Abstract:
A method of depositing encapsulant on a line of wire bonds to a die is described, the die having a back surface in contact with the support structure and an active surface opposing the back surface, the active surface having electrical contact pads and functional elements spaced from the contact pads. The method involves the steps of providing a die mounted to the support structure, positioning a barrier between the contact pads and the functional elements, the barrier being proximate to, but spaced from the active surface, depositing a bead of encapsulant onto the electrical contact pads while the barrier remains stationary such that the barrier prevents the encapsulant from contacting the functional elements, removing the barrier when the bead of encapsulant has been deposited. The fluidic resistance generated by the gap between the barrier and the active surface means that the amount of encapsulant that flows into the gap and onto the active surface is almost constant. The reduced flow variations make the encapsulant front closely correspond to the shape of the barrier. Greater control of the encapsulant front allows the functional elements of the active surface of the die to be closer to the contact pads.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 11/860,541 filed Sep. 25, 2007 all of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of integrated circuit packaging. In particular, the encapsulation of the wire bonds between a circuit board and the contact pads on the integrated circuit die. 
     CO-PENDING APPLICATIONS 
     The following applications have been filed by the Applicant with the present application: 
     
         
         Ser. No. 11/860,538 
         Ser. No. 11/860,539 
         Ser. No. 11/860,540 
         U.S. Pat. No. 7,618,842
 
The disclosures of these co-pending applications are incorporated herein by reference.
 
       
    
     CROSS REFERENCES TO RELATED APPLICATIONS 
     Various methods, systems and apparatus relating to the present invention are disclosed in the following U.S. patents/patent applications filed by the applicant or assignee of the present invention: 
                                                 6,405,055   6,628,430   7,136,186   7,286,260   7,145,689       7,130,075   7,081,974   7,177,055   7,209,257   7,161,715       7,154,632   7,158,258   7,148,993   7,075,684   7,158,809       7,430,067   7,431,519   7,460,882   7,564,580   11/650,545       11/653,241   7,241,005   7,108,437   6,915,140   6,999,206       7,136,198   7,092,130   7,249,108   6,566,858   6,331,946       6,246,970   6,442,525   7,346,586   09/505,951   6,374,354       7,246,098   6,816,968   6,757,832   6,334,190   6,745,331       7,249,109   7,197,642   7,093,139   7,509,292   10/636,283       10/866,608   7,210,038   7,401,223   10/940,653   10/942,858       11/706,329   11/757,385   7,657,488   7,170,652   6,967,750       6,995,876   7,099,051   7,453,586   7,193,734   11/209,711       7,468,810   7,095,533   6,914,686   7,161,709   7,099,033       7,364,256   7,258,417   7,293,853   7,328,968   7,270,395       7,461,916   7,510,264   7,334,864   7,255,419   7,284,819       7,229,148   7,258,416   7,273,263   7,270,393   6,984,017       7,347,526   7,357,477   11748482   7,562,960   11/779,851       7,524,017   11/853,816   11/853,814   11/853,786   11/856,694       7,465,015   7,364,255   7,357,476   11/003,614   7,284,820       7,341,328   7,246,875   7,322,669   11/764,760   11/853,777       7,445,311   7,452,052   7,455,383   7,448,724   7,441,864       7,637,588   7,648,222   11/482,968   7,607,755   11/482,971       7,658,463   7,344,226   7,328,976   11/685,084   11/685,086       11/685,090   11/740,925   7,605,009   7,568,787   11/518,238       11/518,280   11/518,244   11/518,243   11/518,242   7,331,651       7,334,870   7,334,875   7,416,283   7,438,386   7,461,921       7,506,958   7,472,981   7,448,722   7,438,381   7,441,863       7,438,382   7,425,051   7,399,057   11/246,671   11/246,670       11/246,669   7,448,720   7,448,723   7,445,310   7,399,054       7,425,049   7,367,648   7,370,936   7,401,886   7,506,952       7,401,887   7,384,119   7,401,888   7,387,358   7,413,281       7,530,663   7,467,846   11/482,962   11/482,963   11/482,956       11/482,954   11/482,974   7,604,334   11/482,987   11/482,959       11/482,960   11/482,961   11/482,964   11/482,965   7,510,261       11/482,973   7,581,812   7,641,304   11/495,817   6,227,652       6,213,588   6,213,589   6,231,163   6,247,795   6,394,581       6,244,691   6,257,704   6,416,168   6,220,694   6,257,705       6,247,794   6,234,610   6,247,793   6,264,306   6,241,342       6,247,792   6,264,307   6,254,220   6,234,611   6,302,528       6,283,582   6,239,821   6,338,547   6,247,796   6,557,977       6,390,603   6,362,843   6,293,653   6,312,107   6,227,653       6,234,609   6,238,040   6,188,415   6,227,654   6,209,989       6,247,791   6,336,710   6,217,153   6,416,167   6,243,113       6,283,581   6,247,790   6,260,953   6,267,469   6,588,882       6,742,873   6,918,655   6,547,371   6,938,989   6,598,964       6,923,526   6,273,544   6,309,048   6,420,196   6,443,558       6,439,689   6,378,989   6,848,181   6,634,735   6,299,289       6,299,290   6,425,654   6,902,255   6,623,101   6,406,129       6,505,916   6,457,809   6,550,895   6,457,812   7,152,962       6,428,133   7,216,956   7,080,895   7,442,317   7,182,437       7,357,485   7,387,368   11/607,976   7,618,124   7,654,641       11/607,980   7,611,225   11/607,978   11/735,961   11/685,074       7,637,582   7,419,247   7,384,131   11/763,446   7,416,280       7,252,366   7,488,051   7,360,865   11766713   7,631,956       11/482,980   11/563,684   11/482,967   11/482,966   11/482,988       11/482,989   7,438,371   7,465,017   7,441,862   7,654,636       7,458,659   7,455,376   11/124,158   11/124,196   11/124,199       11/124,162   11/124,202   11/124,197   11/124,198   7,284,921       11/124,151   7,407,257   7,470,019   7,645,022   7,392,950       11/124,149   7,360,880   7,517,046   7,236,271   11/124,174       11/124,194   11/124,164   7,465,047   7,607,774   11/124,166       11/124,150   11/124,172   11/124,165   7,566,182   11/124,185       11/124,184   11/124,182   11/124,201   11/124,171   11/124,181       11/124,161   7,595,904   11/124,191   11/124,159   7,466,993       7,370,932   7,404,616   11/124,187   11/124,189   11/124,190       7,500,268   7,558,962   7,447,908   11/124,178   11/124,177       7,456,994   7,431,449   7,466,444   11/124,179   11/124,169       11/187,976   11/188,011   7,562,973   7,530,446   7,628,467       7,572,077   11/228,540   11/228,500   11/228,501   11/228,530       11/228,490   11/228,531   11/228,504   11/228,533   11/228,502       11/228,507   11/228,482   11/228,505   7,641,115   11/228,487       7,654,444   11/228,484   7,499,765   11/228,518   11/228,536       11/228,496   7,558,563   11/228,506   11/228,516   11/228,526       11/228,539   11/228,538   11/228,524   11/228,523   7,506,802       11/228,528   11/228,527   7,403,797   11/228,520   7,646,503       11/228,511   11/228,522   11/228,515   11/228,537   11/228,534       11/228,491   11/228,499   11/228,509   11/228,492   7,558,599       11/228,510   11/228,508   11/228,512   11/228,514   11/228,494       7,438,215   11/228,486   7,621,442   7,575,172   7,357,311       7,380,709   7,428,986   7,403,796   7,407,092   11/228,513       7,637,424   7,469,829   11/228,535   7,558,597   7,558,598       6,087,638   6,340,222   6,041,600   6,299,300   6,067,797       6,286,935   6,044,646   6,382,769   6,787,051   6,938,990       7,588,693   7,416,282   7,481,943   11/766,052   7,152,972       7,513,615   6,746,105   11/763,440   11/763,442   11/246,687       7,645,026   7,322,681   11/246,686   11/246,703   11/246,691       7,510,267   7,465,041   11/246,712   7,465,032   7,401,890       7,401,910   7,470,010   11/246,702   7,431,432   7,465,037       7,445,317   7,549,735   7,597,425   11/246,674   11/246,667       11/829,957   11/829,960   11/829,961   11/829,962   11/829,963       11/829,966   11/829,967   11/829,968   11/829,969   7,156,508       7,159,972   7,083,271   7,165,834   7,080,894   7,201,469       7,090,336   7,156,489   7,413,283   7,438,385   7,083,257       7,258,422   7,255,423   7,219,980   7,591,533   7,416,274       7,367,649   7,118,192   7,618,121   7,322,672   7,077,505       7,198,354   7,077,504   7,614,724   7,198,355   7,401,894       7,322,676   7,152,959   7,213,906   7,178,901   7,222,938       7,108,353   7,104,629   7,455,392   7,370,939   7,429,095       7,404,621   7,261,401   7,461,919   7,438,388   7,328,972       7,322,673   7,306,324   7,306,325   7,524,021   7,399,071       7,556,360   7,303,261   7,568,786   7,517,049   7,549,727       7,399,053   11/737,080   7,467,849   7,556,349   7,648,226       11/782,593   7,303,930   7,401,405   7,464,466   7,464,465       7,246,886   7,128,400   7,108,355   6,991,322   7,287,836       7,118,197   7,575,298   7,364,269   7,077,493   6,962,402       10/728,803   7,147,308   7,524,034   7,118,198   7,168,790       7,172,270   7,229,155   6,830,318   7,195,342   7,175,261       7,465,035   7,108,356   7,118,202   7,510,269   7,134,744       7,510,270   7,134,743   7,182,439   7,210,768   7,465,036       7,134,745   7,156,484   7,118,201   7,111,926   7,431,433       7,018,021   7,401,901   7,468,139   7,128,402   7,387,369       7,484,832   11/490,041   7,506,968   7,284,839   7,246,885       7,229,156   7,533,970   7,467,855   7,293,858   7,520,594       7,588,321   7,258,427   7,556,350   7,278,716   11/603,825       7,524,028   7,467,856   7,469,996   7,506,963   7,533,968       7,556,354   7,524,030   7,581,822   7,533,964   7,549,729       11/842,950   7,543,916   11/097,308   7,448,729   7,246,876       7,431,431   7,419,249   7,377,623   7,328,978   7,334,876       7,147,306   7,261,394   7,611,218   7,637,593   7,654,645       11/482,977   7,491,911   11/764,808   09/575,197   7,079,712       6,825,945   7,330,974   6,813,039   6,987,506   7,038,797       6,980,318   6,816,274   7,102,772   7,350,236   6,681,045       6,728,000   7,173,722   7,088,459   09/575,181   7,068,382       7,062,651   6,789,194   6,789,191   6,644,642   6,502,614       6,622,999   6,669,385   6,549,935   6,987,573   6,727,996       6,591,884   6,439,706   6,760,119   7,295,332   6,290,349       6,428,155   6,785,016   6,870,966   6,822,639   6,737,591       7,055,739   7,233,320   6,830,196   6,832,717   6,957,768       7,456,820   7,170,499   7,106,888   7,123,239   7,468,284       7,341,330   7,372,145   7,425,052   7,287,831   10/727,181       10/727,162   7,377,608   7,399,043   7,121,639   7,165,824       7,152,942   10/727,157   7,181,572   7,096,137   7,302,592       7,278,034   7,188,282   7,592,829   10/727,180   10/727,179       10/727,192   10/727,274   10/727,164   7,523,111   7,573,301       7,660,998   10/754,536   10/754,938   10/727,160   7,171,323       7,278,697   7,360,131   7,519,772   7,328,115   11/749,750       11/749,749   7,369,270   6,795,215   7,070,098   7,154,638       6,805,419   6,859,289   6,977,751   6,398,332   6,394,573       6,622,923   6,747,760   6,921,144   10/884,881   7,092,112       7,192,106   7,457,001   7,173,739   6,986,560   7,008,033       7,551,324   7,222,780   7,270,391   7,525,677   7,388,689       7,398,916   7,571,906   7,654,628   7,611,220   7,556,353       7,195,328   7,182,422   11/650,537   11/712,540   7,374,266       7,427,117   7,448,707   7,281,330   10/854,503   7,328,956       10/854,509   7,188,928   7,093,989   7,377,609   7,600,843       10/854,498   10/854,511   7,390,071   10/854,525   10/854,526       7,549,715   7,252,353   7,607,757   7,267,417   10/854,505       7,517,036   7,275,805   7,314,261   7,281,777   7,290,852       7,484,831   10/854,523   10/854,527   7,549,718   10/854,520       7,631,190   7,557,941   10/854,499   10/854,501   7,266,661       7,243,193   10/854,518   10/934,628   7,163,345   7,322,666       7,566,111   7,434,910   11/735,881   11/748,483   11/749,123       11/766,061   7,465,016   11/772,235   11/778,569   7,467,836       7,543,808   11/544,764   11/544,765   11/544,772   11/544,774       11/544,775   7,425,048   11/544,766   11/544,767   7,384,128       7,604,321   11/544,769   11/544,777   7,425,047   7,413,288       7,465,033   7,452,055   7,470,002   11/293,833   7,475,963       7,448,735   7,465,042   7,448,739   7,438,399   11/293,794       7,467,853   7,461,922   7,465,020   11/293,830   7,461,910       11/293,828   7,270,494   7,632,032   7,475,961   7,547,088       7,611,239   11/293,819   11/293,818   11/293,817   11/293,816       11/838,875   11/482,978   11/640,356   11/640,357   11/640,358       11/640,359   11/640,360   11/640,355   11/679,786   7,448,734       7,425,050   7,364,263   7,201,468   7,360,868   7,234,802       7,303,255   7,287,846   7,156,511   10/760,264   7,258,432       7,097,291   7,645,025   10/760,248   7,083,273   7,367,647       7,374,355   7,441,880   7,547,092   10/760,206   7,513,598       10/760,270   7,198,352   7,364,264   7,303,251   7,201,470       7,121,655   7,293,861   7,232,208   7,328,985   7,344,232       7,083,272   7,311,387   7,303,258   11/706,322   7,517,050       11/749,119   11/779,848   11/855,152   11/855,151   7,621,620       11/014,763   7,331,663   7,360,861   7,328,973   7,427,121       7,407,262   7,303,252   7,249,822   7,537,309   7,311,382       7,360,860   7,364,257   7,390,075   7,350,896   7,429,096       7,384,135   7,331,660   7,416,287   7,488,052   7,322,684       7,322,685   7,311,381   7,270,405   7,303,268   7,470,007       7,399,072   7,393,076   11/014,750   7,588,301   7,249,833       7,547,098   11/775,143   7,467,860   7,524,016   7,490,927       7,331,661   7,524,043   7,300,140   7,357,492   7,357,493       7,566,106   7,380,902   7,284,816   7,284,845   7,255,430       7,390,080   7,328,984   7,350,913   7,322,671   7,380,910       7,431,424   7,470,006   7,585,054   7,347,534   7,441,865       7,469,989   7,367,650   11/778,567   11852958   11/852,907       7,469,990   7,441,882   7,556,364   7,357,496   7,467,863       7,431,440   7,431,443   7,527,353   7,524,023   7,513,603       7,467,852   7,465,045   11/688,863   11/688,864   7,475,976       7,364,265   11/688,867   11/688,868   11/688,869   11/688,871       11/688,872   7,654,640   11/741,766   7,645,034   7,637,602       7,645,033   11/495,818   11/495,819   11/677,049   11/677,050       7,658,482   7,306,320   7,111,935   7,562,971   10/760,219       7,604,322   7,261,482   10/760,220   7,002,664   10/760,252       7,088,420   11/446,233   7,470,014   7,470,020   7,540,601       7,654,761   7,377,635   11/014,727   7,237,888   7,168,654       7,201,272   6,991,098   7,217,051   6,944,970   10/760,215       7,108,434   7,210,407   7,186,042   10/760,266   6,920,704       7,217,049   7,607,756   10/760,260   7,147,102   7,287,828       7,249,838   10/760,241   7,431,446   7,611,237   7,261,477       7,225,739   10/962,402   10/962,425   7,419,053   7,191,978       10/962,426   7,524,046   10/962,417   10/962,403   7,163,287       7,258,415   7,322,677   7,258,424   7,484,841   7,195,412       7,207,670   7,270,401   7,220,072   7,588,381   11/544,547       11/585,925   7,578,387   11/706,298   7,575,316   7,384,206       7,628,557   7,470,074   7,425,063   7,429,104   7,556,446       7,367,267   11/754,359   11/778,061   11/765,398   11/778,556       7,448,551   7,399,065   11/223,262   11/223,018   7,322,761       11/223,021   11/223,020   11/014,730   7,154,626   7,079,292       11/604,316                    
The disclosures of these co-pending applications are incorporated herein by reference.
 
     BACKGROUND OF THE INVENTION 
     Integrated circuits fabricated on silicon wafer substrates are electrically connected to printed circuit boards by wire bonds. The wire bonds are very thin wires—around 25 to 40 microns in diameter—extending from contact pads along the side of the wafer substrate to contacts on the printed circuit board (PCB). To protect and strengthen the wire bonds, they are sealed within a bead of epoxy called encapsulant. The wires from the contact pads to the PCB are made longer than necessary to accommodate changes in the gap between the PCB and the contact pads because of thermal expansion, flex in the components and so on. These longer than necessary wires naturally form an arc between the contact pads and the PCB. The top of the wire arc is often about 300 microns above the contact pads although some wire bonding may extend even higher. As the name suggests, the encapsulant needs to encapsulate the full length of the wire so the encapsulant bead will extend 500 microns to 600 microns proud of the contact pads. 
     The integrated circuit fabricated on the silicon wafer is often referred to as a ‘die’. For the purposes of this specification, the term die will be used as a reference to an integrated circuit fabricated on a wafer substrate using lithographic the well known etching and deposition techniques commonly used in semiconductor fabrication. If the die is purely an electronic microprocessor, there is little need to keep close control of the encapsulant bead dimensions. However, if the die is a micro-electro mechanical systems (MEMS) device with an active upper surface, it may be necessary or desirable to bring the active surface of the die onto close proximity with another surface. One such situation applies to inkjet printheads. The proximity of the print media to the nozzle array influences the print quality. Similarly, if a cleaning surface is wiped across the nozzles, the bead of encapsulant can hamper the wiping contact. 
     Another problems arises because of sides of the encapsulant bead are not straight. One commonly used technique for depositing the encapsulant involves extruding it from a needle directly onto the line of wire bonds. The encapsulant volume and placement on the die is not very accurate. Variations in the pressure from the pump or slight non-uniformities in the speed of the needle cause the side of the bead contacting the active surface to be reasonably crooked. As the side of the bead is not straight, it has to be generously spaced from any active parts on the active surface to comfortably accommodate the perturbations. Spacing the electrical contacts away from the active portions (say for example, inkjet nozzles) of the active surface uses up valuable wafer real estate and reduces the number of dies that can be fabricated from a wafer disc. 
     In light of the widespread use of inkjet printheads, the invention will be described with specific reference to its application in this field. However, the ordinary will appreciate that this is purely illustrative and the invention is equally applicable to other integrated circuits wire bonded to a PCB or other support structure. 
     SUMMARY OF THE INVENTION 
     According to a first aspect, the present invention provides a microprocessor device comprising: 
     a support structure having a chip mounting area and a conductor mounting area; 
     a die supported on the chip mounting area, the die having a back surface in contact with the chip mounting area and an active surface opposing the back surface, the active surface having electrical contact pads; 
     a plurality of electrical conductors at least partially supported on the conductor mounting area; and, 
     a series of wire bonds extending from the electrical contact pads to the plurality of electrical conductors supported on the conductor mounting area; wherein, 
     the chip mounting area is raised relative to the conductor mounting area. 
     By raising the chip mounting area relative to the rest of the PCB, or at least the conductors connected to the PCB end of the wire bonds, the top of the arc formed by the layer is much closer to the active surface of the die. This, in turn, allows the bead of encapsulant to have a lower profile relative to the active surface. With a lower encapsulant bead, the active surface can be brought into closer proximity with another surface without making contact. For example, the nozzle array on a printhead IC can be 300 microns to 400 microns from the paper path. 
     Preferably, the chip mounting area is raised more than 100 microns relative to the conductor mounting area. Preferably, the support structure has a step between the chip mounting area and the conductor mounting area. 
     Preferably, the plurality of conductors are incorporated into a flexible printed circuit board (flex PCB) with a line of bond pads along an edge closest the die, the bond pads being more than 2 mm from the contacts pads on the die. 
     Preferably, the wire bonds are formed from wire with a diameter less than 40 microns and extend less than 100 microns above the active surface of the die. 
     Preferably, the wire bonds are plastically deformed such that they extend less than 50 microns above the active surface of the die. 
     Preferably, the active surface has functional elements spaced less than 260 microns from the contacts pads of the die. In a particularly preferred form, the die is an inkjet printhead IC and the functional elements are nozzles through which ink is ejected. In some embodiments, the support structure is a liquid crystal polymer (LCP) molding. 
     Preferably, the wire bonds are covered in a bead of encapsulant, the bead of encapsulant extending less than 200 microns above the active surface of the die. 
     Preferably, the wire bonds are covered in a bead of encapsulant, the bead of encapsulant having a profiled surface that is flat, parallel to and spaced less than 100 microns from the active surface. 
     Preferably, the wire bonds are covered in a bead of encapsulant, the bead of encapsulant having a profiled surface that is flat and inclined relative to the active surface. 
     Preferably, the wire bonds are covered in a bead of encapsulant, the encapsulant being an epoxy material that is thixotropic when uncured. 
     Preferably, the wire bonds are covered in a bead of encapsulant, the encapsulant being an epoxy material has a viscosity greater than 700 cp when uncured. 
     In a particular embodiment, the printhead IC is mounted in a printer such that during use the nozzles are less than 100 microns from the paper path. 
     According to a second aspect, the present invention provides a method of profiling a wire bond between a contact pad on a die, and a conductor on a supporting structure, the method comprising the steps of: 
     electrically connecting the contact pad on the die to the conductor on the supporting structure with a wire bond, the wire bond extending in an arc from the contact pad to the conductor; 
     pushing on the wire bond to collapse the arc and plastically deform the wire bond; and, 
     releasing the wire bonds such that the plastic deformation maintains the wire bond in a flatter profile shape. 
     The strength of the wire bond is known to be relatively small; of the order of 3 to 5 grams force. However, the Applicant&#39;s work has found that the wire bond structure is robust enough to withstand a certain degree of work hardening from plastic deformation. The arc of the wire bond can be deformed into a flatter profile without compromising the electrical connection with the PCB. 
     Preferably, the die has an active surface that has functional elements, the contacts pad being formed at one edge of the active surface, the wire bond has a diameter less than 40 microns and the arc extends more than 100 microns above the active surface of the die. 
     Preferably, the wire bond is plastically deformed such that it extends less than 50 microns above the active surface of the die. 
     Preferably, the wire bond is pushed by engagement with a blade having a rounded edge section for contacting the wire bond. 
     Preferably, the method further comprises the steps of: 
     applying a bead of encapsulant over the wire bond; and, 
     moving a profiling surface over the active surface to flatten the bead of encapsulant. 
     Preferably, the bead of encapsulant having a profiled surface that is flat, parallel to and spaced less than 100 microns from the active surface. 
     Optionally, the bead of encapsulant having a profiled surface that is flat and inclined relative to the active surface. 
     Preferably, the encapsulant being an epoxy material has a viscosity greater than 700 cp when uncured. In a particularly preferred form, the encapsulant being an epoxy material that is thixotropic when uncured. 
     Preferably, the method further comprises the steps of: 
     positioning the profiling surface adjacent and spaced from the active surface to define a gap; and, 
     applying the bead of encapsulant onto the contact pads such that one side of the bead contacts the profiling surface and a portion of the bead extends into the gap and onto the active surface. 
     Preferably, the active surface has functional elements spaced less than 260 microns from the contacts pads of the die. In a particularly preferred form, the die is an inkjet printhead IC and the functional elements are nozzles through which ink is ejected. In some embodiments, the printhead IC is mounted in a printer such that during use the nozzles are less than 100 microns from the paper path. 
     Preferably, the support structure has a chip mounting area and a conductor mounting area, the die is supported on the chip mounting area, and a plurality of electrical conductors at least partially supported on the conductor mounting area wherein, the chip mounting area is raised relative to the conductor mounting area. 
     Preferably, the chip mounting area is raised more than 100 microns relative to the conductor mounting area. Preferably, the support structure has a step between the chip mounting area and the conductor mounting area. In some embodiments, the plurality of conductors are incorporated into a flexible printed circuit board (flex PCB) with a line of bond pads along an edge closest the die, the bond pads being more than 2 mm from the contacts pads on the die. 
     Preferably, the support structure is a liquid crystal polymer (LCP) molding. 
     According to a third aspect, the present invention provides a method for profiling a bead of encapsulant extending along an edge of a die mounted to a supporting structure, the method comprising the steps of: 
     depositing a bead of encapsulant onto wire bonds along the edge of the die; 
     positioning a profiling surface over the die at a predetermined spacing from the die; 
     moving the profiling surface across the bead before the bead of encapsulant has cured to reshape the bead profile; and, 
     curing the bead of encapsulant. 
     The invention has found that the encapsulant can be effectively shaped by a profiling surface without stripping the encapsulant from the wire bonds. The normally convex-shaped upper surface of the encapsulant bead can be pushed to one side of the bead with the profiling surface. With a lower encapsulant bead, the active surface can be brought into closer proximity with another surface without making contact. For example, the nozzle array on a printhead IC can be 300 microns to 400 microns from the paper path. By collapsing or flattening the wire bond arcs before applying and profiling a bead of encapsulant, the nozzle array on the printhead IC can be less than 100 microns from the paper path. 
     Preferably, the wire bonds extend in an arc from respective contact pads on the die to corresponding conductors on the support structure and the method further comprises the steps of: 
     pushing on the wire bonds to plastically deform the wire bonds; and, 
     releasing the wire bond such that plastic deformation maintains the wire bond in a flatter profile shape. 
     Preferably, the die has an active surface that has functional elements, the contacts pad being formed at one edge of the active surface, the wire bond has a diameter less than 40 microns and the arc extends more than 100 microns above the active surface of the die. 
     Preferably, the wire bond is plastically deformed such that it extends less than 50 microns above the active surface of the die. 
     Preferably, the wire bond is pushed by engagement with a blade having a rounded edge section for contacting the wire bond. 
     Preferably, the bead of encapsulant has a profiled surface that is flat, parallel to and spaced less than 100 microns from the active surface. 
     Preferably, the bead of encapsulant has a profiled surface that is flat and inclined relative to the active surface. 
     Preferably, the encapsulant being an epoxy material has a viscosity greater than 700 cp when uncured. 
     Preferably, the encapsulant being an epoxy material that is thixotropic when uncured. 
     Preferably, the method further comprises the steps of: 
     positioning the profiling surface adjacent and spaced from the active surface to define a gap; and, 
     applying the bead of encapsulant onto the contact pads such that one side of the bead contacts the profiling surface and a portion of the bead extends into the gap and onto the active surface. 
     Preferably, the active surface has functional elements spaced less than 260 microns from the contacts pads of the die. In a further preferred form, the die is an inkjet printhead IC and the functional elements are nozzles through which ink is ejected. In some embodiments, the printhead IC is mounted in a printer such that during use the nozzles are less than 100 microns from the paper path. 
     Preferably, the support structure has a chip mounting area and a conductor mounting area, the die is supported on the chip mounting area, and a plurality of electrical conductors at least partially supported on the conductor mounting area wherein, the chip mounting area is raised relative to the conductor mounting area. 
     Preferably, the chip mounting area is raised more than 100 microns relative to the conductor mounting area. In a particularly preferred form, the support structure has a step between the chip mounting area and the conductor mounting area. 
     Preferably, the plurality of conductors are incorporated into a flexible printed circuit board (flex PCB) with a line of bond pads along an edge closest the die, the bond pads being more than 2 mm from the contacts pads on the die. 
     Preferably, the support structure is a liquid crystal polymer (LCP) molding. 
     According to a fourth aspect, the present invention provides a method of applying encapsulant to a die mounted to a support structure, the method comprising the steps of: 
     providing a die mounted to the support structure, the die having a back surface in contact with the support structure and an active surface opposing the back surface, the active surface having electrical contact pads; 
     positioning a barrier proximate the electrical contact pads and spaced from the active surface to define a gap; and, 
     depositing a bead of encapsulant onto the electrical contact pads such that one side of the bead contacts the barrier and a portion of the bead extends into the gap and onto the active surface. 
     Placing a barrier over the active surface so that it defines a narrow gap allows the geometry of the encapsulant front (the line of contact between the encapsulant and the active surface) can be more closely controlled. Any variation in the flowrate of encapsulant from the needle tends to cause bulges or valleys in the height of the bead and or the PCB side of the bead. The fluidic resistance generated by the gap between the barrier and the active surface means that the amount of encapsulant that flows into the gap and onto the active surface is almost constant. The reduced flow variations make the encapsulant front closely correspond to the shape of the barrier. Greater control of the encapsulant front allows the functional elements of the active surface of the die to be closer to the contact pads. 
     Preferably, the barrier is a profiling surface and the method further comprises the steps of: 
     moving the profiling surface over the active surface to flatten the bead of encapsulant. 
     Preferably, the method further comprises the steps of: 
     prior to depositing the bead of encapsulant, electrically connecting the contact pads on the die to respective conductors on the support structure with wire bonds, the wire bonds each extending in an arc from the contact pad to the conductor; 
     pushing on the wire bonds to collapse the arc and plastically deform the wire bond; and, 
     releasing the wire bonds such that plastic deformation maintain the wire bonds in a flatter profile shape. 
     In a further preferred form, the active surface that has functional elements, the contacts pad being formed at one edge of the active surface, the wire bond has a diameter less than 40 microns and the arc extends more than 100 microns above the active surface of the die. 
     Preferably, the wire bond is plastically deformed such that it extends less than 50 microns above the active surface of the die. In another preferred form, the wire bond is pushed by engagement with a blade having a rounded edge section for contacting the wire bond. 
     Preferably, the bead of encapsulant has a profiled surface that is flat, parallel to and spaced less than 100 microns from the active surface. 
     Optionally, the bead of encapsulant has a profiled surface that is flat and inclined relative to the active surface. 
     Preferably, the encapsulant being an epoxy material has a viscosity greater than 700 cp when uncured. 
     Preferably, the encapsulant is an epoxy material that is thixotropic when uncured. 
     Preferably, the active surface has functional elements spaced less than 260 microns from the contacts pads of the die. In a particularly preferred form, the die is an inkjet printhead IC and the functional elements are nozzles through which ink is ejected. Preferably, the printhead IC is mounted in a printer such that during use the nozzles are less than 100 microns from the paper path. 
     Preferably, the support structure has a chip mounting area and a conductor mounting area, the die is supported on the chip mounting area, and a plurality of electrical conductors at least partially supported on the conductor mounting area wherein, the chip mounting area is raised relative to the conductor mounting area. In a particularly preferred form, the chip mounting area is raised more than 100 microns relative to the conductor mounting area. In preferred embodiments, the support structure has a step between the chip mounting area and the conductor mounting area. In particularly preferred embodiments, the plurality of conductors are incorporated into a flexible printed circuit board (flex PCB) with a line of bond pads along an edge closest the die, the bond pads being more than 2 mm from the contacts pads on the die. 
     Preferably, the support structure is a liquid crystal polymer (LCP) molding. 
     According to a fifth aspect, the present invention provides a method of applying encapsulant to wire bonds between a die and conductors on a supporting substrate, the method comprising the steps of: 
     forming a bead of the encapsulant on a profiling surface; 
     positioning the profiling surface such that the bead contacts the die; and, 
     moving the profiling surface relative to the die to cover the wire bonds with the encapsulant. 
     Wiping the encapsulant over the wire bonds with a profiling surface provides control of the encapsulant front as well as the height of the encapsulant relative to the die. The movement of the profiling surface relative to the die can closely controlled to shape the encapsulant to a desired form. Using the example of a printhead die, the encapsulant can be shaped to present an inclined face rising from the nozzle surface to a high point over the wire bonds. This can be used by the printhead maintenance facilities to maintain contact pressure on the wiping mechanism. This is illustrated further below with reference to the drawings. However, it will be appreciated that the encapsulant can be shaped to have ridges, gutters, grooves and so on by using a particular shape of profiling surface and relative movement with the die. 
     Preferably, the method further comprises the steps of: 
     dipping the profiling surface into a reservoir of the encapsulant material to form a the bead of encapsulant material on the profiling surface. 
     Optionally, the profiling surface is a blade with a straight edge and the method further comprises the steps of: 
     orienting the blade such that the straight edge is lowest and dipping the straight edge into the encapsulant material to form the bead of encapsulant along the straight edge. 
     Preferably, the die has an active surface with functional elements and a plurality of contacts pad being formed along one edge for connection with the wire bonds such that the wire bonds extend in an arc from the contacts pads to each of the conductors respectively, the wire bonds having a diameter less than 40 microns and the arc extends more than 100 microns above the active surface of the die. 
     Preferably, the method further comprises the steps of: 
     prior to encapsulation, pushing on the wire bonds to collapse the arc and plastically deform the wire bonds; and, 
     releasing the wire bonds such that plastic deformation maintains the wire bonds in a flatter profile shape. 
     Preferably, the wire bond is plastically deformed such that it extends less than 50 microns above the active surface of the die. Preferably, the wire bond is pushed by engagement with a blade having a rounded edge section for contacting the wire bond. 
     Preferably, the encapsulant covering the wire bonds has a profiled surface that is flat, parallel to and spaced less than 100 microns from the active surface. 
     Preferably, the bead of encapsulant having a profiled surface that is flat and inclined relative to the active surface. 
     Preferably, the encapsulant being an epoxy material has a viscosity greater than 700 cp when uncured. 
     Preferably, the encapsulant is an epoxy material that is thixotropic when uncured. Preferably, the functional elements are spaced less than 260 microns from the contacts pads of the die. In a further preferred form, the die is an inkjet printhead IC and the functional elements are nozzles through which ink is ejected. Optionally, the printhead IC is mounted in a printer such that during use the nozzles are less than 100 microns from the paper path. 
     Preferably, the support structure has a chip mounting area and a conductor mounting area, the die is supported on the chip mounting area, and a plurality of electrical conductors at least partially supported on the conductor mounting area wherein, the chip mounting area is raised relative to the conductor mounting area. In a particularly preferred form, the chip mounting area is raised more than 100 microns relative to the conductor mounting area. In another preferred form, the support structure has a step between the chip mounting area and the conductor mounting area. In a preferred embodiment, the plurality of conductors are incorporated into a flexible printed circuit board (flex PCB) with a line of bond pads along an edge closest the die, the bond pads being more than 2 mm from the contacts pads on the die. In some embodiments, the support structure is a liquid crystal polymer (LCP) molding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic representation of a common prior art technique for applying a bead of encapsulant to wire bonds; 
         FIG. 2  is a schematic representation of a die mounted to a supporting structure with a chip mounting area raised relative to the flex PCB mounting area; 
         FIGS. 3A ,  3 B and  3 C are schematic representations of the encapsulant bead being profiled into a desired shape using a moveable blade; 
         FIGS. 4A to 4D  are schematic representations of wire bonds being profiled by plastic deformation; 
         FIGS. 5A and 5B  show the encapsulant bead height reductions for plastically deformed wire bonds; 
         FIGS. 6A to 6C  show the encapsulant bead being applied to the wire bonds using the profiling blade; and, 
         FIGS. 7A and 7B  show the profiling blade being used to control the encapsulant bead front on the surface of the die. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a common technique used for applying a bead encapsulant to wire bonds. A die  4  is mounted to a supporting structure  6  adjacent the edge of a flex PCB  8  (flexible printed circuit board). The die  4  has a line of contact pads  10  along one edge and the flex PCB  8  has corresponding bond pads  12 . Wire bonds  16  extend from the bond pads  10  to the bonds pads  12 . Power and data is transmitted to the die  4  via conductive traces  14  in the flex PCB  8 . This is a simplified representation of the dies mounted within many electronic devices. The printhead IC dies mounted to the LCP (liquid crystal polymer) molding to receive print data from an adjacent flex PCB, as described in U.S. Ser. No. 11/014,769 incorporated herein by cross reference, is one example of this type of die mounting arrangement. The ordinary worker will appreciate that the die may also be mounted directly to a hard PCB with traces formed thereon. 
     The wire bonds  16  are covered in a bead on encapsulant  2  to protect and reinforce the bonds. The encapsulant  2  is dispensed from a discharge needle  18  directly onto the wire bonds  16 . Often the encapsulant bead  2  is three separate beads—two beads of so-called ‘dam’ encapsulant  20 , and one bead of ‘fill’ encapsulant  22 . The dam encapsulant  20  has a higher viscosity than the fill encapsulant  22 , and serves to form a channel to hold the fill encapsulant bead. The height H of the bead  2  above the die  4  is usually about 500-600 microns. In most electronic devices, this does not pose a problem. However, if the die has an active surface that needs to operate in close proximity to another surface, this bead can be an obstruction. 
     Elevating the Die Relative to the Flex PCB 
       FIG. 2  shows a stepped support structure  6  that has raised the chip mounting area  26  relative to the PCB mounting area  24  (or at least the area mounting the PCB bonds pads  12 ). With the die  4  on a raised chip mounting area  26 , the arc of the wire bonds  16  are lower relative to active surface  28  of the die  4 . In fact, the end of the wire bond  16  attached to the contact pad  10  can be the apex of the arc (bearing in mind that the wire bond arc is intended to accommodate some relative movement of the die and PCB). When the wire bonds  16  are covered with encapsulant  2 , the bead has a reduced height H above the active surface  28  of the die  4 . If the bead of encapsulant  2  uses two beads of dam encapsulant  24  and a fill encapsulant  22 , the positions, volumes and viscosities of the beads need to take the step into account. Bead heights less than 100 microns are easily achievable, and with additional measures, such as wire arc collapsing and bead profiling (discussed below), bead height of less than 50 microns are possible. 
     With the die  4  raised above the flex PCB  8  by 410 microns, the height of the wire bonds  16  above the die is about 34 microns. With the die raised  610  microns above the flex PCB, the wire bond height is around 20 microns. Raising the die even further has shown little or no further reduction in wire bond height with a step of 710 microns having a wire bond height of around 20 microns. 
     Shaping the Encapsulant Bead with a Profiling Blade 
       FIGS. 3A to 3C  show the encapsulant  2  being profiled with a profiling blade  30 . The support structure  6  is again stepped to reduce the height of the wire bonds  16  above the die  4 . Before the epoxy encapsulant  2  has cured, the profiling blade  30  moves across the die  4  and wire bonds in a predetermined path. As shown in  FIG. 3B , the blade  30  displaces the top of the bead  30  to its flex PCB side to form a flat top surface  32  that is at a significantly reduced height H above the die  4 . 
     The encapsulant bead  2  may be a plurality of separate beads as shown in  FIGS. 1 and 2 , or a single bead of one material. However, for close dimensional control of the profiled encapsulant, the encapsulant materials used should be thixotropic—that is, once deposited from the discharge needle, or profiled by the blade  30 , the material should not flow under its own weight, but rather hold its form until it cures. This requires the epoxy to have an uncured viscosity greater than about 700 cp. A suitable encapsulant is DYMAX 9001-E-v3.1 Chip Encapsulant produced by Dymax Corporation with a viscosity of approximately 800 cp when uncured. The blade  30  may be ceramic (glass) or metal and preferably about 200 microns thick. 
     It will be appreciated that the relative movement of the blade  30  and the die  4  can be precisely controlled. This allows the height H to be determined by the tolerance of the wire bonding process. As long as H is greater than the nominal height of the wire bond arc above the die, plus the maximum tolerance, the encapsulant  2  will cover and protect the wire bonds  16 . With this technique, the height H can be easily reduced from 500-600 microns to less than 300 microns. If the heights of the wire bond arcs are also reduced, the height H of the encapsulant bead can be less than 100 microns. The Applicant uses this technique to profile encapsulant on printhead dies down to a height of 50 microns at its lowest point. As shown in  FIG. 3C , the lowest point is at the encapsulant front and the blade  30  forms an inclined face  32  in the top of the bead  2 . The inclined face is utilized by the printhead maintenance system when cleaning the paper dust and dried ink from the nozzle face. This illustrates the technique&#39;s ability to not just reduce the height of the encapsulant bead, but to form a surface that can perform functions other than just encapsulate the wire bonds. The edge profile of the blade and the path of the blade relative to the die can be configured to form a surface that has a multitude of shapes for a variety of purposes. 
     Plastic Deformation of the Wire Bond Arcs 
       FIGS. 4A to 4C  show another technique for lowering the profile of wire bonds.  FIG. 4A  shows the die  4  connected to the flex PCB  8  via the wire bonds  16 . While the stepped support structure  6  has lowered the height of the wire bond arcs compared to a flat supporting structure, the wire bonds still have a natural tendency to bow upwards rather than downwards towards the corner of the step. The wires  16  are typically about 32 microns in diameter and have a pull force of about 3 to 5 grams force. The pull force is the tensile load necessary to break the connection to the contact pad  10  or the bond pad  12 . Given the fragility of these structures (one of the reasons encapsulant is applied), conventional wisdom is to avoid any contact between the wire bond arcs and other solid surfaces. 
     As shown in  FIG. 4B , the arc of the wire bonds  16  can be collapsed by a wire pusher  34 . The wire pusher  34  displaces the wire bond  16  enough to elastically and plastically deform the arc. The Applicants have shown that contact with the wire pusher  34  can cause localized work hardening in the wire, but as long as the pushing force is not excessive, it does not break. The end of the wire pusher  34  is rounded to avoid stress concentration points. The wire pusher may be a stylus for engaging single wire bonds or a blade that pushes on multiple wire bonds simultaneously. 
     Referring now to  FIG. 4C , the wire pusher  34  is retracted and the wire springs back toward its original shape to relieve the elastic deformation. However, the plastic deformation remains and the wire bond height above the die  4  is much reduced. Testing has shown that an initial wire bond loop height of 200 microns can be reduced to about 45 microns using this technique. Tests have also shown that the pull strength of the plastically deformed wires remains at about 3 to 5 grams force. 
     The collapse of the wire bonds is uncontrolled and leaves the wire bonds somewhat randomly deformed. However, pushing the wire bonds closer to the die provides more uniformly shaped collapsed wire bonds. The Applicant&#39;s work has shown that engaging the wires about 200 to 300 microns for the die provides the best results. 
     As shown in  FIG. 4D , the die  4  and the flex PCB  8  are mounted to a flat support structure  6 . As discussed above, this means the original loop height of the wire bond arc is much higher—approximately 400 microns above the die  4 . Consequently, the wire has more plastic deformation when the loop is collapsed by the wire pusher. Even so, the Applicants results show that the residual loop height after pushing is about 20-50 microns. 
       FIGS. 5A and 5B  show the collapsed wire bonds  16  covered with an encapsulant bead  2 . Even without bead profiling prior to curing, the height H of the bead above the die is much less than the bead necessary to encapsulate the original undeformed wire loops. 
     Applying Encapsulant with Profiling Blade 
       FIGS. 6A ,  6 B and  6 C show the application of the encapsulant bead using the profiling blade  30  instead of a discharge needle (see  FIGS. 1 and 2 ). As previously discussed, the flowrate of encapsulant from the discharge needle can vary and this gives rise to large variations on the position of the encapsulant front on the active surface of the die  4 . Consequently, any functional elements in the active surface of the die need to be sufficiently spaced from the contacts pads  10  to allow for the meandering encapsulant front. 
     Applying the encapsulant with the profiling blade avoids the problems caused by the flowrate fluctuations from the discharge needle. As shown in  FIG. 6A , the bead of encapsulant  40  can be formed on the profiling blade  30  by simply dipping it into a reservoir of uncured encapsulant epoxy. Of course, the bead  40  may also be formed by any other convenient method, such as running the discharge needle along one end of the blade  30 . 
       FIG. 6B  show the blade  30  having been lowered to touch the bead  40  onto the die  4 . When the encapsulant material touches the die surface, it wets and wicks along the surface while remaining pinned to the edge of the blade. The blade  30  is held at a predetermined height above the die  4  and moved over the bead  2  to flatten and lower its profile. The encapsulant displaced from the top of the bead  2  by the blade  30 , spreads over the PCB side of the bead  2 . It is not relevant if the encapsulant spreads further over the PCB than necessary. As long as the wire bonds  16  and the bonds pads  12  are covered, any additional encapsulant on the PCB  8  surface is not detrimental. 
     In  FIG. 6C , the wire bond  16  height has been reduced by collapsing the arc in accordance with the techniques discussed above. As previously discussed, the bead  2  deposited by the discharge needle need not be as big to cover the wire bond  16  once it has been collapsed. Furthermore, the blade  30  can be brought closer to the die  4  without contacting wire bonds  16  when profiling the encapsulant  2 . Hence the bead profile in  FIG. 6C  is substantially lower than that of  FIG. 6B . 
     Encapsulant Front Control 
     When the encapsulant material is dispensed from the discharge needle, minor variations in the flowrate can cause the bead to bulge at points of higher flow. Consequently, the side of the bead that contacts the active surface of the die is not straight, but has significant perturbations. These perturbations have to be accommodated between the contact pads and any functional elements on the active surface. The spacing between the contacts pads and the functional elements consumes valuable ‘chip real estate’. The Applicant has previously developed printhead dies with a spacing of 260 microns between the contact pads and the first row of nozzles. Better control of the encapsulant front reduces the space between the contacts and operational elements, and so the overall dimensions of the die. Hence the design can be more compact and more chips fabricated from the original wafer disc. 
     As shown in  FIGS. 7A and 7B , the profiling blade  30  is used to control the front  36  of the bead of encapsulant  2 . The blade  30  is positioned over the die  4  to define a gap  42  between its lower edge and the active surface  28 . As the discharge needle  18  dispenses the encapsulant material  44 , it flows onto the active surface, one side of the blade and a fillet of the material extends through the gap  42 . Because of the flow restriction created by the gap, flow variations have a reduced effect on the dimensions of the fillet that flows through the gap. Therefore the encapsulant front  36  closely corresponds to the line of the lower edge of the blade  30 . 
     As shown in  FIG. 7B , the profiling blade  30  is already in position to profile the encapsulant bead  2  once it has been dispensed from the discharge needle. The blade  30  simply moves over the die  4  in a direction away from the nozzles  38 . This keeps the encapsulant front  36  in place and flattens the profile of the encapsulant bead  2  over the wire bonds  16 . 
     The invention has been described herein by way of example only. The ordinary will readily recognize many variations and modifications which do not depart from the spirit and scope of the broad inventive concept.