GB2223835A

GB2223835A - Drying printed circuit boards

Info

Publication number: GB2223835A
Application number: GB8820324A
Authority: GB
Inventors: Wrenford John Thatcher; Allan Fawcus
Original assignee: Coates Brothers and Co Ltd
Current assignee: Coates Brothers and Co Ltd
Priority date: 1988-08-26
Filing date: 1988-08-26
Publication date: 1990-04-18
Also published as: GB8820324D0

Abstract

In a louvre dryer for drying printed circuit boards and having upward and downward conveying means for conveying printed circuit boards through various drying zones, there is provided, at a point between the upper parts of the upward and downward conveyors, guide means (6) for guiding a printed circuit board being transferred from the upward to the downward conveyor, the guide means being provided supported on pivotally mounted support means so that the distance between the guides may be varied to accommodate varying sizes of printed circuit boards, the louvre dryer also being provided with means (8) for controlling the distance between the guide means. <IMAGE>

Description

Drying APparatus This invention is concerned with improvements in and relating to drying apparatus. More particularly, the invention is concerned with apparatus for drying printed circuit boards to which have been applied a layer of a driable coating material, especially a layer of a solder resist which has been applied by a curtain-coating process.

A known form of drying apparatus for drying printed circuit boards, the so called "louvre dryer, basically comprises a housing defining one or more drying zones (to which hot or cool air is supplied to assist in drying) and means for moving the printed circuit boards through the drying zones, basically by firstly raising them vertically by appropriate conveying means, transferring them from the upward conveying means to downward conveying means and, after drying, removing them from the downward conveying means. The conveying means employed to raise and lower the printed circuit boards are of the so-called "louvre" type. Thus each conveying means comprises a pair of endless belts, mounted on suitable bearing and driving means, with one face of each belt generally parallel to a face of the other and with both such faces generally vertical.Each belt is provided with a plurality of slats or louvres arranged with their major axes generally horizontal and their minor axes at an angle to the horizontal. The slats on each belt are so arranged that the slats on one belt are at the same vertical level as those on the other belt and also are arranged so that pairs of facing slats on each belt have their facing edges lowermost, i.e. they form between them part of a V-shaped arrangement, for supporting a printed circuit board. As will be appreciated, by having these facing slats angled in this way it is possible for the conveying means to carry printed circuit boards of varying sizes without necessitating alteration of the spacing between the belts.

In operation the belts, and hence the slats thereon, are moved stepwise and thus, for any particular printed circuit board, the series of steps involved comprises firstly a feeding step onto the upward conveyor, stepwise movement up that conveyor until the board reaches an upper part of the conveyor, transfer across from the upward conveyor to the downward conveyor, stepwise movement down the downward conveyor and, finally, removal from the downward conveyor.

It has been found in practice that some mis-orientation of the printed circuit boards may occur during the step of transferring from the upward to the downward conveyor and such mis-orientation can give rise to problems and possible damage to the boards.

In accordance with the present invention, a louvre-type dryer of the type described is provided, at a point between the upper parts of the upward and downward conveyors, with guide means for guiding a printed circuit board being transferred from the upward to the downward conveyor; said guide means being supported on pivotally mounted support means so that the distance between the guides may be varied to accommodate varying sizes of printed circuit boards; and with means for controlling the distance between the guide means.

In a simple embodiment of the invention, the distance between the guide means may be controlled by the action of the printed circuit board itself passing between the guide means and urging them against the resilient action of a spring or the like connected to the pivotally mounted support means. Alternatively, the distance between the guide means may be controlled by air-operated pistons having pressure limiting means to avoid damage of the printed circuit boards by the guide means.

In order that the invention may be well understood reference will now be made to the accompying schematic drawings in which: Figure 1 is a side view illustrating the operation of a louvre dryer; Figure 2 is a vertical section showing the operation of louvre-type conveying means; Figure 3 is a plan view of one embodiment of guide arrangement in accordance with the invention; Figure 4 is a an elevation of the guide means shown in Figure 3; and Figure 5 is an elevation of another form of guide means in accordance with the invention.

As shown in Figure 1, in a louvre-type dryer the boards 1 are fed from a horizontal conveyor 2 into an upwardly moving stack supported by a louvre-type conveyor; transferred from that stack to a downwardly moving stack supported by another louvre-type conveyor and finally transferred back to conveyor 2.

As shown in Figure 2, louvre-type conveying means basically comprises a pair of endless belts, 3 and 3 mounted upon appropriate drive and support rollers 4 and provided with louvres or slats 5, facing pairs of which can support a printed circuit board 1, as shown. As will be appreciated, the arrangement shown in Figure 2 may be adapted for upward or downward movement of the printed circuit board 1.

In accordance with the invention, printed circuit boards, when being passed from an upwardly moving stack to a downwardly moving stack, (by means of a push rod or like means, not shown) are guided by guide means. In the embodiment of guide means shown in Figures 3 and 4 the guide means 6 are supported by pivotally mounted shafts 7 the rotation of which (and hence of the guide means) is controlled by air operated pistons 8.

In the embodiment shown in Figure 5 of the drawings, a pair of guides 6 are each mounted on support shafts 7, mounted for rotation in a vertical plane about pivot points 9. Movement of the shafts 7, and hence guides 6, is controlled by air operated pistons 8. If desired, an and appropriate linkage (not shown) may be introduced between shafts 7 to ensure that guides 6 are each at the same distance from the centre line of the device. In operation of the device shown in Figure 5, it is convenient to bring guides 6 into contact with a printed circuit board to be guided only at the time of transfer thereof from the upward to the downward stack and this may be achieved by appropriate control of the supply of air to pistons 8.Whilst not shown in Figure 5, it has been found convenient to arrange the board engaging parts of the guides 6 so that they engage with two boards in the upward moving stack (or downward moving stack) at the same time, namely the uppermost two boards in the stack. In this arrangement it is particularly convenient if the guide is so arranged that whilst the penultimate board is relatively tightly gripped, the uppermost (ultimate) board is slightly less tightly gripped to allow for easy transfer thereof from the upward to the downward stack. In other words, the portions of the guide adapted to guide the topmost board should be slightly further apart than the parts of the guides intended to cooperate with the board immediately below it. With this arrangement it is particularly desirable that the guides be brought out of engagement with the printed circuit boards during the intermittent periods of vertical movement of the stacks.

Claims

1.. A louvre-type dryer of the type described provided1 at a point between the upper part of the upward and downward conveyors, with guide means for guiding a printed circuit board being transferred from the upward to the downward conveyor, said guide means being supported on pivotally mounted support means so that the distance between the guides may be varied to accomodate varying sizes of print circuit boards; and with means. for controlling the distance between the guide means.

2. A dryer as claimed in claim 1 in which the control means comprises resilient springs or the like connected to the pivotally mounted support means and urging the guide means together.

3. A dryer as claimed in claim 1 in which the control means comprises a pair of air-operated pistons connected to the pivotally mounted support means and having pressure-limiting menus to avoid damage of the printed circuit boards by the guide means.

4. A dryer as claimed in claim 1 substantially as hereinbefore described with reference to the accompanying drawings.