GB2284368A - A circuit board production process - Google Patents

Abstract

A production process (1) for circuit boards includes various steps which are carried out simply and which improve efficiency and quality in the overall process. A computer system cross-references (2, 3) internal and supplier raw material identification data and prints (4) colour-coded labels for raw material for immediate identification of receipt time. The epoxy is applied in a screen printing process (6). Support pillars for the circuit board during screen printing are mounted by use of a guide plate having through-holes, which is removed upon correct alignment of the magnetic support pillars (7). Optical sources and sensors are mounted for detection of mis-alignment of component reel dispensers and a resilient probe is provided for monitoring of incorrect support of an applicator head to prevent damage occurring to it. A very quick change around in manual assembly is achieved by use of rotatable support plates for bins at different stations (15). Burn-in testing (19) is carried out by use of aligned cylindrical sockets and pin probes in which a support rack and burn-in tray slide rails are aligned for effective and efficient connection of the boards to control circuits for burn-in testing. <IMAGE>

Description

"A Circuit Board Production Process" The invention relates to a circuit board production process.

At present, there are available many sophisticated and extremely efficient machines for carrying out various operations in such a production process. An example is a "pick and place" placement machine such as that described in US Patent Specification No. US 5,029,383 (Universal Instruments Corporation). Suction is used for picking of a component and in this case compressed air introduced into a cavity generates an air bearing so that the articulating tip complies with the upper surface of the component. In another example, European Patent Specification No. EP-A1-0,345,061 (Universal Instruments Corporation) describes a feeder drive assembly in which a relatively simple mechanism is provided for adjusting the stroke for different centre-to-centre component distances on a reel. Further, United States Patent Specification No. 5,062,567 (Schlumberger Technologies Inc.) describes an improved lead for surface-mount components which is constructed to provide for easy visual quality control inspection after solder reflow.

Undoubtedly, such equipment and developments generally improve individual operations in a circuit board production process. The invention is directed towards providing an improved production process which relates to all aspects of circuit board production from raw material input to final testing, the combination of improved steps in the process providing for improved efficiency and quality.

According to the invention, there is provided a production process comprising : receiving raw materials; recording data relating to the raw materials, the data includIng a supplier identifier and a cross-referenced internally generated identifier; with reference to real-time data, a printing system printing a label containing raw material data, the label being colour-coded for immediate identification of the time of receipt of the raw materials; retrieving a batch of blank printed circuit boards; mounting the batch of blank circuit boards at the inlet stage of a screen-printing machine and applying epoxy to pre-defined portions of trie board for wave-solder component locations; carrying out screen printing of the board by supporting the board on magnetic pillars, the location of the pillars being set by use of a guide plate having through-holes in which the pillars are initially inserted, the guide plate being pulled upwardly when the pillars are in position on the base plate of the screen printing machine; carrying out component placement operations by use of a rotating turret supporting driven applicator heads, the applicator heads being fed by a set of reel dispensers mounted on a sliding carriage, in which means are provided for monitoring alignment of the component dispensers above the carriage; heating the board by passing it through an oven for solder reflow; carrying out a visual inspection of the surface-mount soldered board; carrying out manual insertion of components on the board; wave-soldering non-surface mounted components; carrying out in-circuit testing of the soldered board and any subsequently required repair work; and carrying out burn-in testing.

In one embodiment, the alignment monitoring means of the component placement machine comprises a light source and a sensor mounted in alignment above the dispenser heads, the sensors being connected to a machine control circuit for cutting power to the applicator heads on detection of mis-alignment.

Preferably, the component placement machine further comprises means for detecting dislocation of an applicator head on the turret of the control circuit for preventing further rotation of the turret on detection of displacement.

In one embodiment, the detecting means comprises a resilient probe mounted just below the circumferential path of the applicator heads, and an electrical limit switch at the base of the probe to detect movement thereof, the limit switch being connected to applicator head control circuits.

In another embodiment, the probe is mounted adjacent to the component application position of the applicator heads.

In a still further embodiment, an inspection step involves recording on a medium data relating to nature and stage of faults, the recording medium being structured for immediate identification of faulty apparatus and faulty raw material such as a circuit board.

Preferably, burn-in testing is carried out on a rack having conductors for transmission of test stimuli and for reception of output signals, the rack having a set of sockets with bores mounted in alignment with the direction of sliding of the rack in the burn-in oven, the burn-in oven having a set of rigid conductor probes mounted in alignment with the bores of the sockets on the rack for engagement with the rack sockets on sliding of the rack inwardly.

Ideally, manual component insertion is carried out at a plurality of stations, each station having a bin support plate mounted for rotation about a central, vertical axis for change-over procedures.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which : Fig. 1 is a flow chart illustrating a production process of the invention; Figs. 2(a) to Figs. 2(b) and 2(c) are diagrams showing a screen printing set-up arrangement of the process; Figs. 3 and 4 are perspective and diagrammatic side views respectively showing operation of a component placement machine and arrangements to prevent damage to important parts of the machine; Figs. 5(a) and 5(b) are more detailed perspective views showing applicator heads of a component placement machine and further arrangements to help avoid damage to the applicator heads; Figs. 6 and 7 are perspective and diagrammatic plan views respectively showing manual component placement stations used in the process: Figs. 8(a), 8(b) and 8(c) are various views showing the manner in which burn-in testing may be carried out efficiently and reliably.

Referring initially to Fig. 1, a production process 1 is illustrated in which steps 2 to 5 relate to the initial stages. Initially, raw materials are received and two sets of data are generated and recorded on computer systems in steps 2 and 3. One set relates to supply data such as the time and date of the raw materials and any data generally which would be of use in later tracking of circumstances in which the goods arrive. The other is supplier data such as supplier identification codes etc.

which is recorded in step 3. In step 4 the computer system generates colour coded labels for each container of raw material, the label including both the supplier identifiers and also an in-house identifier, as appropriate. An important point is that the computer system is configured for recording raw material data using the supplier identifiers so that tracking of components for fault identification may be easily and comprehensively carried out at a later stage. The colour coding of the labels indicate the time and in this case month in which the raw material was received. This provides for quick identification of the correct raw materials to be used at any particular stage.

A batch of printed circuit boards is then selected and mounted at the inlet stage of a screen printing machine which applies epoxy resin at locations for components to be wave-soldered. It has been found that by using a screen printing method for application of the epoxy, efficiency and accuracy of the epoxy application stage is improved. However, an epoxy applicator could alternatively be used.

For application of solder to the board surface mount components, reference is now made to Figs. 2(a), 2(b) and 2(c). A steel base plate 30 mounted on a pillar 31 of the screen printing machine magnetically attracts magnetic support pillars 32 for the board during screen printing.

For each production batch, an individual guide plate 33 having a set of through-holes located at the exact positions for correct relative positioning of the support pillars 32 is mounted on the base plate 30. The support pillars 32 are placed through the through-holes of the guide plate 33, which is subsequently removed by moving upwardly away from the pillars 32 until a stage as shown in Fig. 2(c) where the circuit board is conveyed into position above the pillars 32 and screen printing commences. As shown in Fig. 2(c), screen printing is carried out by presentation of the screen printing stencil 37 to the circuit board 36 and application of solder paste by a hard plastics squeegee 38 controlled by a control head 39. The setup operation of the support pillars 2 is extremely simple and it has been found that it is of considerable benefit in improving quality of the screen printing operation as it leads to the boards being supported in the correct manner for both stability and also positioning relative to the template 37. These steps are indicated by the numerals 7, 8 and 9 in Fig. 1.

The next stage of the production process involves component placement to one or both sides of the board 36.

A component placement machine of the "pick-and-place" type is used as shown in Figs. 3 and 4. The machine 40 has a support frame 41 which forms a pair of rails 45 onto which component reels 42 are mounted for movement in the longitudinal direction. There is also a set of peel-back film reels 43 mounted on carriages 44 sliding on the rails 45. kn important aspect 0: the invention is an arrangement whereby a light beam source 47 generates a light beam 48 which is aligned just above the surface of the support carriage 44 for the reels 43. As shown in Fig. 4 the pick-and-place applicator head 50 approaches very closely to the dispensing end of the carriage 44 and accordingly mis-alignment of the carriage 44 could cause the applicator head 50 to collide with it and be damaged.

As the applicator head mounted on the applicator turret is an extremely important and sophisticated item of equipment, the use of the light sensing arrangement 47 is extremely important in avoiding damage to the component placement machine. A light detector, (not shown), is mounted at the far end of the support frame 41.

As shown in Figs. 5(a) and 5(b), another important aspect of the invention is the manner in which damage to the applicator heads by breakage or displacement of a support bar is avoided by use of a probe sensor 52. The applicator heads 50 rotate and move in a vertical direction by sliding of a component in a helical slide on the turret. The lowest position for an applicator head 50 is during actual component placement. Following component placement the applicator head rotates and moves upwardly in a sharp action to make way for the next applicator head 50. The probe 52 is mounted in the potential path of the applicator head 50 if it were to rotate with the turret but not move upwardly in the slide which guides its movement. If this were to happen the probe-52 which comprises a resilient coil spring supported probe member 53 mounted on a microswitch base 54-would trigger an alarm signal preventing for further movement of the applicator heads 50. Such a scenario is shown in Fig. 5(b) in which deflection of the probe 52 is shown. While this arrangement is extremely simple, it has been found that it would be extremely effective in preventing severe damage to the omponent placement machine. Operation and alignment of the real dispensers is indicated by the step 10 and component placement by step 11.

In step 13 solder reflow is carried out by conveying the board through a reflow oven at the appropriate temperature. Step 13 involves a 100% inspection step immediately following solder reflow and re-work through the reflow oven dependant on the inspection. The 100% inspection involves inspection for coplanarity, solder quality, and correct components. A record is made at this stage of all faults which are detected. Faults are recorded in a grid arrangement whereby each row of the grid relates to a particular fault, the rows being arranged in groups for the major production stages. The columns of the grid relate to boards, there being one column for each circuit board. In this way, inspection of the quality control record will immediately show whether problems are arising for a particular production operation, or if they are indeed concentrated on a particular set of boards for a number of operations in which case a bad quality raw material batch could be suspected. These steps are indicated by the numerals 13 and 14 in Fig. 1.

Following solder reflow and quality inspections, manual assembly is carried out in step 15. Referring to Figs. 6 and 7, an arrangement is shown whereby there may be very quick batch changeovers from manual assembly. For manual assembly there are three-work stations shown, each of which has a rectangular bin support 60 having apertures 61 for support of the bins 62. The supports 60 are mounted alongside a conveyor belt 63 mounted on a support frame 62. Each station may relate to a particular batch of circuit board production and the number of available stations which are pre-set up is multiplied by two by an arrangement whereby each support 60 may be rotated as shown by the arrows 65 in Fig. 7 to present a different setting arrangement of bins to the operator at the conveyor belt 63. While this is a simple feature, its contribution to the overall production process is significant in that is prevents a bottleneck arising at the manual production stages and more importantly it prevents quality problems arising by the mounting of wrong bins, or the mixing of components.

As indicated by the steps 16 and 17, wave soldering and in-circuit testing are then carried out followed by repair in step 18 dependent on the output of the in-circuit tests.

In step 19 burn-in testing is carried out as illustrated in Figs. 8(a), 8(b) and 8(c). A burn-in testing tray 70 is used for at least some batches of circuit boards, the tray 70 having supports 71 for the circuit boards 72. The tray 70 incorporates conductors 73 leading to sockets connecting with the circuit boards 72 and at the inner extremity of the tray 70 there is a set of steel sockets 74 manufactured to very fine tolerances. The burn-in oven comprises a slide 76 on which the tray 70 slides for perfect registry of the sockets 74 with conductor pins 75 mounted on vertical rails 77 at the back of the burn-in oven as shown most clearly in Fig. 8(c). It has been found that this relatively simple arrangement provides for not only very speedy insertion and removal of a rack of boards for burn-in testing, but more importantly it improves the quality as plugs and sockets which would be liable to damage over time in the environment of a burnin oven are not required. Further, it would be immediately apparent, even to an inexperienced operator, if the rack has not been correctly inserted as the tray will quite apparently be in the wrong position on the rail 76. This feature has been found to provide a significant contribution to both the efficiency and quality of the production process. These steps are indicated by the numerals 19 and 20 in Fig. 1 and finally in step 21 final verification of the burned-in boards is recorded and the products are dispatched.

It has been found that the combination of steps of the overall production process of the invention provide for extremely reliable, efficient and good quality production.

The invention is not limited to the embodiments hereinbefore described, but may be varied in construction and detail.

Claims (10)

CLAINS

1. A production process for circuit boards, the process comprising : receiving raw materials; recording data relating to the raw materials, the data including a supplier identifier and a cross-referenced internally generated identifier; with reference to real-time data, a printing system printing a label containing raw material data, the label being colour-coded for immediate identification of the time of receipt of the raw materials; retrieving a batch of blank printed circuit boards; mounting the batch of blank circuit boards at the inlet stage of a screen-printing machine and applying epoxy to pre-defined portions of the board for wave-solder component locations; carrying out screen printing of the board by supporting the board on magnetic pillars, the location of the pillars being set by use of a guide plate having through-holes in which the pillars are initially inserted, the guide plate being pulled upwardly when the pillars are in position on the base plate of the screen printing machine; carrying out component placement operations by use of a rotating turret supporting driven applicator heads, the applicator heads being fed by a set of reel dispensers mounted on a sliding carriage, in which means are provided for monitoring alignment of the component dispensers above the carriage; heating the board by passing it through an oven for solder reflow; carrying out a visual inspection of the surface-mount soldered board; carrying out manual insertion of components on the board; wave-soldering non-surface mounted components; carrying out in-circuit testing of the soldered board and any subsequently required repair work; and carrying out burn-in testing.

2. A production process as claimed in claim 1, wherein the alignment monitoring means of the component placement machine comprises a light source and a sensor mounted in alignment above the dispenser heads, the sensors being connected to a machine control circuit for cutting power to the applicator heads on detection of mis-alignment.

3. A process as claimed in claims 1 or 2, wherein the component placement machine further comprises means for detecting dislocation of an applicator head on the turret of the control circuit for preventing further rotation of the turret on detection of displacement.

4. A process as claimed in claim 3 wherein the detecting means comprises a resilient probe mounted just below the circumferential path of the applicator heads, and an electrical limit switch at the base of the probe to detect movement thereof, the limit switch being connected to applicator head control circuits.

5. A production process as claimed in claim 4, wherein the probe is mounted adjacent to the component application position of the applicator heads.

6. A process as claimed in any preceding claim, wherein an individual inspection step involves recording on a medium data relating to nature and stage of faults, the recording medium being structured for immediate identification of faulty apparatus and faulty raw material such as a circuit board.

7. A production process as claimed in any preceding claim, wherein burn-in testing is carried out on a rack having conductors for transmission of test stimuli and for reception of output signals, the rack having a set of sockets with bores mounted in alignment with the direction of sliding of the rack in the burn-in oven, the burn-in oven having a set of rigid conductor probes mounted in alignment with the bores of the sockets on the rack for engagement with the rack sockets on sliding of the rack inwardly.

8. A production process as claimed in any preceding claim, wherein manual component insertion is carried out at a plurality of stations, each station having a bin support plate mounted for rotation about a central, vertical axis for change-over procedures.

9. A production process substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

10. A circuit board whenever produced by a process as claimed in any proceeding claim.