DE2143809A1 - Process for producing supply frames - Google Patents

Description

Dr. phil. G. B. HAGEN

Patent attorney Λ <j / QQHQ

MUNICH 71 (Solln)
Franz-Hals-Strasse 21
Telephone 796213

AMP 2955 Munich, August 26, 1971

NS.

AMP Incorporated
Eisenhower Boulevard
Harrisburg, Pa., V. St. A,

Method of manufacturing lead frames

Priority; Sept. 8, 1970} V.St.A.} No. 70 034

The invention relates to a method of manufacturing lead frames.

A transistor lead frame is known which has a relatively has massive heat sink on which a transistor or semiconductor die is attached, as well as three supply lines, which are at a distance from the plane containing the heat sink and in a parallel to it Are arranged level. The middle or collector lead is connected to the heat sink, and the end sections of the outer leads extend over the surface of the heat sink and are bent backwards towards each other, so that their tips lie between the two planes. The transistor is below the tip sections of the outer Leads arranged, and these tips are connected to the contact portions of the semiconductor die, wherein the middle lead serves as a collector for the transistor.

Such lead frames require leads from relatively thin bar metal. They also require Bayerische Vereinsbank München 820993

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a relatively strong heat sink, so that the necessary heat distribution property is given. It is common so far been, such lead frames from two separate Make strips that are then joined together. The heat sinks are made by punching out a relatively strong metal strip, and the leads are made by punching and forming a relatively thin strip. Then the collector lead assembled with the heat sink by means of a bracing process or another mechanical fastening process.

A method for manufacturing lead frames in the form of a continuous strip is characterized according to the invention in that a metal strip is stamped out so that a sequence of frame blanks lying next to one another is formed, each blank having a heat sink and three spaced parallel leads which extend transversely with respect to the longitudinal axis of the metal strip, the middle of the supply lines being connected to an edge of the heat sink via a connecting web and the outer supply lines each having a contact arm at one end adjacent to the heat sink and the contact arms extending along the length of the metal strip, extend in opposite directions and the supply lines are connected to one another by means of a connecting web formed in one piece therewith, that the arms are bent laterally to the plane of the metal strip, that the connecting part at a point remote from the edge d he heat sink is bent so that the leads are pivoted in a curved path and are oriented in a queijfeur plane of the metal strip extending plane, with the arms on one side of the heat sink and the free ends of the leads are arranged on the opposite side, that the arms essentially in their end

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valid configuration and that the connecting part is bent at a point near the edge of the heat sink so that the leads along a curved Pivoted away and oriented in a plane that is at a distance from and parallel to the plane of the metal strip extends with the arms positioned between said planes.

An embodiment of the invention is described below with reference to the figures. From the figures

Figure 1 is a perspective view of a punching and forming die set for the production of lead frames in strip formj

Figure 2 is a plan view of the die set of Figure 1, with parts of the upper die broken away, so that parts of the tooling are visible in the lower die;

Figures Top views of a strip continuously produced with the die set of 3A, 3B, Figure 1,

where the successive stages of shaping the lead frames are illustrated;

Figure 3C is a perspective view of a short Piece of a supply frame strip}

Figure 3D is a perspective view of a short Piece of sheet metal strip from which the lead frames are made;

FIG. K shows a plan view on an enlarged scale of the equipment of the lower die, which is used to originally bend the arms of the outer leads of the lead frames downwards;

Figure 5 shows a representation along the line VV of Figure k]

FIG. 6 shows a representation along the line VI-VI

of Figure 4, the positions of the upper and lower tooling prior to the initial bending and forming operations shown are carried out with the contact arms of the lead frames;

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FIG. 7 shows a representation similar to FIG. 6, but with the positions of the tool equipment are shown "when the equipment in the upper die engages downwardly with that in the Lower die has been enclosed and after that the bending and shaping operations have been carried out;

Figure 8 is a section along the line of Figure 2, with the die equipment on a bending station of the die is illustrated, in which all leads of the Frames are bent down from their original planes;

FIG. 9 is a representation similar to FIG. 8, but the positions of the parts being shown, after the initial feeder fuse operation has been performed;

Figure 10 is a view along the line X-X of Figure 2, with the equipment in the upper and Lower die is shown for further shaping the contact arms at the ends of the outer leads is;

FIG. 11 shows a representation similar to FIG. 10, the positions of the parts at the end of this arm forming process are shown;

FIG. 12 shows an illustration along the line XII-XII from FIG. 10;

FIG. 13 shows a representation along the line XIII-XIII from FIG. 11. j

Figure Ik shows a representation along the line XIV-XIV of Figure 2, showing the station at which the supply lines are bent back into a plane running parallel to the plane of the heat sink;

FIG. 15 is a representation similar to FIG. Ik , but showing the positions of the parts at the end of this second bending process;

FIG. 16 shows an illustration along the line XVI-XVI from FIG. 15 5

FIG. 16A shows a partial perspective illustration of an upper bending tool shown in FIG. 16;

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FIG. 17 is an illustration along the line XVII-XVII of FIG. 2, showing a molding station is on which a web part, which is between the central collector lead and the Heat sink extends, is bent to the outer leads centrally above the heat sink to position;

FIG. 18 shows a representation similar to FIG. 17, but with the positions of the parts at the end of this Shaping process are shown;

FIG. 19 shows a representation along the line XIX-XIX of Figure 2, with the tooling which is provided at a final sizing and forming station is;

FIG. 20 shows a representation similar to FIG. 19, but with the positions of the parts after they have been carried out of the last sizing and shaping process are shown; and

FIG. 21 shows an enlarged plan view of the tool equipment which is arranged according to FIG.

As FIG. 3C shows, a transistor lead frame 2 a relatively thick metallic heat sink 4, the solder on one surface and three relatively thin Leads 6, 8, 10 carries. The supply lines 6, 8, 10 are arranged in a plane that is parallel to the heat sink 4 plane runs at a distance from this. The middle supply line 8 extends from the outer edge l4 of the heat sink 4 and is bent backwards at the point 15 so that they have a Forms web part 12, which extends parallel to the heat sink 4 to the front over the same. The front end 13 of the footbridge 12 is bent back so that the supply line 8 extends at a distance from the web part 12 parallel to this. The outer leads 6, 10 have front ends 18 which extend over the top of the heat sink 4. the outer leads have at their ends 18 contact arms 20 which extend laterally in opposite directions

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stretch and which are bent down towards the heat sink and inwardly towards one another so that tips 2k of these arms extend in front of the web part 12 of the central supply line 8 and directly above the surface of the heat sink k . The arms 20 are covered with solder 26a in the manner shown. The tips 2k of the arms have a distance from one another which is significantly smaller than the width of the web part 12 of the central supply line 8. This distance is relatively critical, since the tips 2k of the arms 20 with the contact areas of a transistor plate, not shown, which is on the heat sink k is attached, to be connected. The äuße- ψ · reu supply lines 6, 10 are not directly connected with the heat sink k, however, are connected to the central supply line 8 in one piece by means of a transverse connecting web sixteenth

When a transistor, not shown, is assembled with the lead frame 2, the transistor or the semiconductor die is arranged on the surface of the heat sink k , the tips 2k of the contact arms being arranged adjacent to the contact areas of the semiconductor die. The semiconductor die has a thickness that is somewhat is greater than the distance between the tips 2k of the arms Λ and the surface of the heat sink, so that the semiconductor wafer is resiliently held in its position while the lead frame 2 passes through a soldering furnace in which the solder 26 on the surface of the heat sink k liquefies again to secure the die to the lead frame. The ends of the leads, the semiconductor wafer and parts of the heat sink are then enclosed in a housing in a molding process, the connecting web 16 serving as a mold closure or insulating web during the process. The between the supply lines. Stretching parts of the connecting web Ib are then removed by means of a punching process, so that the leads are electrically isolated from one another.

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As shown in FIG. 3Q, feeder frames 2 are made from metal strips 30 made, the one in cross section relatively thick portion 32 and a relatively thin portion 34, with on part of the surface of the thick portion 32 and an adjacent part of the thin Section 34 is a previously applied strip of solder 26 '. Metal strips of this type are made by rolling made of metal strips of uniform thickness. The metal is a copper alloy that is nickel-plated is; however, other metals can also be used.

A punching and forming die set 48 for producing a strip of lead frame 2 from metal strips 3O is now used with reference to FIGS. 1 and 2. The die set 48 has an upper die 50, a lower die 52 and guides 54. The die set 48 is designed so that it is in a conventional punch press that is in accordance with conventional stamping and forming techniques operates, can be arranged, and has lower and upper tooling 56 and 60, respectively, through which the metal strip 3O during movement between the dies 50, 52 is continuously molded. The lower tooling 56 is in individual blocks in a channel-shaped manner Mounted recess 58, which extends over the length of the Lower die 5- extends, as well as in further depressions, which will be described later, and the upper tooling 60 is similarly in the upper die 50 assembled. A generally channel-shaped recess 62 is provided which extends the entire length of the lower die 52 extends and through which the relatively thick part 32 of the strip 30 from which the heat sinks 4 are formed is fed. The supply lines 6, 8, 10 extend downward in FIG. 2 onto the front section 74 of the lower die 52 to so that it is guided past forming stations will.

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The initial punching operations in which the openings 36 » 38, 39, 40 and 42 (Figures 3A, 3B) are not shown, as conventional punching techniques are used for these processes can be applied.

After the initial punching operations have been carried out, the ends of the leads 6, 8, 10 are rounded with dies 64 which are arranged in a recess 66 and cooperate with suitable punches. This process is performed at station 62 (Figure 3A). Afterward the contact arms 20 'are bent down at the ends of the outer leads 6, 10 at a station 43, such as it is shown with reference to Figures 2, 3A and 4-7.

The lower tooling for this initial arm molding process is mounted on a pusher 70 which extends in one direction from the tape feed path to the front section of the lower die 52 is arranged extending groove, wherein suitable guides 76 are provided on each side of the slider 70 are to this exactly on the metal strip 30, the is guided by the die set 48, to and away from this. The slide 70 has a recess 80 in its adjacent to the front portion 74 of the lower die 52 End, and a pin 82 is mounted in the slide 70 and penetrates this recess. The slide 70 is moved a very small distance towards and away from the metal strip 30 by a cam rod 84 (FIG. 5), wherein the cam rod 84 extends from the upper counterbore 50 into the recess 80 and has baffles, which push the slide inward during the downward movement of the upper die 50 and it during the upward movement retract the upper die 50.

According to Figure 6, the arms ^ O ^{1 of} each die cut passing through the forming station 43 are bowed over a clamping block 88,

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which is mounted on one side of the front end of the slider 70, with a recess 86 provided under the block 88 so that the bending operation described below can be carried out. After the metal strip 30 has been fed in, the web part 12 of the central supply line 8 lies on the surface of the block 88, and the end sections of the arms 20 ′ extend laterally beyond the sides of this block 88. A clamping block 90 is arranged in the upper die 50 and is resiliently biased downwards by means of a spring 92, so that the middle web section 12 and the ends 18 of the supply lines 6, 10 are firmly clamped during the downward movement of the upper tool equipment, as FIG. 7 shows. The laterally protruding contact arms 20 'are then bent downwards against the sides of the block by means of a bending tool 93j which has legs ^ k located at a distance from one another, this bending tool 93 surrounding the clamping block 90. At the end of this bending process, the arms 20 ′ are bent downwards and lie against the sides of the clamping block 88.

During the subsequent upward movement of the bending tool 93, the clamping block 88 is withdrawn from below the partially formed contact arms 20 'so that the metal strip 30 can be continued to the left in FIGS. 6 and 7 for a further forming process. At the next forming station, which appears on the left in FIGS. 6 and 7, the arms are bent inwards over a mandrel 96 with profile sides 98. The mandrel 96 is also mounted on the inner end of the slide 70 and between a pair of forming arms 100 which are disposed in a recess in the slide and are pivotable on a common pivot pin 102. The arms 100 are normally biased away from each other by a spring IO6 and have inner ends which spread laterally from the mandrel 96 so that when the slider in his

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front or inner position, these arms on each side of the downwardly extending contact arms 20 * of the leads 6, 10 are. The opposing surfaces of the forming arms 100 are curved at 108 so that that when the arms are towards each other and against the sides 98 of the mandrel 96 are moved, the contact arms 20 'inward be bent, as shown in Figure 7 on the left. Note that after this inward bending of the contact arms 20 'these remain apart by a distance which is greater than the width of the Web part 12 'of the middle supply line 8.

The forming arms 100 are actuated by a cam follower 114 located in the upper tooling 50 and has inclined surfaces 112 which act on surfaces 110 of the arms 100, as can be seen from Figures 6 and 7, so that the arms 100 against the force of the bias spring IO6 close. A hold-down block II6 is in a central one Passage mounted in the cam follower Il4 and is resiliently biased downward by a spring II8 and tensioned the 1st web part 12 'and the ends l8 of the supply lines 6, 10 firmly.

After the second Armformungsvorgang according to Figures 6 and 7, the slide 70 is withdrawn and the mandrel 96 moves from below the formed contact arms 20 'away, so that the metal strip 30 the following molding stations can be supplied. Since the contact arms 20 'now extend downwards and below the plane of the metal strip 30, a recess or groove 124 is provided for the contact arms extending downwards, as FIG. 8 shows.

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Reference is now made to FIGS. 2, 3A / 3B. Further punching operations are carried out at a station 120 in order to remove the remaining finger-like section 121 between adjacent lead frames 2. The embossing operation for forming the sides of the heat sink can also be performed at dex station 122. Since this herkömmli-che Qesenkformvorgange are the tooling is not shown in detail, however, the stamping and punching dies can be seen in FIG. 2

According to FIGS. 8 and 9, the web part 12 'of the central supply line 8 is bent at the front end 13 so that the free ends of all supply lines 6, 8, 10 are pivoted downwards along a path of curvature, while the front ends l8 of the outer supply lines 6, 10 and the contact arms 20 'extending therefrom are pivoted inwardly along a path of curvature relative to the lower die 52. This bending process is carried out at station kk (FIG. 3B) by means of a bending tool 132 mounted in the upper die 50, a recess 126 being provided in a die block 128 so that a downward movement of the supply lines is possible. A mold plate I30 is arranged on the right side of the recess 1h6 (in FIG. 8) in such a way that its surface I3I bears the connecting web 12 ′ of the central supply line 8. The bending tool 132 has a relatively narrow projection 13 ^ on its forward-facing side, which is located above the underside 133 of the tool I32. While the bending tool 132 is being lowered, the supply lines 6, 8, 10 are pivoted downwards along a curved path until the underside of the projection 13 ^ moves against the surface of the connecting web 12 'of the central supply line 8, as FIG. 9 shows. The leads then extend in a vertical plane, and the contact arms w0 'are arranged above the plane of the heat sink k ' - *, as can be seen from FIG.

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ΛΑ ** ?; ■ '; ■ *

As shown in FIGS. 3B and 10-13, the ends of the Contact arms 20 'then bent inward and receive theirs final shape at station 45 by tooling comprising a slide I38 and a punch l40, both of which form part of the upper tooling 60.

The punch l40 has in its forward-facing side (Figure 13) a channel-like recess 142, whose width is substantially equal to the distance between the outer surfaces of the contact arms 20 ^r. When the punch 140 is lowered during the downward movement of the upper die 50, the slide 138 moves to the left in FIG. 10 and towards the punch 140. The slide I38 has at its front end a recess 144 and profile surfaces 146 which move against the outer surfaces of the contact arms 20 'and bend these arms inward until their tips 24 have the above-mentioned predetermined distance from one another, which is less than the width of the Bridge 12 '. The slider I38 has a plate 148 on its top which bends the contact arms 20 'downward and encloses them during the final forming and bending process. The slide 138 Tf is operated by a slide block 150, which in turn is mounted in a recess in the lower die 52 and can be moved to and fro by means of a cam rod 152. The cam rod 152 is mounted in the upper die 50, as already described with reference to FIG.

After bending the contact arms 20 'inwards according to FIGS Figures IO-I3, the connecting web 12 'is again on the Point 15 adjacent to the edge 14 of the heat sink 4 bent at an angle of 90 degrees so that the leads then pivoted through a 90 degree angle along a path of curvature are and lie in a plane which runs above the plane of the heat sink 4 and parallel to it. After this

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BAD ORIQINAi.

The second bending step, which takes place at station 46, is the surface parts of the ends 24 of the contact arms onto which previously solder was applied, to be directed to the surface of the heat sink 4, so that they with the not shown Semiconductor wafers can be soldered. The tooling to perform this second bend on the connecting web 12 'is shown in FIGS. 14-16 and has an upper bending tool 157 and a lower bending tool 162 formed in one piece with a block I60 is that in a slot Ιοί in the lower die 52 is mounted. A recess I56 in the lower tooling is provided in Figure 14 on the left side of the block 160, so that a free space is created for " the leads when pivoted along a curvature path, as can be seen from a comparison of Figures 14 and 14 15 can be seen. In its rest position, the sliding block 160 lies below the underside of the heat sink and the bending tool 162 lies on the underside of the connecting web 12 of the lead frame. The upper bending tool 157 has generally parabolic recesses 157a on its left side (in Figures 15 and 16A) extending through a vertical extending rib I58 are separated from each other. The rib 158 has laterally extending foot parts at its lower end 158a, so that the rib meets the connecting web 12 'of the lead frame restrained, but a curved movement of the shaped arms 20 'from the positions of FIG 14 in the positions of FIG.

Venn the upper bending tool 157 downward and the slider 160 move upwardly, the connecting web 12 'is given a sharp right angle bend 15, which causes the curved movement of the leads. The upper bending tool 157 is biased by spring force and strikes the lead frame with its lower end before the slide 160 moves upwards, see above

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that the heat sink 4 and the central supply line 8 firmly clamped before the bending process begins.

The bending tool 162 and the block 160 are moved to and fro by a lever 170 (FIG. 14). A pin I68 penetrates a slot 166 in the lower end of the block 160 and is received in an open-ended slot I69 in the lever 170, the lever being located in a recess I72 in the lower die 52. The right end of the lever 170 is pivotally connected at 174 to a rod 176 which strikes the surface of the lower die 52 and is biased upward (in Figure 14) by a spring 178 'seated in a recess in the die and against the bottom of a screw at the top of the rod acts. The shape of the lever 170 and the dimensions of the recess 172 in which it is located are such that when the rod I76 is pushed down by a push rod I80, the block I60 and the bending tool I62 upward from the position of FIG 14 can be moved into the position of FIG. The push rod I80 is mounted in the upper die and has a length such that an upward movement of the slide block I60 takes place after the upper bending tool 157 engages the heat sink and these clamps, as already described.

According to Figures 17 and 18, the connecting web 12 ' the middle lead 8 then further shaped to increase the bending angle at 13 and 15 until the connecting web 12 'is inclined between the leads and the Heat sink 4 extends defined planes, whereby the ends of the contact arms 20 exactly at predetermined locations the surface of the heat sink 4 come to rest. This bending process is carried out by means of a slide 184, which is carried by a block I86 over which the metal strip 30 and which forms part of the channel 62 for the heat sink 4 of the strip 30. The slider

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has an undercut I90 and a tip I9I on one End, so that when the tip 191 is moved to the right (in FIGS. 17 and 18) against the connecting web 12 ', the lead frame is given a Z cross-sectional shape. To the positions of the To monitor supply lines, an upper tool 182 is provided, which has a recess I88 at its lower end, which includes the end portions of the leads 6 and 10 during this process and all three leads holds in a horizontal position.

The slide 184 extends to the left in Figures 17 and 14 is attached to a sliding block I92, which is in a recess is mounted in the lower die 52. Back and forth movement is achieved by means of a cam rod in the Obergopeiik 50 is mounted and the above-described Nockenstangeii is designed similarly.

After completion of the shaping process according to FIGS. 17 and 18, the heat sink 4 has essentially its final shape. However, in order to accurately monitor the dimensions of the finished parts, it is desirable to perform a final sizing operation in which an upper sizing tool I98 is moved against the surfaces of the leads and continues to bend the connecting web 12 'until the leads are at the surface of a gauge block I96 issue. The exact distance between the planes of the heat sink k and the leads 6, 8, 10 is determined by the dimensions of a projection 200, which extends downward from the dimensioning tool 198 and moves against the surfaces of the leads, as FIG. 20 shows.

An important feature of the method described above is the manufacture of a lead frame in which the i of the contact arms 20 are at a distance from one another,

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which is substantially less than the width of the connecting web 12, and wherein the length of these arms, measured along the curved sections, is greater than that
Distance between the two planes of the heat sink 4 and the contact arms 20. It is evident that this result is achieved by partially bending the contact arms,
subsequent bending of the connecting web, final shaping of the arms and finally final bending of the connecting web.

Wk An additional advantage of the method described above is that the tips 24 of the contact arms 20, which are opposite the heat sink 4, are provided with solder. These arms are formed from the portion of the metal strip provided with a solder strip and bent to achieve this effect during the forming.

Claims i

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Claims (6)

2U3809 Claims Γΐ / A method for producing lead frames in the form of a continuous strip, characterized in that a metal strip (30) is punched out so that a sequence of frame blanks lying next to one another is formed, each blank having a heat sink (4) and three spaced apart has parallel supply lines (6, 8, 10) which extend transversely with respect to the longitudinal axis of the metal strip (30), the middle (8) of the supply lines having an edge (l4) of the heat sink (4) via a connecting web ( 12 ¹ ) and the outer leads (6, 10) each have a contact arm (20 ') at one end (18) adjacent to the heat sink (4) and the contact arms (20 ¹ ) extend along the length of the metal strip in opposite directions and the supply lines (6, 8, 10) are connected to one another by means of a connection web (l6) formed in one piece therewith, that the arms (20 ¹ ) are bent laterally to the plane of the metal strip (30), that the connecting part (12 *) is bent at a point (I3) away from the edge of the heat sink (4) so that the leads (6, 8, 10) are pivoted in a curved path and in a transverse to the plane of the metal strip (30) extending plane, the arms (20 ') being arranged on one side of the heat sink (4) and the free ends of the supply lines (6, 8, 10) being arranged on the opposite side , that the arms are shaped (20 x) is essentially in its final configuration,
and that the connecting part (12 ·) at a point (15) in dee near edge (L4) of the heat sink (4) is bent so that the leads (6, 8, 10) pivoted along a curved path and are oriented in a plane which in the waste , stood and parallel to the plane of the metal strip (30) 209811/1254 runs, the arms (20 ¹ ) are positioned between said planes. ',, 2. The method according to claim 1, characterized in that that the arms (20 ') initially partially be turned towards each other. 3. The method according to claim 2, characterized in that during the further shaping the arms (20 ') are bent inwardly until their ends (24) are spaced apart from one another which is less than the width of the connecting part (12 ¹ ) . 4. The method according to any one of claims 1 to 3, characterized in that the connecting part (12 *) is further shaped by being bent at both points (13 and 15) until the connecting part (12 ¹ ) is substantially parallel to and between the plane in which the leads (6, 8, 10) lie and the plane of the metal strip (30). 5 · Method according to one of Claims 1 to 4, characterized in that the metal strip (30) had a relatively large cross-section Section (3.2) and a section (34) which is relatively thin in cross section, that the heat sink (4) from the thick section (32) and the leads (6, 8, 10) are formed from the thin section (34) 6. The method according to claim 5, characterized in that a solder strip (26 ') is provided on the metal strip (30), so that at least part of the heat sink (4) and the contact arms (20 ¹ ) has a surface covered with solder. 209811/1254 BAD ORiQfNAL