CA1139011A - Edge clip terminal for mounting thick film hybrid circuits in printed circuit boards - Google Patents

Abstract

D-24,330C

EDGE CLIP TERMINAL FOR MOUNTING THICK FILM HYBRID
CIRCUITS IN PRINTED CIRCUIT BOARDS
By Paul R. Ellis, Jr.

ABSTRACT OF DISCLOSURE

An improved edge clip terminal having a diamond-shaped transition region connecting a plurality of tines, that clip over the edge of a substrate, to a first lead section and having a second diamond-shaped transition region connecting the first lead section to a second lead sec-tion. In an assembly, the second lead sections of a plurality of term-inals are located in holes in a PC board with the second transition regions resting on the surface of the circuit board. The first lead sec-tions are more narrow than the transition regions and of lengths that are sufficient for preventing solder wicking up them and into the areas of the tines during wave soldering of a circuit board so that a leaded substrate soldered into the circuit board may be tilted without damaging it.

Description

:: ~ 9~

D-24,330C

: 1E~GE CLIP TERM~AL FOR MOUNTI~ THICK FILM HY~RID
2CIRCUITS IN PRI~nED CIRCUIT EOARDS

This is a division of Canadian application 342,519, filed 6 December 21, 1979, in the name of GTE ~.utomatic Electric 7 Laboratories Incorporated.
8 FT~r~D OF INVENrION
9 This invention relates to the manufacture of electrical circuit assemblies and mDre particularly to apparatus for flexibly m~unting a 11 thick film hybrid substrate with leads thereon soldered in plated-through 1~ holes of a printed circuit board so that the substrate can be tilted in a 13 plane orthogonal thereto without damaging it.

D~SCRIPTION OF DRA~ING
16 This invention and prior art structures will be more fully un-17 derstood from the f`ollowing detailed descrlptions that make reference to 18 illustrations in the drawing where: FIG. 1 is a perspective view of a 19 conventional terminal strip 5 carrying a plurallty of edge clip terminals 7; FIG. 2 is a right side elevation view of a hybrid circuit assembly 20 21 having terminals of a strip 5 clipped over the bottom edge 34 of a sub-22 strate 22, with the carrier bar 16 removed frorQ the terminal strip; FIG. 323 is a front elevation view of a hybrid circuit 20 supported .~n a printed 24 ¦ circuit board 50 ln accordance with this invention; FIG. 4 is a perspec-25 ¦ tive view of the structure in FIG. 3; and FIG. 5 is a front elevation view 26 ¦ of a portion of a hybrid circuit 20' supported in a circuit board 50' in 27 ¦ accordance with a n~dified form of this lnvention~ In order to n;ore 28 ¦ clearly illustrate structural detail here, the figures are not drawn to 29 ¦ scale.

~3. ,~r~
L~~2~, 330C

1 DESCE`~IPTION OF. PRIOR I~RT

2 The thlck :Film hybrid circuit 20 in FIGS. 2

3 and 3 is conventional (except for the beads 70 in FIG. 3) and comprises a rectangularly shaped glass-ceramic substrate 22 hav-5 ing a resistor 2~ and conductive pat-terns of lines 26 and lands 6 28 formed on one side 30 thereof; a transistor 32; and edge 7 clip terminals 7. In one method of manufacturing such hybrid 8 circuits, tines 11-13 of terminals 7 in an edge mounting term-9 inal strip 5 in FIG. 1 are snapped over the bottom edge 34 of 10 the substrate 22 as is shown in FIG. 2. The terminal strip is 11 stamped out of a sheet of 0.010 inch thick brass, for example, and 12 tin plated, the leads ~ being typically 0.020 inch wide and term-13 inating on a diamond shaped transition region 9 having a width of 14 0.060 inch, a tapered section of leng-th Ll = 0.030 inch, and 0.050 15 body of leng-th L2 -/inch. The terminal strip 5 and subs-trate 16 (not includihg the -transistor 32) are then dipped in molten 17 solder to electrically connect front tines 11 to associated lands 18 28A-28F. This also tins the terminal leads 8 and conductive 19 pat-terns on the substra-te. A~ter connecting transistor 32 in the 20 circuit 20 by re~low soldering, the carrier s-trip 16 is removed 21 and the free ends of leads 8 are inser-ted in-to associa-ted ones of 22 the plated-through holes 52 in a printed circui-t mother board 23 50, as is generally illustra-ted in FIG. 3 excep-t for the beads 24 70. The terminal strips 5 were designed to locate leads 8 in 25 circuit board holes having a diameter that is only sligh-tly 26 greater than the width of the leads. In such an application, 27 the transition regions 9 of clip terminals 7 provide a stand off 2~ between a substrate and a circuit board -that is approxima-tely eq~al 2~ to the sum of the lengths Ll and L2 in FIG. 1. In order to ~0 D-2~1, 330C
,~

1 facilitate insertion of leads 8 into holes 52 of circuit bo~rds 50 in a manufacturing opera-tion, however, the holes ~2 are made 3 about 0.042 inch in diameter which is typically greater than twice the broadest dimension of the leads. This causes the major 5 portion of the ]ength Ll o~ tapered sections of transition 6 regions 9 to be located in circuit board holes 52 and allows -the 7 subs-trate -to tilt as much as 45. Since leads 8 and transition regions 9 of -terminals 7 are now tinned, solder wicks up leads 9 8 and around -tines 11-13 and transition regions 9 in FIG. 2 10 during wave soldering to rigdly fix the position oE the substrate 11 in -the circuit board. It has been discovered that this inflex-12 ible mountin~ of a substrate is a principal reason for hybrid 13 damage such as fracturing of a substra-te by an operator bending it 14 out of the way of other parts/during flexure of the circui-t board.
Although the support in U.S. Patent 4,089,0~2, 16 issued r~ay 9, 1978,of Roy s. Torburn, provides a s-tandoff between 17 a hybrid substrate and a circuit board, modi:fication of a circuit 18 oard is required to use it. Also, considerable surEace area oE
19 a board mus-t be free of other components in order to use -tha-t 20 support which rigidly fixes -the position oE a subs-trate.
21 Specially molded sugar cubes have previously been located on leads 22 of relatively light elements such as transistors -to provide s-tand-23 off during soldering of transistor leads to traces on a circui-t 2~ oard. They are unsatisfactory for providing standoff ~or sub-25 strates, however, since the porous sugar cube absorbs liquid ~6 ~lux which is applied to terminal leads to Eix their position as 27 the leads are inserted into holes on a circuit board. Also, this 28 requires the itional step of washin~ the assembled substrate 32 _ 3 _ ~ 21~,330C

1¦ and circuit board in water to dissolve and remove th~ sugar cubes, and 21 then drying the assembly. ~lax beads impregnated with a g;Lass powcler have31 also been used for holdi-~ relative`Ly light components such as a t~ransi 41 tor of'fset from a circuik board during a solder operation. They are also 6 unsatisfactory for providing standoff' o~ substrates since the wax members 6 sublime at room ternperature and are softened by liquid flux which is ab-7 sorbed into the structure. m is makes it difficult to llse them in a pro~
8 duc-tion operation where a h~brid substrate may sit fbr a period of time 9 prior to its assembly into a circuit board and wave solderlngr The flux in the wax also makes it difficult to clean the latter of'f' Or an assembly 11 with Freon after a soldering operation. Further, since the hybrid sub-12 strate is relatively heavy and has its weight concentrated across a narrow 13 edge of a substrate, it tends to collapse the wax member which sortens 14 considerably during a wave solder operation.
An obJect of thls invention ls the provision of' apparatus for 16 mounting a hybrid substrate in a circuit board with a prescribed standoff.
17 Another obJect is the provls:lon of apparatus ~'or f:Lexibly rnountiry~ a hy-18 brid su.bstrate in a circuit board so that the substrate rnay be tllted 19 w:Lthout dalnagi~yr it.
21 S~ RY oF I~E~TION
22 In accordance with this invention, an improved edge clip termi 23 nal, for rnounting a hybrid substrate on a rnother board having holes there~
~4 in that are associated with conductive material on the board, comprises:
a plurality of tines on one end thereof rOr clipping over the edge of a 26 substrate; a pair Or lead sections; a f'irst transition region connecting 27 the tines to a first one of the lead sections which has cross-sectional 28 dimensions that are rnuch smaller than those of' the first transition re-29 ~ion; and a second transit.ion region -~rterconnecting the pair of lead sec-tions whlch have dimensions in cross~section that are rl~uch srnaller than 31 ¦ those of the first and second transi.tion regionC; the ~ree end of' t~le sec-32 ond one of' the lead sections beir~ inserted into a ho:Le ln the boc~d and ¦ soldered to conductive mlateria.l, with the second trc~nsit:Lon region con-_4.

D-2~,330C

1 tacting one of concluctive rnaterial on and a surf`ace of the bo.~rd for ~up-2 porking the leaded substrate and f'lrst lead section a~ove the ~oard so 3 tha.t the leaded substrate rnay be tilted without damagir~ it. And in an another embodiment, an improved edge clip terminal for r~unting a hybrid substrate on a mother board having holes therein that are associated with 6 conductive material on the board comprises; a plurality of tines on one 7 end thereof for clipping over the edge of a substrate; f'irst and second 8 lead sectlons; a first transition region connectng the tines to the flrst 9 lead section; and a second transition region interconnectin~ the first and second lead sections which have dimensions in cross-section that are much 11 smaller than those of the first and second transit.ion regions; the free 12 end of the second lead section being adapted :~or insertion into a hole in 13 the board and for being soldered to conductive material thereon, with a 14 dimension in cross section of the second transitlon being ~reater than the breadth o.f the hole for contacting conductive material or a surface of the 16 board for supporting the leaded substrate and first lead section above the lq board. In a preferred em~diment, the length of the second transition re-1~ gion is sufficient to prevent rr.olten solder wiclc:Lng up the ~irst lead sec-19 tion and first transition region and into the area of the tines clurir~ a wave solder operation so that the leaded substrate may be tilted without 21 dc~r~ging it. In an alternate embodimellt, the length of the first lead 22 sect:ion is sufficie,nt to prevent nDlten solder in a wave solder operatlon 23 wicki.ng up onto the tines and :~r allowing bending of -the first lead sec~
24 tion for tilt~ng the leaded substrate.

26 D~SCRIPTION OF PRE~E~,D ~o~E~rs ~_ _ 27 Hybrid circuit assemblies 20 having clip terr~nals 7 soldered 28 ¦ thereto are normally stored in trays (not shown) in their -lnverted posi-29 ¦ tion (which is opposite to that in FIG. 2) prior to asser~bly in circvit 30 ¦ boards 50 havirlg plated-throu~,h .holes 52 associated with conductive traces 31 ¦ 511 on the underside thereof~ ~hile a h,ybri.d circui.t 20 is i.n its inverted 32 ¦ posltion, apertured be,ads 70 are located over the end or outerlr.ost leads 8A and 8~ -thereof'. A drop of I.iquid rosi.n flux is ~,hen placed cn :?.l~.`h of ~L~39ell , D_2LI,330C

1 the end leads at a point adjacent the aperture -Ln the bead so that this 2 ~lux runs along the leads and lnto the bead apertures. The f~lux is 3 allowed to dry in the apertures of beads 70 so that they will not fall orf

4 of 'Leads when a beaded hybrid circuit is held in c~n upright position.
me apertures through the beads 70 are pref'errably only slig~ltly 6 larger than the largest cross-sectional dimension of leads 8 so that the 7 beads slide smoothly onto leads and a ~sma~l amount of f'lux flows into the 8 apertures. By way of example, the diameter of apertures is approximately 9 0.023 inch for beads used on OoO10 inch thick leads that are 0.020 inch wide This allo~s the tapered section of a transition region to drop only 11 a few thousandths Or an inch into the aperture of a bead. The beads 70 12 are heat resistant and hard enough to support a substrate 22 in a wave 13 solder opera-tlon. r~hey are also relatively non-porous so that the liquid 14 flux is not absorbed into them. Further, the beads are brittle so that they are readily fractured, as is described more f'ully herelnafter, when 16 it is desirable to remove them from a circuit assembly. Beads meeting 17 these criteria may be cylindrically or spherically shaped and made of 18 glass or ceramic material.
19 Peaded llybrid circuits are individually removed from a storage tray and held in their upright position as the f'ree ends of leads 8 are 21 inserted into holes 52 of a circuit board 50 (see FIG. 3). Each stuf'fed 22 circuit board 50 is then loaded in a carrier (not sho~) and passed 23 through a wave solder operatLon in the conventional manner to solder leads 24 8 into associated ones of' the plated-through holes 52 and to traces 54 on the board. The height H of' beads 70 is selected to hold a substrate 26 spaced above the top surface 56 of a clrcuit board so -that a portion of 27 the narrorw leads 8 is located above the board. r~Ore speclf'ically, the 28 thickrless of' beads is selected to hold the tapered sections on transition 29 regions 9 at least 0.050 inch above the circuit board so that solder will n{,t wiclc up leads and lnto the area of the tines and transltion regLon o-f 31 a ter~inal when the aperture in a bead is much l~rger than the thlc~ness 32 or ~.vldth Or a ad.

D~24,330C

1 ~he soldered circuit hoard may be cleaned in c~n agîtation type 2 Freon bath to rernove ~lux therefrom. Durlng an inspectlon and touch-up 3 operation of a soldered circuit bocard 20, ~he point Or a thin~sharp in~
4 strumenk such cas c~n Xacto knlf'e is located in the top of the aperture in a ~ bead 70. Pressure is then exerted by l;he sharp knife edge of' th~ blade 6 onto the top edge of the bead in order to fracture it~ ~his operation is 7 repeated for all beacls on the hybrld circult 20. After the bead parts are 8 pushed away from leads, the soldered circuit ~oard is passed through a 9 second cleaning operation which removes the bead parts and any flux left on the beaded leads. In this mannerJ a h~ybrid circuit 20 is flexibly 11 mounted on a circuit board 50 so that it can be tilted about the line A---A12 in ~IG. 4 without damaging it.
13 In a ~.odified form of this invention in FIG. 5, each lead of 14 terminals on a hybrid 20' is divided into two sections such as 8At and 8A" , with a second transition region such as 9Ai being located between 16 the th~ lead sections. The tapered section on a lower transition reæion 17 9A' is seated in a hole of a circuit boc~rd 50'. The length L3 of' the leac~
18 section oA'1 space,s the tWD transltion regions 9A and 9A' at least 0.050 19 inch apart to keep solder from wicking up over the 'lower tr~nsiti.on re-gions and onto the tines of terminals. Alternat:Lve:Ly, each le~ o~ a hy-21 hrid ci.rcuit 20 may have at least two serpentine bends i~ it which are 22 linearly spaced approximatel~ 0.050 inch apart, the lower bend COrltaCtir~
23 the top of the circuit 'board for spacing the upper bend sufficiently 24 therefrom for preventir~ solder w~Lcking up leads and rigidly fixing the position oP the hybrid circuit during wave solder operat:'Lon.
26 Althou~h this invention ls described in relation to pre:~erred 27 embodiments thereof, variations and nDdifications will occur to those 28 skilled :Ln the art. By way of example, the beads rnay ~e cylindrlGally 29 shaped ferrite cores or slugs, truncated spher-lcally shaped r~ernbers~ or nor,-sy~nlet~ically shaped members. Also, t;h~e cross~sect:lons o.f apertures 31 ~ka~ ~e other than circular and apertures may be ~paced f'rom the center o~32 beads, although it ls necessary that apertures exter.d subst;ant:lally 1~`3.~ 1_24,330C

1¦ straight -through thern. Additl~nally, the circui~ 20 may be other than a 2¦ ~hi.ck film circuit and be r~unted .Ln a structure other than a printed cir-3 cuit board. Alsog t~le beads may be prevented rrom falling of'f o~ the 4 leads 8 by paste flux or whike glue. Fur-ther, the beads may be left on the leads arld located on other than the end leads. The scope of thls in-6 vention is there~ore de~ermined by the attached cla~ms rather than from ~ the sforement ed detalled desoript1on~

;6 31 ~-~ " ,, -. .

Claims (6)

1, An improved edge clip terminal for mounting a hybrid sub-strate on a mother board having holes therein that are associated with conductive material on the board, comprising:
a plurality of tines on one end thereof for clipping over the edge of a substrate;
a pair of lead sections;
a first transition region connecting said tines to a first one of said lead sections which has cross-sectional dimensions that are much smaller than those of said first transition region; and a second transition region inter-connecting said pair of lead sections which have dimensions in cross section that are much smaller than those of said first and second transition regions;
the free end of the second one of said lead sections being in-serted into a hole in the board and soldered to conductive material, with the second transition region contacting one of the conductive material on and a surface of the board for supporting the leaded substrate and first lead section above the board so that the leaded substrate may be tilted without damaging it.

2. The terminal according to claim 1 wherein at least one cross sectional dimension of the second transition region is greater than that of holes in the board.

3. The terminal according to claim 2 wherein the length of the second transition region is sufficient for preventing molten solder wick-ing up said first lead section and first transition region for rigidly fixing the position of a substrate in a board for generally preventing tilting of the substrate without damaging it.

D-24,330C

4. The terminal according to claim 3 where-in the length of the first lead section is sufficient for preventing molten solder wicking up onto said tines and for allowing bending of said first lead section for tilting the substrate.

5. An improved edge clip terminal for mounting a hybrid substrate on a mother board having holes therein that are associated with conductive material on the board, comprising:
a plurality of tines on one end thereof for clipping over the edge of a substrate;
first and second lead sections;
a first transistion region connecting said tines to said first lead section; and a second transition region interconnecting said first and second lead sections which have dimensions in cross-section that are much smaller than those of said first and second transition regions;
the free end of said second lead section being adapted for insertion into a hole in the board and for being soldered to conductive material thereon, with a dimension in cross-section of the second transition region being greater than the breadth of the hole for contacting conductive material or a surface of the board for supporting the leaded substrate and first lead section above the board the length of the second transition region being sufficient to prevent molten solder wicking up said first lead section and first transition region and into the area of said tines during a wave solder operation so that the leaded substrate may be tilted without damaging it.

6. An improved edge clip terminal for mounting a hybrid substrate on a mother board having holes therein that are associated with conductive material on the board, comprising:
a plurality of tines on one end thereof for clipping over the edge of a substrate;

D-21,852 first and second lead sections;
a first transition region connecting said tines to said first lead section; and a second transition region interconnecting said first and second lead sections which have dimensions in cross-section that are much smaller than those of said first and second transition regions;
the free end of said second lead section being adapted for insertion into a hole in the board and for being soldered to conductive material thereon, with a dimension in cross-section of the second transition region being greater than the breadth of the hole for contacting conductive material or a surface of the board for supporting the leaded substrate and first lead section above the board; the length of the first lead section being sufficient to prevent molten solder in a wave solder operation wicking up onto said tines and for allowing bending of said first lead section for tilting the leaded substrate.