Soldering on thin glass sheets

Abstract

A process is disclosed, whereby soldered connections to electrical conductors incorporated on thin glass are achieved. Sufficient resistance to cracking is obtained by virtue of surface stresses induced locally in a region where soldering is to be done. In a preferred embodiment, surface stresses imparted during a press bending operation are relied upon.

Claims

1. A laminated glazing comprising: a first glass sheet having a thickness of less than 2.1 mm and a center part; a first electrical conductor formed as a layer of conductive metallic ink printed on said first glass sheet; a second electrical conductor connected to said first electrical conductor by a soldered connection at a soldering region of the first glass sheet, said soldering region of the first glass sheet being closer than the center part of the first glass sheet to an edge of the first glass sheet, said soldering region having a surface stress that is locally increased, prior to soldering of the soldered connection, to be higher than a surface stress in the center part; a second glass sheet; and a polymer interlayer disposed between the first and second glass sheets, the first glass sheet and the second glass sheet being bonded together by said interlayer; wherein an opaque coating applied around a periphery of said first glass sheet, said coating applied around the periphery of said first glass sheet including a gap between portions of the opaque coating where the surface of the first glass sheet is not applied with the opaque coating and where said first electrical conductor is printed, the opaque coating being out of contact with the first electrical conductor; wherein a second opaque coating placed between the polymer interlayer and the second glass sheet overlapping the first electrical conductor placed within the gap.

2. The laminated glazing according to claim 1, where the first glass sheet has a surface stress between 8 MPa and 25 MPa.

3. The laminated glazing according to claim 2, where the first glass sheet has a surface stress between 8 MPa and 20 MPa.

4. The laminated glazing according to claim 3, where the first glass sheet has a surface stress between 8 MPa and 15 MPa.

5. The laminated glazing according to claim 1, where the first glass sheet has a thickness of less than or equal to 1.6 mm.

6. The laminated glazing according to claim 5, where the first glass sheet has a thickness of less than or equal to 1 mm.

7. The laminated glazing according to claim 1, wherein the first electrical conductor is disposed between the first glass sheet and the second electrical conductor.

8. The laminated glazing according to claim 1, wherein the conductive metallic ink is a silver ink.

Description

(1) The invention will now be described by non-limiting example, with reference to the following figures in which:

(2) FIG. 1 illustrates the positions on vehicle glazings at which surface stress measurements were made, in order to assess the effect on surface stress of a typical press bending process;

(3) FIG. 2 illustrates a typical laminated glazing assembly according to the invention and

(4) FIG. 3 shows the positions of soldered connections that were arranged on glazing laminates according to the invention for subsequent evaluation.

(5) Table 1 shows measured surface stress values obtained on a total of 15 samples of glass sheets following processing according to Pilkington Group advanced press bending process.

(6) The measurements were done using a GASP surface stress meter on the outer surface (surface 1) of the non laminated pair of glass.

(7) Each pair of glasses was taped to avoid sliding during measurement and was positioned on an airbag for measuring. The positions for surface stress measurement were selected according to positions used in a former stone impact test (S/TN2001/02) and are labelled T.sub.1-T.sub.3 and B.sub.1-B.sub.3 in FIG. 1 (dimensions are in mm).

(8) At each position stress measurements were done perpendicular (p) and parallel (n) to bottom edge.

(9) The data presented in table 1 shows that surface stress in the glass samples wore typically in the range from 12 to 15 MPa although values as low as about 8 MPa and as high as 18.4 MPa are recorded.

(10) The inventors have also observed that semi-toughened glass having a surface stress of about 20 MPa to 25 MPa performs as well as fully toughened glass in terms of the reliability of soldered connections to circuits printed on the glass.

(11) TABLE-US-00001 TABLE 1 Surface stress in MPa (all stresses are compressive surface stresses on outer glass) Sample No. measurement 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Position Thickness (outer/inner) on glass direction 2.1 gr/1.6 cl 1.8 cl/1.8 cl 2.1 gr/2.1 cl 2.1 gr/1.8 cl 1.8 gr/1.8 gr T1 n 15.1 15.8 17.8 14.9 14.5 12.8 14.4 14.9 14.2 17.0 14.4 14.5 14.2 13.3 11.7 p 18.4 13.7 16.2 11.2 11.6 11.7 14.2 13.5 13.7 15.4 16.2 14.2 13.7 12.4 10.6 T2 n 15.1 16.4 17.6 13.5 12.8 13.2 14.7 15.8 15.3 14.0 14.7 15.6 13.2 12.3 12.5 p 15.3 15.3 12.5 11.9 9.6 9.9 14.0 14.9 16.2 13.8 13.0 14.0 12.0 12.3 11.4 T3 n 16.6 15.3 17.4 12.5 13.5 14.4 15.3 14.2 14.4 16.6 13.8 13.1 13.8 13.2 13.5 p 17.8 13.7 13.3 11.6 12.7 13.3 15.8 14.2 13.8 15.3 12.8 14.9 12.3 13.0 11.7 B1 n 14.9 16.2 15.9 11.6 13.7 12.0 13.2 15.4 15.3 13.0 16.6 17.0 13.3 14.5 12.2 p 14.5 16.4 14.0 10.5 11.1 10.1 14.0 13.7 12.8 13.7 12.7 16.0 11.9 12.3 11.2 B2 n 13.7 13.8 17.4 12.0 13.3 12.5 14.4 15.1 14.5 14.2 15.8 16.7 12.8 12.8 13.0 p 15.2 13.2 13.0 9.2 10.3 9.3 13.0 14.0 14.9 14.9 14.7 14.5 12.2 10.0 11.1 B3 n 14.5 15.1 17.2 14.2 14.2 12.7 16.2 17.6 15.2 14.5 16.2 17.8 13.7 14.0 12.2 p 16.6 16.0 14.9 9.6 10.5 8.6 14.2 13.8 11.9 14.4 13.2 15.5 11.1 11.6 10.6 Meanings: nstress parallel to bottom edge pstress perpendicular to bottom edge cl = clear glass gr = green glass

(12) A number of tests were performed to assess the performance of soldered connections to electrical circuits on thin glass subjected to Pilkington's Advanced Press Bending process.

(13) For many years, a standard thermal cycling test has been used to evaluate the performance of soldered connections on vehicle glazings. Experience indicates that products showing a failure rate of up to 30% in this test give acceptable performance in service.

(14) Silver ink patches were printed manually on to samples for asymmetric production windscreens (2.1 mm/1.6 mm). For some samples printing was done directly on the glass and on others, printing was done on the black printed area for soldering contacts.

(15) After the standard furnace process and lamination three different type of connectors for heater applications were appliedbraid, stranded wire and stranded wire with a flattened wire end sleeve.

(16) Soldered samples were then aged in a thermal cycling test acc. DBL 5610 with increased speed for temperature change (16 h @40 C.; 60 min slope up; 8 h@+80 C.; 90 min slope down) and inspected again after test.

(17) Finally pull off tests were done on all connectors.

(18) 180 connectors on silver and 180 connectors on silver/black were evaluated. The results are shown in tables 2a and 2b.

(19) TABLE-US-00002 TABLE 2a Test results for Standard Soldering on Silver Patches on 1.6 mm APBL Glass. Fracture Mean value of failure 12 connectors Windscreen After thermal Pull Off No Connector cycle (%) Forces [N] 1 Wire 8 102 2 Wire 33 77 3 Wire 50 59 4 Wire 17 64 5 Wire 17 56 1 Wire-Plate 8 148 2 Wire-Plate 8 143 3 Wire-Plate 0 133 4 Wire-Plate 0 116 5 Wire-Plate 0 131 1 Braid 25 119 2 Braid 17 104 3 Braid 17 97 4 Braid 17 80 5 Braid 8 92

(20) TABLE-US-00003 TABLE 2b Test results for Standard Soldering on Silver Patches over Blackprint on 1.6 mm APBL Glass. Fracture Mean value of failure 12 connectors Windscreen After thermal Pull Off No Connector cycle (%) Forces [N] 1 Wire 100 Pull off forces not tested 2 Wire 100 Pull off forces not tested 3 Wire 100 Pull off forces not tested 4 Wire 100 Pull off forces not tested 5 Wire 100 Pull off forces not tested 1 Wire-Plate 8 Pull off forces not tested 2 Wire-Plate 42 Pull off forces not tested 3 Wire-Plate 67 Pull off forces not tested 4 Wire-Plate 58 Pull off forces not tested 5 Wire-Plate 50 Pull off forces not tested 1 Braid 100 Pull off forces not tested 2 Braid 100 Pull off forces not tested 3 Braid 100 Pull off forces not tested 4 Braid 100 Pull off forces not tested 5 Braid 92 Pull off forces not tested

(21) Referring to tables 2a and 2b, twelve samples for each of three connector types on each of five windscreens were tested both on silver on glass patches (table 2a) and on silver over black print (table 2b). Inspection for fracture failure was done on each sample immediately after soldering and in no case was any observed. Inspection was repeated after thermal cycling tests and results are shown. The result shows clearly that soldering on silver/black has a very high crack rate after thermal cycling with most connectors failing the test. For that reason, no further pull off tests were performed on these samples.

(22) However, the results obtained from silver conductive ink printed directly on glass were very different: no failure after soldering was seen and only 15% failure was noted after thermal cycling. For the stranded wire with flattened wire end sleeve the failure rate was even lower (only 2 failures or 3% on 60 tested connectors).

(23) Moreover, the ink directly on glass samples performed well in the pull off test. A mean value of 134N for the stranded wire with flattened sleeve gives good confidence for the performance against a minimum required pull off force of 40N. The pull-off failure mode in each case was silver/glass.

(24) Referring to FIG. 2, a laminated glazing according to the invention comprises inner and outer glass sheets 1 and 2 respectively having a thickness of less than 2.1 mm. Inner sheet has a surface stress of greater than 8 MPa but less than 25 MPa.

(25) An interlayer 3 of polymer material such as PVB is disposed between the glass sheets 1 and 2 an obscuration bands is provided by printed ceramic ink layers 4, 5 on the inner surfaces of sheets 1 and 2. Ink layers 4, 5 are formed by screen printing and subsequent firing in a process that is well known to a person skilled in the art and needs no further explanation here.

(26) In order to facilitate printing of an electrical conductor 6 in conductive ink such as silver based ink directly on to the inner surface of glass sheet 1, ink layer 4 includes a gap where the substrate glass sheet 1 is exposed. Such a gap is easily realised in the screen printing process.

(27) Electrical conductor 6 may then be printed directly on sheet 1 thus facilitating a more reliable solder connection 7 to a second conductor 8 as explained previously. Electrical conductor 6 could be, for example, a wiper rest area heating element or a busbar and remains hidden from view to a person outside of the vehicle by virtue of layer 5. Conductor 8 typically leads to other equipment such as a power supply or radio receiver.

(28) As previously noted, existing technology allows for differential heating of one or both dies in the apparatus used for press bending. In a preferred embodiment of the invention, such facilities are used to induce greater local surface stress in a region of the glass sheet where soldering is done.

(29) Referring to FIG. 3, a further set of 12 laminated glass samples were prepared from glass sheets that were subjected to Pilkington's APBL process and a polyvinyl butyral interlayer. A black ceramic ink (obscuration band) and silver ink layer was applied and test solder connections were made at each of positions 9-16 (T-piece connectors) and A-E (radio button connectors).

(30) The samples were then aged in a thermal cycling test acc. DBL 5610 with increased speed for temperature change (16 h@40 C.; 60 min slope up; 8 h@+80 C.; 90 min slope down). Inspection before and after test showed no cracking.

(31) The samples were then subjected to humidity testing which involved exposure to 95% humidity at 50 C. for over 240 hours before pull off forces were ascertained.

(32) Table 3 indicates the results of this procedure. Two target surface stress levels, namely 20 MPa and 35 MPa, were chosen for the samples. The actual surface stress levels were measured at points approximately indicated by X in FIG. 3 and ranged from 18-22 MPa and 33-37 MPa.

(33) Mean pull off forces were determined and are shown in the table (maximum force applied was 200N).

(34) TABLE-US-00004 TABLE 3 Test results for Standard Soldering on Silver Print over Blackprint on laminates formed from APBL Glass. Mean Mean Pull ull off off Silver- Stress force force Failure- No. Thickness Ink Black-Ink Level (1-8) (A-E) Mode 1 1.6/1.6 mm 1903 F- 20 126 200 glass 14510IR 2 1.6/1.6 mm 1903 F- 35 111 200 glass 14510IR 3 1.6/1.6 mm 1903 JM- 20 97 198 glass 1730IR 4 1.6/1.6 mm 1903 JM- 35 136 200 glass 1730IR 5 1.8/1.8 mm 1903 F- 20 116 200 glass 14510IR 6 1.8/1.8 mm 1903 F- 35 180 195 glass 14510IR 7 1.8/1.8 mm 1903 JM- 20 104 189 glass 1730IR 8 1.8/1.8 mm 1903 JM- 35 153 200 glass 1730IR 9 2.1/2.1 mm 1903 F- 20 178 185 glass 14510IR 10 2.1/2.1 mm 1903 F- 35 124 200 glass 14510IR 11 2.1/2.1 mm 1903 JM- 20 189 174 glass 1730IR 12 2.1/2.1 mm 1903 JM- 35 193 189 glass 1730IR

(35) The samples were examined for cracking after the humidity testing and none was detected.