AU500570B2 - Method for cleaning holes in resin-containing materials - Google Patents

Description

FORM 4 COIYION14EAT.TH OF AUSTRALIA Patents Act 1952-69

CONVMENTION APPLICATION FOR A PAT 4 i. We, Kolimorgen Ccrporation,

of 60 Washington Street, Hartfo'd, Connecticut, United States of America, hereby apply for the grant of a Patent for an invention entitled

METHOD FOR CL-EANING HOLES IN RESIN-CONTAINING MATERIALS which is described in the accompanying complete specification. This application is a Convention Application and is based on the application numbered 521,890

for a patent or similar protection made in the United States rof America

c~ on 7 November 1974.

M, Our address for serviice i&L1CATV N ACQEPTeDA eq C C C

CC Care: Spruson Ferguson C Cb. Patent Attorneys Esso House, 127 Kent Street Sydnpy, New South Wales, Australia.

Dated this ZiA 4 day of 4f j~975~ *4* C C

Mall Offloor The Comnu Seal of Kollmorjgen Corporation war hereto a2fxJin Signature 4 z N '1pcant P. Bur# %'Ajce President ;rob

COMMONWEALTH OF AUSTR{ALIA

DECLARA~TION IN SUPPORT OF A CONVENTION APPLICATION FOR A PATENT OR PAIENT OF ADDITION In support of the Convention Application made for a patent for an invention entitled -*METHOD FOR CLEANING HOLES IN RESIN-CONTAINING MATERIALS!$

IRobert P. Burr

olC R.D. 3, Lloyd Lane, Lloyd Harbor, co Huntington, New York, United States of America

do solemnly and sincexely declare as follows:-

1. 1 am authorised by Kolimorgen Corporation the

*.applicant for the patent to make this decle-ration on its behalf.

The basic application as defined by Section 141

of the Act was ,made in the United States of America

*on the 7th day of November 1974 by Joseph Polichette, Edward J. Leech, John G. Branigan and Joseph P. Hammond.

3. Joseph Polichette, 9 Hitchcock Lai, South Farmingdale, Edward J. Leech, Center Island, Oyster Bay, John G. Braaigan, 10 'Hazel Drive, Smithtown, Joseph Hammond, 67-IOB 190 Lane, Fresh Meadows, all of the State of *New York, the United States ofAmrc-. AUSTRALIAN

XK/are the actual iriventor(s) of the inv- nti~hi".anri4 he facts upon which the a~-'licant is entitled to make the application are as follow,-s: The said applicant is the assignee of the actuial inventor(s).

4. The basic applicatiou refEerred to in paragrapb. 2 of this Declaration was the first application made in a Convention count'ry in respect of the invention dte subject of tk.he application.

Declared at G-k6L i ,tth is Z JN4 d ay o f 1E~l7

Signature of Declarant Robert P. Burr, Vic' President, g(11) AU-B 86328/75

(12) PATENT SPECIFICATION ABRIDGEMENT (19) AU

(21) 86328/75 500,570 (22) 5.11.75 (23) 5.11.75 (24) 7.11.-4 (31) 521890 (32) 7.11.74 (33) US 12.5,77 (44) 24.5.79 2 (51 B05D 3/10 B08B 9/02 C08J 7/12 H05K 3/00 (54) METHOD FOR CLEANING HOLES IN RESIN-CONTAINING MATERIALS (71) KOLLMORGEN CORP. (72) POLICHETTE, J. LEECH, BRANIGAN, J.G. HAMMOND, J.P. (74) SF (56) 61759/73 480398 07.6 47.7-57 47.7-77 52.8 11553/66 70,8 75.8 8622/66 410403 75,8 73.1 (57) CLAIM I. In a process for the manufactur-e of articles comprising at least one hole formed in resin-cc:itaining materials, the improvement in cleaning smears of resin froir the barrel of said hole consisting cf contacting said hole barrel with an alkaline permanganate solution having a pH of at least 13 and an elevated temperature above room temperature for a period ranging from twenty to fifty minutes.

18/4

COMMONWEAP.TH OF AUSTRALIA Form 3 PATENTS ACT 195269

OCOMPLETE SPECIFICATION (ORIGINAL) FOR OFFICE USE:

0 Class int. Class Application Number Lodged

rpmplet,- Specification Lodged Accepted Published

'or Ity

:Ve at ed Art

P~ fh t -k r

XOLLK0RGN CORPORAT ION jAome of Applicant

*Address of Applicant 60 Wasbington Street, Hartford, Connecticut, 9 United States of America~

ActualIlnventors. JOSEPHi tOLICHETE, ED10ARD J LEECH, jOHW BpP.NI(~1N and JOSEPH P. HA.MMOND 66.

Address for Service Spruson Ferguson, Patent Attorneys,__Esso House, 127 K~ent Street, Sydt, ty, !New South Wales, 2000 Australia. ~-5NOV iZ

Complete Specification for the invention intitled: "METHOD FOR CLEANING HOLES IN RES IN-CONTAINING MATERIALS"

The following statenment is a full description of this invention, includjing the best rnethod of performing it known to suus r V F A? ramut" f -LXIsclosure

A method c the use of alkaline permanganate

treating solutions to remove resin timea the interior

%ialls of holes formed in resin-containing materials.

Hole-forming operations in resin-containing materials CO C often result in the smearing of the resin over the interior walls or barrels of the holes. This cesin smear is primarily attributable to the generation or utilization of temperatures exceeding the melting point of a resinous component of the material during hole-forming operations.

When holes are drilled in epoxy-impregnated fiber-

S. glase larinate materials, for example, the friction of the drill hit against the material raises the temperature of the bit. Numerically controlled drilling machines are in common use today, and they are capable of a very rapid drilling se- quence, up to 200 holes per minute. Under these conditions, drill bit temperatures of 500 to 600°F occur, and such temper- S*,

atures exceed the melting temperature of epoxy resins. The

drill tt thus picks up melted epoxy resin on its course through 1 20 the material being drilled, and upon withdrawal of the bit this melted epoxy accretion is smeared in the barrel of the

hole. While the resin smeared on the hole walls may be ignored in some applications, it is at times imperative that it be removed. Consider, for example, a hole that has been formed in a resin-containing material which includes a plural- ity of parallel planar conductors, with the hole perpendicular to, and communicating with, two or more of the parallel con- ductors. If it is desired to metallize the hole walls in or-

Q der to form a conductive path between two or more of the 'a 2

t-

V,,

conductors, the resin smear must ,1 removed from the edges of the hole through the conductors if conductive contact between

the metallized hole wall and the conductors is to be achieved.

to Plated throuch-holes as described above are useful

oO as electrical connectors between printed circuits having con-

ductors on both sides or between two or more of the various

.e planes in multilayer boards. The electrical and mechanical 00 integrity required for this function can only be attained by

insuring complete removal of resinous materials from the en-

10 tire inner circumference of the portion of the conducting lay-

*er exposed by the hole. Another instance where resin smear removal is essen- S

tial is in the formation of wire assemblies according to U.S.

o Patent No. 3,646,572 to Burr, the disclosure of which is here-

by incorporated by reference. This is also the preferred

application of the instant invention. Such wire assemblies may

include, for example, networks of fine insulated wires imbedded

in a resinous surface of a substrate. Interconnection between

these wires and other conductors may be established by, for

20 example, drilling a hole perpendicular to the wire planes of such a diameter and location that it intersects the wire, met-

allizing the barrel of the hole and the intersected tip of the

wire, and soldering a connection to the metallized hole. If

resin smears are not thoroughly removed from the hole wall and

the wire tip, poor or no electrical contact between the metal-

lized hole wall and the wire tip may result. Moreover, even

if acceptable electrical contact should be initially achieved

when an unclean hole is metallized, this contact may be lost in a later soldering operation due to expansion of the resin smear rupturing the physical contact between the metal hole

wall and the intersected wire.

Numerous methods are known for removing the resin smear. One approach is a mechanical one and involves the channeling of a dry or wet stream of abrasive particles through such holes. A similar method is the use of hydraulic pressure to force a thick slurry of abrasive material through the holes. 00 Mechanical methods generally are relatively slow and difficult C9 C"D to control. Moreover, complete smear removal is rarely assured o since good reproducibility with respect to all of the holes in a given circuit board is difficult to achieve. S

LO The more popular and reliable known methods of 6* smear removal include the use of chemicals that attack the 0 smeared resinous coating. .9

S S *SS* Concentrated sulfuric acid down to abo ut 90 percent concentration has been successfully used. Smeared resin,

which is usually less than about 0.001 inch thick, can be re- moved with about one minute's treatment with such an agent. S Unfortunately, the high sulfuric acid concentration required

5 for effective smear removal also demands extraordinary precau- tions by operators, which generally result in a slow, uneconom- S

20 icaL overall process. S S 5* 4

Concentrated chromic acid is also a known useful smear-removal agent. It is slower-acting than sulfuric acid, requiring from five to fifteen minutes for equivalent smear removal, and also requires operator caution. Special tank linings and immersion racks are also required. Increasingly

strict water quality regulations and the difficulty of dispos- ing of chromic metal residuals in an ecologically satisfactory manner also weigh against this method of smear removal. Various ratios and combinations of sulfuric and fluorine-containing acids are also useful, but these are extremely toxic, requiring specially designed equipment, fume exhaust, and so forth.

Permanganate has been suggested as a useful smear-

removal agent, as it does not require special equipment or

0 extraordinary safety precautions 'or operators and presents 04 C no ecological hazard in wast disposal. <c e It is an object of this invention to present an

effective smear-removal process utilizing permanganate.

It has been found that an effective permanganate 10 hole-cleaning process is highly time-dependent once the vari-

ables of temperature and agent concentration have baen optim-

ized.

SS S 9 An effective industrial process for the removal of

Sresin smears from hole walls includes treatment for about

twenty to about fifty minutes with an alkaline permanganate

solution, preferably at a temperature of from about 40 C to about

Figures 1 to 3 illustrate the resin-removal rate of

solutions according to the invention for various concentrations

S 20 of permanganate at 40°C. The effects of solutions at 60°C are

depicted in Figures 4 to 6 f-r various concentrations, and

Figure 7 illustrates resin-removal rates according to a known

treatment with chromic acid.

Surprisingly, we have found that at constant perman-

ganate concentration and constant temperature, the rate of

smear removal is nonlinear, When a resinous sample is first

immersed in a treatment bath according to the invention, the

amount of material removed is directly proportional to the

treatment time for an initial period. It is believed that

there then occurs, through phenomena that are not understood, a second period during which the resinous material being treated undergoes a weight gain, which is followed by still another period of weight loss. This is especially surprising in view of the fact that similar tests with a chromic acid 00 solution revealed a linear increase of smear removal with respect to time. One possible explanation for the observed 00 cycle of weight loss-weight gain-weight loss is that after an initial weight loss a crust accumulates on the initially- attacked area. Such a crust could be formed, for example, 10 of oxidation by-products resulting from the permanganate et- ching, The second period of weight loss could follow u slough- ing off of such a crust, resulting in the exposure of a fresh su-face to oxidative attack by the alkaline permanganate. We have also found that processing circuit boards to removc resin smears for times running significantly into the second weight-loss period results in inferior printed circuits and wire assembly circuit boards. It is believed that the further etching occurring in I the second weight-loss period results in a conversion of the

20 substrate from resin-rich to, for example, glass-rich where the substrate is a resin/fiberglass laminate. It is further believed that the inferior results are attributable to metal- lization occurring in glass-rich voids in overly-etched hole walls, and that upon through-hole plating, there is a wicking action along the glass strands that results in poor or unaccep- table plated through-holes. Operationally, we have noted that hole-cleaning treatment times extending significantly into the second weight- loss period have resulted in wire assembly circuit boards ex- hibiting blow-holes and gas-caps during soldering where the metallized surface was autocatalytic to electroless metal de- position, and we have noted a breakdown in insulation resis- tance in such boards where the metallized surface was seeded ia to render it catalytic to electroless metal deposition. 00 Practice of the processes of this invention also requires a balancing of the solution components to best effect desired relative etching where more than one resinous material i00 is to be etched. For example, if holes in wire assemblies are to be etched, the insulated wire may have a polyimide coat-

4. 4* ing, the base laminate may be G-10, an epoxy-glass laminate, 4

and there may be a third resinous component in the form of a

*4C resinous adhesive on the surface of the bape. Resin smeared 4 9 in holes formed in such wire assemblies will likely be a mix-

ture of all three resin components. Moreover, it would be de-

a. sirable to etch back the polyimide insulation on the wire tip

at the same time the r-sin smear is cleaned from the hole

barrel in order to insure a firm connection between the wire

tip and the metallized hole wall and avoid a simple butt joint

Su following through-hole plating. The preferred processes of

4 this invention are directed to the wire assembly herein des-

cribed. Those skilled in the art may easily adapt the perman-

ganate etchants disclosed to suit particular applications and

resin-containing compounds.

It is desirable to effect smear removal in pernan-

ganate solutions over periods of time not significantly exten-

ding into the second weight-loss portion of the etch cycle. BC

The preferred treatment times for compositions, concentrations

and temperatures disclosed are within the range of from ebet-

twenty to ahet fifty minutes, with the most preferred treat-

ment periods ranging from abou thirty to aet forty-five minutes. The smear removal rate increasea with increasing per- manganate concentration. We have found the optimum perman- ganate concentration to be that corresponding to about 60 grams/ liter potassium permanganate. CID We also found the smear removal rate to be directly proportional to the temperature of the treating solution, with

00 elev-ed temperatures from abee 400 C to ebeat 60°C yieldinq

satisfactory results. Our preferred temperature is about 600 C.

Operating smear-removal baths according to the present invent- 0 0 ion at temperatures significantly less than about 40 C gener-

S 0 ally results in an unsatisfactorily slow smear-removal rate *5 and leads to difficulty in maintaining sufficient amounts of

permanganate in solution. Temperatures significantly above *0

result in increased permanganate demand in order to main-

tain the bath composition without yielding any apparent ad-

vantages, the overall process becomes less efficient in

terms of permanganate consumption. S We further prefer the pH of the solution to be at

least abcw 13, with the preferred pH being aheem 13.4 to abeet

13.5. Sodium hydroxide is the preferred pH adjuster. All 0 If a pH of pH values herein are measured at about 25 C.

significantly less than 13 is used, the etch ratio among the

different resin components is changed and is less desirable in

the herein described wire assembly applications.

Improved smear removal is obtained by the addition

of a small amount of wetting agent, such as the fluorinated

hydrocarbon wetting agents. The most preferred species of

the latter wetting agents is FC-128, sold u der theeade-ase Fluorad by the Min\~ota Mining and Manufacturing Company, St. h~ 6 C1 8

~I

Paul, Minnesota. The foll~owing examples illustrate processes according t~j the inventio., with the solutions of Examples .1tbrough 7 resulting in pH 'values above 13. I' Example 1 An aqueous jeolution of alkaline permangar&te was formed of 20 grams/liter potassium perzaanganate, 37.5 grams' liter sodium hydroxide, and the remainder water. The solution

4~ was brought to 40 0 C and maintained constant at that temperature. e 10 Three-inch squares of epoxy-impregnated material (Norplex S. S S S S so S one-sixteenth inch thick and weighing about 17 grams were S 5 immersed in the heated solutii~n for varying lan-gths of time, .4 .9 S 5595 S resulting ia the percent weight losses indicated below as a S.

S S S function of time; Table I Sample No. Treatment Time Percent Weight Loss (minutes) (X 104) 0S

1 10 1.3 2 20 2.8 3 30 3.8 a

4 40 1.8 50 1.2 6 60

These data are plotted ILn Figure 1 and yield the smoothed curve illustrated. Example 2 T

The procedure of Example 1 was followed, excepting that the solution contained 40 grams/liter potassium, permangan- ate, and the following results obtained.

7/

Table II Sample No. Treatment Time Percent Weight Loss

7 10 2.6 1I a 20 4.7 9 30 3.9 40 3.1 11 50 4.8

a. 12 60 1.6 a a a 10 The above data are plotted in Figure 2 and yield a. a 0. a

a the depicted smoothed curve. a. *a a. a a a Example 3 a. a S a. S The procedure of Example 1 was followed, excepting a. a a a that the solution contained 60 grams/liter potassium perman- *9

ganate, with the following results:

Tablae II a. a a a a a. Sample No. Treatment Time Percent Weicht Loss a. a a.. A (minutes) (X 0.90.. a 13 10 2.9 a :~o 1.4 20 3.2 a *a a a 15 30 R*S S

16 40 4.3

17 50 4.1

18 60 4.6 The data are plottLed in Figure 3 and yield the smoothed curve illustrated. Example 4 The procedure of Example 1 was followed, excepting that the solution was maintained at a constant temperature of

60c aqd the results of Table IV obtained:

Table I V Sample No. Treatment Time Percent Weight 'joss

fminutes) (x 10 4) 19 10 3.2 20 4,4 21. 30 5.4

22 40 4.7

23 50 3.2

24 60 ~0 B B B 10 These data are plotted in Figure 4 and yield the in- ta B B b *B B dioated smoothed curve. B. OB B. 0 0 Example B. .0 B -B B. B P The procedure of Example 2 was followed, enrcept B* iB B B that the solution temperatur~e was according to Example 4: B.

Table V Sample No. Treatment Time Percent Weight Loss BE B B B (minutes) (X 10'4 B. 0 0*h a 25 10 4.8

a 26 20 6.3 B *BB* BO B 27 30 6.7 0

a p. B 2840 B

29 50 4.2 60

These results are illustrated in Figure ExamTple 6

The procedure of Example 3 was followed, except that

the solution teniparatare was according to Example 4:

il

Sample No. Treatment Time Percent Weight Loss

31. 10 5.7 32 20 6.6 0- 33 30 7.3

34 40 5.9

0035 50 7.6

te36 60 Figure 6 illustratee the plot of these data and .th smoothed curVt fitting the. ExS.e 7*

SA control bath utilizing a known hole-c.Leaning form-

::ulation of e4,hromic acid was prepared by adding 915 grams/liter cr0 3 to water. The procedure of the preceding examples was followed, with the bath being at room temperature (about 200 C). Table VII *Samuple No.. Treatment Time Percent Weight Loss

(minutes) (x iQ0 37 1.0 2.9 38 20 4.2 39 30 5.7 40 B.7 41 50 11 These data are plotted in Figure 7 and yield the straight line indicated. As demonstrated in the examples below, marked in- creases in smear-iemovai3 rates may be obtained through the addition of a wetting agent to the preferred treating solution.

The. preferred wetting agents are characterized by a stable

'i 117,V

fluorocarbon taiA*l and a solubiliving group, ~.The solubiliz- ing group can be organic or inorganilc, anionic, cationlic, nonionic, amphoteric and water soluble. The wetting agents

shou1 be active in basic solutions and have good thermal

stability. 3Especially preferred are those wherein Z is anionic. Particularly useful fluorinated hydrocarbon wetting agents of this type are a01d under the trade name Fluorad by the Minnes- ota Mining and Manufacturing Company, St. Paul, Minnesota, and include species such as Fluorad PC-95, FC-98 and PC-128, with 0 a

.0 PC-95 and FC-128 being preferred and FC-128 being most pre- ferred. It4 Example 8

.00.a An aqi~teous alkaline permanganate solution was formed 6* If

It consisting of 60 grams/liter KMnO 4 38 grams/liter NaQE, and

water. The solution was divided into seven treating b,.aths. too.*: of S

0004 Wetting agent was added and properties of the baths determined as indicated in Table VIII. Table VIII

Bath No. Wetting Agent Surface Tension Sp.Gr. pH

(grams/liter) (dynes/cm)

I none 77.5 1.060 13.40

2 .01 P0-95 58.0 It

.0 5 44.0 I 3

.1 38.5 t 4 q .2 32. 32.0

6 -1 FC-128 35.0 It 13.45

7 .2 it t 25.2 it

Y,,oxy-impregnated samples were water-blasted and

immersed with constant agitation in the above baths with the

results iThdicated in Table IX. immersion time was forty minutes

Io 7 and the baths were maintained at 60 C.

Table IX

Bath No. Percent Weight Loss

(x 103 1, 6.3

6.6

6.6

6.9

7.2 0 4 a. 0* 0

aS S 7.4 a. ~0 S a a Example 9 a *0 a S 0 The procedure of Example 8 was followed, except a. 0 S 0 that the samples were not water-blasted prior to immersion and& there was no agitation.. Table X S. a S Ba* a Bath N~o. Percent Weight Loss a. a 5*W (x 10 3 a a 1 .2 a

20 2 2.2

S. 3 3.2 a a 4 2.2

3.4

6 3.3

7 3.7

Example

Trhe procedure of Example 9 was followed, except that the samples were agitated at the beginning of the Jmmer- sion witth no further agitation.

W Table X3:

Bath No*. Percenit Weight Losn (x i0 3 4.9 4.7

5.2

cx~ 5.7 4. 7 0@ S S 5 9 10 5.8 4. V 54 55 S

*4 55 0 B 4 0 5

.5 S S S

S. B S B S .5

#5 S S 5S4 S

S. F S F

4 0

A

~S S S

Claims (1)

1. The claims defining the invention are as follows: 1. In a process for the manufacture of articles com- prising at least one hole formed in resin-containing materials, the improvement in cleaning smears of resin from the barrel of

   said hole consisting of contacting said hole barrel with an

   alkaline permanganate solution having a pH of at least about 4 13 and an elevated temperature/for a period ranging ftom about Aa kC" twenty to about fifty minutes. 2. The process of claim 1, wherein said pH is from

   about 13.4 tr about 13.5 and said contacting period ranges to from about thirty to Lbout forty-five minutes.

   o3. The process of claim 2, wherein said alkaline per-

   manganate solution is an aqueous solution comprising potassium

   9 permanganate and a strong base. 4. Th.- proce ss of claim 3, wherein said aqueous sol-

   ution also includes a wetting agent.

   5. The process of claim 4, wherein said w,'tt .ng agent

   is a fluorinated hydrocarbon.

   6. In a process for -e manufacture of articles com-

   prising at least one hole formed in resin-containing materials,

   the improvement in cleaning smears of resin from the barrel

   of said hole consisting of contacting said hole barrel with an aqueous solution comprising from about 20 to about 60 grams/

   liter potassium permanganate and about 40 grams/liter sodium

   hydroxide, wherein said solution is at an elevated temperature

   of from about 40°C to about 60 0 C and the period of said con-

   tacting is from about twenty to about fifty minutes.

   7. The process of claim 6, wherein said solution

   includes a wetting agent.

   The pr'-_s 7 of claim 7, wherein said contacting

   t 16- period is from thirty to forty-five minutes. 9. The process of claim 8, wherein said wetting agent comprises from 0.01 to 0.2 grams/liter of a fluorinated hydrocarbon. The process of claim 9, wherein said aqueous solution comprises 60 grams/liter potassium permanganate, grams/liter sodium hydroxide and 0.2 yrams/liter 2luorin- ated hydrocarbon wetting agent and said elevated temperature is about 600 C. 11. In a process for the manufacture of articles comprising at least one nole formed in resin-containing mat- 04 erials, the improvement in cleaning smears of resin from the a barrel of said hole consisting of contacting said hole barrel with an alkaline permanganate solution having a pH of at least 13 at an elevated temperature above room temperature for a period of time sufficient to remove said smears of resin

   *a and essentially terminating prior to the second weight-loss period of th cleaning cycle, said period ranging from 20 to 0* 0* U a 0 50 minutes. 12. The process of claim 11, wherein said alkaline permanganate solution has a temperature of at least 400 C. 9

   13. Ths process of claim 12, wherein said alkaline permanganate solution is an aqueous solution comprising potas- 00

   siwi permanganate and a strong base. 14. The process of claim 13, wherein said solution includes a wetting agent.

   r 15. The process of claim 14. wherein said wetting agent comprises a fluorinated hydrocarbon. 16. The process of claim 15, wherein said solution

   is at a temperature of 60 0 C.

   *444 @440 S@ O' 0 4* 00 0* SR a 0. S *e

   S 0 0 3 4 0 0 *00 0 @0 0 0 a 0 0 0 0.00 900 0 '0 4 40* 03 4404 *4* 0* 0 30

   86,32S 8-7s least one hole formed in a wire assembly circuit board for adherent metallization by contacting the barrel of said hole with an alkaline permanganate solution having a pH of at least

   -bee 13 and an elevated temperature/for a period of time

   sufficient to remove resin smears from said barrel, with said

   period essantiall terminating prior to the second weight-loss t^C-t- t jo yv >o -tcnO iO period of the cleaning'cycle 18. The process of claim 17, wherein said elevated o0 IO temperature is from- alemat 40 C to-ev*®.

   19. The process of claim 18, wherein said contacting

   period is from ab~wk thirty to -ae forty-five minutes.

   20. The process of claim 18, wherein said pH is from

   S: abet 13.4 to aelte 13.5.

   21. The process of claim 20, wherein said solution

   also comprises a strong base.

   22. The process of claim 21, wherein said solution

   compriseA water, a-bui 60 grams/liter potassium permanganate,

   and 6d1t 38 grams/liter sodium hydroxide, with the temperature

   of said solution being "am

   23. The process of claim 22, wherein said solution

   includes a wetting agent.

   24. The process of claim 23, wherein said wetting ag-

   ent is a fluorinated hydrocarbon.

   In a process for the formation of a wire assembly

   circuit board, the improvement for insuring a good conductive

   joint between the tip of an intersected wire and the vall of

   a hole in said board intersecting said wire comprising the

   steps:

   a. treating said hole according to claim 17 so as to

   A \simultaneously remove zesin smeared in the barrel of said hole

   L 6i

   7" 7 and etch insulation back from said intersected wire tip. and b. metallizing said hole and intersected wire tip, thereby insuring a final joint in which the intersected wire tip is firm imbedded in the metallized hole wall. 00 C-4 o DATED this FOURTH day of NOVEMBER, 1975

   00 KOLLMORGEN CORPORATION

   Patent Attorneys for the Applicant 0* SPRUSON FERGUSON

   e

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   9

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