Method of producing a printed circuit board

A method of manufacturing a printed circuit board comprises providing an insulating substrate having opposed major sides, forming a through-hole between the two sides of the insulating substrate, forming a conductive land on both sides of the insulating substrate surrounding the ends of the through-hole, forming margining frames at the outer peripheries of the conductive lands, and packing conductive paste into the through-hole after the formation of the margining frames. The margining frames extend vertically beyond the height of the conductive lands and prevent the conductive paste from spreading outwardly beyond the outer peripheries of the conductive lands.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of producing a printed circuit 
board having through-holes. 
In a conventional method of forming a conducting path between the two sides 
of a printed circuit board having circuit patterns formed on one or both 
sides of an insulating substrate, as shown in FIG. 2, such work has been 
carried out by penetrating a through-hole 4 between lands 2 and 3 of the 
circuit patterns formed on the insulating substrate 1 and then packing 
conductive paste 5 into the through-hole 4 by silk-screen printing or the 
like. 
When forming the circuit patterns with a copper-film-cladded laminated 
board, the through-hole 4 is usually bored by punching or drilling prior 
to forming the circuit patterns, and then solder resist 6 is adhered after 
forming the circuit patterns by etching. 
When packing conductive paste 5 into the through-hole 4 in the manufacture 
of a conventional printed circuit board, it is also necessary to build up 
conductive paste 5 on the lands 2 and 3 to secure an electrical 
connection. 
However, while the paste 5 is usually packed by using a printing means such 
as silk-screen printing, this technique has a drawback in that the paste 
spreads or sticks on the outer periphery of the narrow lands 2 and 3. This 
has been a serious problem, because it often generates defects owing to 
bridge formation between adjoining lands and may also deteriorate the 
electrical insulation between lands, as high-density printed circuit 
patterns become practical. 
SUMMARY OF THE INVENTION 
An object of the present invention is to eliminate the above disadvantage 
of the conventional printed circuit board and to solve the above problems. 
Another object of the present invention is to provide a method of 
manufacturing a printed circuit board capable of packing conductive paste 
into a through-hole without deteriorating the electrical insulation 
between lands. 
According to the present invention, there is provided a method of 
manufacturing a printed circuit board which comprises providing an 
insulating substrate for the printed circuit board, forming a through-hole 
between the two sides of the insulating substrate, forming circuit 
patterns on one or both sides of the insulating substrate, forming 
margining frames on the outer peripheries of both ends of the 
through-hole, and packing conductive paste into the through-hole after the 
formation of the margining frames. 
According to the above construction of the printed circuit board, it is 
possible to prevent the conductive paste from oozing or adhering to 
undesirable portions of the circuit patterns and also to achieve required 
electrical insulation between the lands. 
These objects and other objects, features, aspects, and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DETAILED EXPLANATION OF THE PREFERRED EMBODIMENT 
FIG. 1 is an illustration showing a method of manufacturing a printed 
circuit board according to one embodiment of the present invention. 
Referring to FIG. 1, an insulating substrate 1 is made of a laminated plate 
cladded on both major surfaces or sides with copper film of approximately 
25 .mu.m in thickness. Prescribed circuit patterns (not shown) are formed 
on the two sides. 
Prior to forming the circuit patterns, a through-hole 4 is formed by 
boring, specifically punching or drilling, at the location where the two 
sides of the insulating substrate 1 are to be made conductive. 
After the circuit patterns are formed, solder resist 6 is adhered to both 
sides of the insulating substrate 1 by means of silk-screen printing, but 
is not adhered to lands 2 and 3 of the through-hole 4 or other electrical 
junction lands (not shown) such as lands for parts insertion. 
At the time of, or subsequent to, the adhering of the solder resist 6, 
annular margining frames 7 are each formed along the outer peripheries of 
the lands 2 and 3 by means of silk-screen printing or the like using the 
same solder resist ink or other insulating ink. 
Then, conductive paste 5 is packed into the through-hole 4 by means of 
silk-screen printing to provide an electrical connection between the lands 
2 and 3 through the conductive paste 5. 
The margining frames 7 serve to prevent outward oozing or sticking of paste 
5 beyond the outer peripheries of the lands 2 and 3, which could otherwise 
occur when packing conductive paste 5 into the through-hole 4. 
The above prevention can be most effectively accomplished by providing 
frames 7 whose layer thickness is 20 .mu.m or more greater than that of 
the copper film forming the lands 2 and 3. 
In addition, the frames 7 play a useful role in protecting the lands 2 and 
3 from undergoing exterior damage, such as scratches and dents in 
subsequent work processes.