Plate curing technology

Batteries intended to be used within 2 or 3 months after manufacture are produced with lead—ealeium—tin alloys, filled with electrolyte and ready for use. In this case, the technological scheme in Fig. 2.52 is modified. The tank formation and plate drying steps are eliminated and plate curing is followed by battery assembly, the formation process being completed in the battery itself. 

A sample scheme of the successive technological procedures involved in the process of 3BS paste preparation is presented in Fig. 6.32. An example of a formulation for 3BS paste preparation could be LO (78% PbO) — 500 kg, H2O — 65 L, H2SO4 (1.4 g cm ) — 39 L, fibres — 0.35 kg. For the conversion of the 3BS paste into 4BS during the plate curing procedure, some 6—7 kg of tetrabasic lead sulfate nucleants should also be added to the initial paste mix. 

The processed products range from cured laminates or Inks to lithographic plates and copy papers to memory and logic computer circuits. The curing systems are a new technology which offers low costs. 

Positive plates need much more time to form than negatives. The reason for this is the dielectric behaviour of the cured positive paste. Oxidation of the bivalent lead compounds in the paste and formation of the Pb02 positive active mass passes through a number of chemical reactions, some of which proceed at a low rate, which retards the technological process of formation of the positive plate. In an attempt to accelerate the formation process, additives to the positive paste have been looked for, which are characterised by electro-conductive properties and stability in sulfuric acid. These additives create an electro-conductive network in the paste and the process of oxidation proceeds simultaneously within a large paste volume, thus accelerating plate formation. 

Figure 8.23 shows the interface paste/CL2 layer of a plate prepared with 3BS paste cured at 90 °C for 3 h and then treated with steam for another 2 h. Carbon dioxide is introduced into the curing chamber with the water steam [16]. The shape of the crystals formed under these conditions is typical of plumbonacrite and cerussite crystals. Obviously, the technology of 3BS conversion into 4BS through purging with water steam, i.e. introduction of CO2 from the air, leads to formation of hydrocarbonates at some sites of the paste/CL2 interface. 

The cured pastes of both positive and negative plates comprise identical mixtures of bivalent lead compounds (3BS, 4BS, PbO, Pb), which cannot create electromotive forces when the pasted plates are assembled into cells. The purpose of the technological process of formation is to convert the cured pastes into electrochemically active porous materials Pb02 in the positive plates and Pb in the negative plates, which are connected mechanically and electrically to the grids. The process of formation can be conducted via two basic technological schemes. 

The technology of plate preparation for this investigation is as follows paste prepared with H2SO4/LO = 6% by weight 4BS paste paste density 4.32 g cm curing at 90 °C or 50 °C and soaking in H2SO4 solution of 1.10 or 1.25 rel. dens. [4,20]. 

Zinc oxide is essential in rubber technology because it is the most commonly used activator for sulfur cure systems. Just about every rubber compound that uses sulfur as the vulcanizing agent will most likely contain a small amount of zinc oxide to activate the cure. Also zinc is alloyed with copper to form brass. Special brass-plated steel tire cord is a primary reinforcing material for producing steel-belted radial tires. The brass coating of the steel tire cord enables very good rubber-to-metal adhesion. Therefore, zinc metal and zinc oxide are very important to the rubber industry. 

A ribbed structure substrate was made by United Technologies Corporation (UTC). Pitch based carbon fibre about 0.12-0.25 mm long was blended with phenolic resin powder and laid on a steel belt for curing in a belt press. This was subsequently graphitized. This thick ribbed substrate (around 2-3 mm) was successfully used in UTCs 40 kw PC-18 power plants. The main purpose for such high thickness was to hold sufficient phosphoric acid and to have the flow fields (the ribbed structure) embedded on the substrate itself. Thus, costly high density graphite plates that were otherwise required for flow field and separator plate can be reduced in thickness for cost efficacy. 

A flip-chip technology developed by Toshiba Corporation utilized an ACF to attach bare umbumped chips (with A1 pads) onto a polychlorinated biphenyl (PCB) with bumps formed from a silver paste screen printed on the PCB [32]. After curing, Ag bumps were formed (70 pm diameter, 20 pm height), which were subsequently overplated with Ni/Au. It was determined that an ACF with a low CTE (28 ppm/°C), low water absorption rate (1.3%), and utiUzing a Au-plated plastic ball worked best. It was also found that Ni/Au-plated Ag paste-formed bumps exhibited a lower initial connection resistance and a lower connection resistance increase as compared to Ag paste-formed bumps that were not overplated with Ni/Au. The initial connection resistance for Ni/Au-plated Ag paste bumps and nonplated bumps was 22 and 48 pll, respectively, with a respective increase of 294 and 717 pO after 1000 hr of accelerated thermal cycling (ATC) testing. 

---