in FIG. 4a and using the simulated point of rotation 409a. 
     Open the slides 422a and 422b by releasing the devices 421a and 421b. This allows forces 416a and 416b applied to body 401 and 403b through levers 401a and 401b to rotate. This results in snuggling both bodies while the non-force direction will still be maintained with bearings 411a and 411b. After performing such prealignment, 421a and 421b will be activated to clamp supports 410a and 410b in place. FIG. 4c shows the performed dynamic snuggling while forces 412a and 412b are applied and distributed by body 401 to 403c. Forces 416a and 416b are not active anymore for any movement in the force-direction. Similar to FIG. 5a and 5b, body 401 may be lifted-up from supports 410a and 410b to allow free additional dynamic balancing. 
     FIG. 6 shows a typical application of a device which could hold a single heated bar. 601 is an enclosure to hold the entire device together and to keep the moving body 602 air-bearings 608 supplied with air 609 and allowing movement in the force direction 606 only. 604 is a typical design of a leaf-spring allowing body 602 to move in the force direction only. These springs are mounted using screws 605. Compressed air is supplied to the input 608. The required pre-balancing can be made using set-screws 603.