High density multitrack magnetic head

A method for making a multitrack head is disclosed wherein, by use of two separate alignment structures, a head having a large number of perfectly aligned cores, with perfect track-to-track spacing, is provided. The described multitrack head, by virtue of the inventive alignment technique, acquires a plurality of lead-protecting channels, the leads which are associated with the head coils being carried through such channels.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates in general to multitrack magnetic heads and to their 
methods of manufacture, and in particular to a multitrack magnetic head of 
the type in which the discrete cores thereof--and magnetic shields between 
the cores--are contained within a bracket or similar structure. The method 
for making a multitrack head according to the invention allows for a high 
density of cores across the widthwise dimension of the head and, as a 
result of such inventive method, the resulting head structure embraces a 
number of novel, distinguishing, and desirable characteristics. 
(2) Description Relative to the Prior Art 
Before addressing the relevant prior art, it is considered appropriate to 
address first what is clearly not the art over which the present invention 
provides an improved manufacturing method and multitrack head structure: 
The invention has nothing to do with multitrack heads of the type in which 
head structures are formed by vapor deposition (or the like) with, or 
without, the use of photofabrication procedures. Rather, the art over 
which the invention provides improvement relates to relatively 
conventional multitrack magnetic heads in which discrete cores and 
magnetic shields are preformed and then housed within an enclosing and/or 
supporting bracket. 
Although there are many and varied multitrack heads, and manufacturing 
methods, over which the invention provides improvement, detailed reference 
is made to only one such prior art head and method, thereby to identify a 
particular problem solved by means of the invention. The prior art 
multitrack head in question is described in U.S. Pat. No. 3,807,042, 
issued Apr. 30, 1974 to Honeywell Inc. of Minneapolis, Minnesota. 
Referring therefore to U.S. Pat. No. '042, and in particular to FIGS. 8-11 
thereof, it is seen that a supporting block 14 is provided with deep slots 
15 and with shallow slots 16. Preformed core pieces 20, which are 
pre-wound with coils 24, are dropped into the shallow slots 16, and 
magnetic shields 18, 19 are dropped into the deep slots 15. Thereafter the 
head of U.S. Pat. No. '042 is completed by procedures which do not involve 
relevant prior art background for the invention; and thus, no further 
discussion is had as to those procedures. Careful note, however, should be 
made that in FIG. 11 of U.S. Pat. No. '042, the core pieces 20, as well as 
the magnetic shields 18, 19, respectively, extend completely into the 
bracket slots 16, 15. This sort of design represents the current state of 
the art. 
The Problem 
Whereas U.S. Pat. No. '042 discloses a multitrack head of just three tracks 
(the head widthwise dimension is not specified), consider the application 
of the procedure of U.S. Pat. No. '042 to the manufacture of a head having 
as many as 34 tracks per widthwise inch, wherein the track dimensions 
(core width) are (a narrow) ten mils, and wherein the shields have 
thicknesses of (as little as) 17 mils. Such being the case, this means 
that there are 
EQU 34.times.0.010"=0.34" plus 
EQU 33.times.0.017=0.561", 
for a total of 0.901 widthwise inches of block 14 of U.S. Pat. No. '042 
head that would have to be removed by slots to accommodate the core pieces 
and shields. This leaves just 0.099 widthwide inches out of which 68 
precision slot-defining wall members would have to be fabricated. Given 
that each wall member is, for example, identically sized, this would mean 
that each wall member would have to be about 0.099/68=0.00145 inches 
thick. At the current state of the art, it is absolutely impossible to cut 
34 ten mil precision slots and 33 seventeen mil precision slots in a one 
inch block, with each slot separated by a precise fin-like wall member of 
only 0.00145 inches thick. By means of the invention, however, a 
multitrack head having 34 tracks (0.010" track width) per widthwise inch, 
with shields between the tracks (shield thickness 0.017"), is indeed 
provided. 
Other prior art relevant to the invention may be found in the following: 
U.S. Pat. Nos. 3,593,414; 3,668,775; 3,761,641; 3,842,494; 3,843,968; 
3,851,375; and 4,084,199. 
SUMMARY OF THE INVENTION 
The concept of the invention is to split the prior art practice of 
providing a single grouping of slots in a single member into two separate 
groupings of slots . . . the first slot grouping being within a support or 
bracket for a head according to the invention, and the second grouping 
being in a precision jig that is separable from the head during its 
manufacture. The first slot grouping is disposed to accept and align the 
head shields; and the second slot grouping is disposed to accept and align 
the head cores.

A multitrack head according to the invention will be described with 
reference to its inventive method of manufacture: 
Referring to FIG. 1, a jig 10 is shown having a pair of alignment 
structures 12, 14. The alignment structure 12 is provided with a set of 
uniformly distributed slots 16 (i.e. a first slot grouping); and the 
alignment structure 14 is provided with uniformly distributed L-shaped 
recesses 18 which are as wide as, and are aligned with, the slots 16. In 
the fabrication of a 34 track (per widthwise inch) head according to the 
invention, the slot dimension W in FIG. 1 is equal to 0.015", and the 
space between the slots is 0.0185". 
Reference should now be had to the plan and side elevational views of FIG. 
2. Pre-wound core pieces 20 (thickness 0.0100") are set into the slots 16, 
the tips 21 of the core pieces extending into the L-shaped recesses 18 and 
abutting against the structure 14. Importantly, note should be made that 
leads 22, associated with coils 23 which are pre-wound on the core pieces 
20, are drawn along the edge 24 of the core pieces 20 toward the right in 
FIG. 2. 
Next (see FIG. 3), shield members 26 are set between each pair of adjacent 
core pieces 20. The shield members 26 are comprised of a pair of copper 
laminae 27a, b which sandwich a stack of high-mu laminae 28, the copper 
laminae 27a, b being provided with U-shaped cutouts 32 which reveal the 
high-mu laminae 29 and, in so doing, provide recesses 32a, b for 
accommodating the widthwise dimensions of the coils 23. The tips 28 of the 
shield members 26 are positioned so as to abut against the unrecessed 
corners 34 (FIG. 1) of the structure 14; and, importantly, the shields 26 
are wider (i.e. in the direction of the arrow Y) than the core pieces 20. 
A bracket assembly 38 (see FIG. 4a) having a set of slots 40 (i.e. a second 
slot grouping) which are 0.0185" wide--and which slots have the same pitch 
as the shield members 26 that are interleaved with the core pieces 20--is 
then placed over the assembly of FIG. 3, the upwardly extending shield 
members 26 fitting snugly into the slots 40 of the bracket assembly 38. 
The slots 40 of the bracket assembly 38 are pre-coated with epoxy or other 
cement and, as the shield members 26 are set into the slots 40, the 
bracket assembly tips 42 of its contour faces 44 are brought into abutting 
relationship with the corners 46 of the structure 14. See FIGS. 1 and 4b. 
Since the core pieces 20 are not as wide (in the direction Y; FIG. 3) as 
the shield members 26, channels 48 are formed between the core pieces 20 
and the bracket assembly 38 . . . and such channels 48 inherently result 
from a fabrication procedure that splits core piece alignment from shield 
member alignment. It is through the channels 48 that the coil leads 22 are 
brought for connection to using apparatus. 
Epoxy, or other cement, is then squirted into the channels 48 (and other 
voids) by means, for example, of a hypodermic needle, after which the 
whole assembly of FIG. 4b is set in an oven to cure the cement that bonds 
the shield members 26 to the bracket assembly 38, and the core pieces 20 
to the shield members 26. Such application of epoxy into the channels 48 
also serves to anchor the leads 22 so that they cannot be broken anywhere 
between the coils 23 and where they exit (50) the channels 48. 
With the parts 20, 26, 38 all bonded together, the structure of FIG. 4b is 
lifted free of the jig 10. (Thus, one of the two groupings of slots is 
effectively discarded--but used again--the parts which it had held being 
thereafter held in precise track-to-track positions by the cured epoxy.) A 
pole tip plate 53 (see FIG. 5) having high mu, wear resistant pole tip 
regions 54 of, for example, Alfesil, is then bonded to the core and shield 
assembly, with the pole tip regions 54 being in low reluctance contact 
with respective core pieces 20. Because the core pieces 20 had resided in 
jig slots 16, 18, whereas the shield members 26 had not, the faces F.sub.1 
and F.sub.2 (FIG. 4b) of the integral structure are serrated; and such 
serrations are removed by lapping (extremely flat) as noted by the two lap 
lines of FIG. 4b. Note again should be taken that despite the precise 
positioning of the core pieces 20, such core pieces do not reside in any 
bracket assembly (38) slots. 
(It will be appreciated that, for a variety of reasons, it is impossible to 
align shield members in the jig slots, and core pieces in bracket slots, 
and still produce an operative, efficient, and useful head structure.) 
Now, a multitrack magnetic head in accordance with the invention is 
finished/assembled according to practices well known in the art: 
(1) channels 58 are cut (FIG. 6) in the core and shield assembly, 
(2) gap spacing material is deposited on the faces 54.sub.f of the pole 
tips 54, and on the "front" face parts 20.sub.f of the core pieces 20, 
(3) a second core and shield assembly, just like the core and shield 
assembly of FIG. 6, is brought into abutting relationships with the first 
core and shield assembly, corresponding pole tips 54 and shield members 26 
of the two assemblies being in alignment (see FIGS. 7, 8), 
(4) with the core and shield assemblies held in close contact, glass, or 
other bonding material, is set into the channels 58, thereby to bond the 
core and shield assemblies together, 
(5) a contact panel 60 having a plurality of pins 62 is set (by suitable 
means) into a back cavity 64 that is formed when the two core and shield 
assemblies are bonded together, the contact panel 60 serving as an output 
connector for the coil leads 22 which are drawn through the channels 48 
(FIG. 4b). 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention. For example, whereas the above description has dwelled on the 
fabrication of a multitrack head having 34 ten mil tracks per widthwise 
inch, heads of differing numbers and densities or cores, and core widths, 
are within the contemplation of the invention.