Pallet for drying ceramic cards

A pallet for use in drying ceramic cards that have product sites thereon, including a body having a plurality of openings therein defined by a series of highways, whereby the openings have the general shape of the product sites; at least one skirt extending perpendicularly from the body contains an open slot or recess located adjacent the front of the body; at least one skirt extending perpendicularly from the body contains an open, rearward facing, elongated slot adjacent the rear end of the body; a series of clusters of holes are provided along the perimeter of the body.

BACKGROUND OF THE INVENTION 
1. Technical Field 
This invention relates to the manufacture of multilayer co-fired ceramic 
substrates for packaging integrated circuit chips, and more particularly 
to a unique pallet for drying green ceramic cards used in making such 
substrates. 
2. Description of the Prior Art 
Techniques for manufacturing multilayer ceramic cards that are used for the 
above substrates in the electronic industry are well known in the art. 
U.S. Pat. No. 4,539,058 to Burgess et al., and U.S. Pat. No. 4,497,677 to 
Sanada et al. are two references that discuss such techniques. 
In general, multilayer ceramic cards are made from green sheets of ceramic 
material. (The term "green" refers to unfired ceramic bodies.) Each green 
sheet contains a plurality of spaced apart product sites. The sheets are 
made by forming a slip from a mixture of ceramic powder, organic binder, 
and solvent. The slip can be cast onto a suitable sheet material and 
dried. The green sheets, after blanking, are then stacked, processed and 
laminated. The product sites are cut from or punched out of the laminated 
stack and sintered. 
In accordance with prior art methods, the green sheets are transferred 
through dryers by continuous type belts. Such techniques require manual 
loading and unloading. Since the green sheets are fragile and easily 
broken and torn, manual handling results in high production losses and 
costs. In addition, contamination is transferred from the belt to the 
green sheet. Attempts at automatic loading and unloading of these belts 
have produced smears and product contamination due to the sliding of the 
part on the moving belt during part removal. 
SUMMARY OF THE INVENTION 
To eliminate this problem, the present invention employs a pallet that is 
supported by transverse rods, the pallet supporting the part fully. 
Movement of the pallet and card through the dryer is indexed so that only 
during the stopped portion of the cycle is the card either placed onto or 
removed from the pallet. This totally eliminates any sliding action at the 
part/pallet interface. 
The stopped position of the pallet either at the entry or exit end of the 
furnace (dryer) can be determined by electrical sensors. Such sensors 
provide positional accuracy and allows ease of part placement and removal. 
It is therefore an object of this invention to provide a pallet for use in 
loading and unloading green ceramic sheets. 
It is another object of the present invention to provide an easily 
assembled and disassembled pallet. 
It is still another object of the present invention to provide a pallet 
which will facilitate a mechanism for chordal action when directed around 
sprockets. 
It is still another object of the present invention to provide an easily 
made and inexpensive pallet adaptable to varying configurations for 
various product types. 
These and other objectives are met by a unique pallet for receiving and 
unloading green ceramic cards. The pallet is mounted on a front rod and a 
rear rod by means of a rearward facing elongated slot provided at the rear 
end of the pallet, and a recess at the front end of the pallet extending 
in a direction generally perpendicular to the plane of the pallet. The 
elongated rear slot and the front recess allow for quick engagement and 
disengagement of the pallet from the rods. In addition, the elongated rear 
slot and the front recess facilitate the movement of the pallet around 
sprockets which are used to return empty pallets to a location for 
receiving new green ceramic cards.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In forming multilayer ceramic cards in accordance with the present 
invention, conventional methods, as described above, can be used to form a 
green sheet. Once the slip is cast, it is allowed to partially dry. The 
slip is then cut into ceramic cards 2, one of which is shown in plan view 
in FIG. 1. Each ceramic card 2 includes a plurality of product sites 4, 
which are ultimately punched therefrom, laminated, stacked and cured to 
form the final product. The product sites 4 can have various 
configurations. FIG. 1 illustrates a ceramic card 2 having a configuration 
of nine square product sites 4. 
After the partially dried slip is cut into cards 2, the cards are screen 
printed with an electrically conductive paste. Referring now to FIG. 2, 
the cards are then transferred to pallets 6 (of the present invention) and 
carried through a suitable furnace (not shown) for drying. FIG. 2 
illustrates a preferred embodiment of pallet 6, which comprises a planar 
rigid main body portion 8 having a plurality of openings 10 therein, which 
are defined by a series of connecting highways 12. The openings 10 can be 
of various configurations, and are identical to the configuration of the 
product sites on the ceramic cards which are ultimately dried thereon The 
pallet 6 illustrated in FIG. 2 includes nine square openings 10, though 
not limited thereto, which are similar to and coincide with the nine 
product sites 4 on the ceramic card 2 illustrated in FIG. 1. When the 
ceramic card 2 is transferred to the pallet 6, the nine product sites 4 
are aligned with and lie over the nine openings 10, thereby preventing the 
product sites 4 on the ceramic card 2 from contacting the surfaces of body 
8 of the pallet 6. This reduces the possibility of contaminating the 
product sites 4. Since the design of the end products vary and thus the 
shape of the product sites 4 vary, in accordance with other embodiments of 
the present invention, the pallet 6 can have different interior 
configurations corresponding to other end product designs. 
In a preferred embodiment of the invention, pallet 6 further includes two 
side wall portions or skirts 14 that extend generally perpendicularly from 
opposite sides of the main body 8. As can best be seen in FIG. 3, each 
skirt 14 is provided with an open, rearward facing, elongated slot 16 
adjacent to the rear of the pallet, which extends forward from the rear 
end of said skirt in a direction generally parallel to the plane of the 
main body 8. Each skirt 14 further includes an open recess 18 near the 
front of the pallet, which extends from the edge of and into the skirt in 
a direction generally perpendicular to the plane of main body 8. 
In an alternative embodiment of the present invention (not illustrated), 
pallet 6 can include four skirts, with two extending generally 
perpendicular from opposite sides of the front of main body 8, and two 
extending generally perpendicularly from opposite sides of the rear of 
main body 8. In accordance with this embodiment, each of the forward 
skirts incudes an open recess 18, and each of the rearward skirts includes 
an open elongated slot 16. 
As illustrated further in FIG. 2, and in accordance with the present 
invention, the pallet is attached to and supported by two rods 20 and 22 
suitably connected to a conveying means (FIG. 6). Rod 22 is considered a 
front rod and rod 20 a rear rod. The rear rod 20 is first inserted into 
the elongated slot 16. As shown in FIG. 4, the front rod 22 includes an 
indentation 34. The recess 18 is then placed over the indentation 34 on 
front rod 22, and a clip 24 is inserted through the rod on each side of 
the pallet to laterally retain the pallet. This unique attachment 
mechanism utilizing the recesses and slots enable an operator to quickly 
change the pallet when a ceramic card having a different configuration is 
to be made. 
In accordance with a preferred embodiment of the invention, an array of 
pallets is used to form an automatic loading and unloading operation for 
transferring ceramic cards through a furnace. Such an array is illustrated 
in FIG. 5. In particular, a series of pallets 6 are connected by and 
supported on a series of front and rear rods 22 and 20 suitably connected 
to two parallel roller chains 36 (only schematically depicted in FIGS. 5 
and 6). Roller chains are power driven chains comprised of links similar 
to those found in bicycle chains. The ends of the rods are an integral 
part of the links such that the chains carry the rods and the pallets 
through the drying process. As illustrated by arrow 26, the rods carry the 
pallets in a direction perpendicular to the rod axes. Each pallet 6 is 
secured to the rods in the manner described above. 
When the ceramic card 2 is formed, it is placed on a pallet 6 and 
transferred through a furnace. After leaving the furnace, the card is 
preferably vacuum lifted from the pallet 6 only when the pallet is stopped 
on the indexing cycle, and taken to other stations for further processing. 
As illustrated in FIG. 6, empty pallets are returned to a location for 
receiving new green ceramic cards by use of roller chains 36 and sprockets 
28. Each pallet 6 is carried by the chains and rods through the process 
and returned to the beginning of the process where a new ceramic card 2 is 
transferred to a pallet. At least two sprockets are included in the loop 
to change the direction in which the pallets travel. 
The elongated rearward slot 16 provides means to reduce the distance 
between the front rod 22 and the rear rod 20 automatically to facilitate 
the circular movement around sprocket 28. As the pallet 6 travels around 
the sprocket, the rods enter a sprocket mode, i.e. the pallet forms chord 
on the circle of the sprocket. The distance, therefore, between the rear 
rod 20 and the front rod 22 decreases on the sprocket. The rods securing 
pallets 6c and 6d in FIG. 6 are shown in the sprocket mode. In addition, 
rear rod 20a in FIG. 3 is shown in its sprocket mode position. When the 
pallet 6 leaves the sprocket 28, the distance between the two rods 
increases and the rods return to a straight line mode in which the 
distance between them is not affected by circular travel. The rods 
securing pallets 6a, 6b, 6e and 6f in FIG. 6 are shown in straight line 
modes. Similarly, the rear rod 20b in FIG. 3 is shown in the straight line 
mode. 
As can be seen in FIGS. 2 and 3, the wall portions or skirts 14 may also 
include perforations 30 which lighten the pallet 6, and reduce its overall 
thermal mass. This is desirable for two reasons. First, pallet 6 is more 
easily translated, removed and inserted if it is lighter. Second, when the 
pallets enter the furnace they are at room temperature. As a result of the 
temperature differential between the pallets and the furnace, the pallets 
tend to cool the furnace. Since the perforations reduce the thermal mass, 
there is less of a tendency to remove heat from the furnace, and greater 
efficiency of energy is achieved. Additionally, as the pallets/parts exit 
the furnace, they can be cooled more easily due to the lower thermal mass 
of each pallet. Referring to FIG. 2, the body of pallet 6 is shown 
provided with a series of clusters of holes 32. Such holes 32 are 
preferably on the order of 1/16th inch in diameter, and are located along 
the perimeter of the body 8. The purpose of such holes 32 is to prevent 
the vacuum that lifts the card from the pallet from imposing a force upon 
the pallet. 
While the invention has been described in terms of preferred embodiments, 
the claims appended hereto are intended to encompass all embodiments which 
fall within the spirit of the invention.