Excessive solder

Soft-soldering of copper, iron, steel, and brass objects of large size is usually accomplished by the use of a burner or hand torch, with an acid flux—frequently a concentrated aqueous solution of zinc chloride and ammonium chloride (2 1 ratio)—brushed onto the hot metal concurrently with the addition of solder. Initially, heat should be applied around the area to be soldered but not directly on the region to be soldered. If the region to be soldered is heated too much without the application of flux, an oxide coating will form that can make proper surface adhesion impossible. The surfaces to be joined should be pretinned if possible, and excess solder is shaken off or wiped off with a cloth. The two surfaces to be joined are then placed in contact and heated with the torch until the solder begins to flow more solder is then added as required, and the pieces are allowed to cool undisturbed. The finished work should be washed thoroughly with water to remove the flux. 

The printed circuit boards and the various electronic components to be added to it are cleaned, trimmed and sorted. The components are then mounted on to the printed circuit board ( stuffing ). This can be done either by hand or by automated surface mount machines. The parts are then soldered on to the board, by immersion in wave solder baths, or by hand. Excess solder and wire is removed by hand in a touching-up process. The final product is marked and tested in a quality control check. 

If a lot of black material or other dirty coating is on the iron, scrape that off with the sharp blade of the wire stripper, replacing the dirt with shiny, cleanlooking melted solder. Add solder until a drop of it is sticking to the iron. Excessive solder might drip off the end, so make sure it only lands on the cardboard or paper. Melted plastic ("flux") might also drop, as well as evaporating upwards in the form of white smoke, but this is quite normal. 

Becanse of the extra operations and exposure of components on the secondary side to molten solder, this type of assembly is prone to many assembly defects. It is important to note that soldering fine-pitch parts on the secondary side using wave soldering results in excessive solder bridging and should be avoided. In addition, active components, such as ICs, may be damaged by exposure to excessive heating. 

Thickness. When PCBs had all through hole components, solder mask thickness was not of much concern. However, with the advent of surface-mount technology in the 1980s, excessive solder mask thickness caused assembly problems, including ... 

Dress the drcuit board solder pads by removing any excess solder while the latter is molten. 

The dressing of the through-hole and Cu pad is the next step. An excess of solder remaining in the hole will hinder lead insertion for the new component. It is difficult to extract physically all solder residue form inside a hole, even at modest aspect ratios (board thickness-to-hole diameter). This difficulty is further compounded with thicker,multilayer circuit boards because the soldering iron tip cannot compensate for the large thermal mass of the laminate or the heat-sink effects caused by the internal Cu layers. Finally, it is often necessary to contact the Cu pads of the circuit board briefly, with the braid between the pad and the tip, to remove any excessive solder residue. 

Once the defective component has been removed from the circnit board, the second step is to remove excess solder from the Cu pads. This step is also referred to as dressing the pads. Remaining solder bumps and spikes interfere with the placement of the new component. More importantly, excess residual solder, the quantity of which is not tightly controlled, causes variabihty to the replacement component s solder joints, which can lead to possible opens, shorts, or a loss of long-term reUabiUty. Eecanse the cleaning or dressing step requires a solder reflow heat cycle (the secx>nd of three), the time-temperature profile of that cycle must be... 

A new category of low solids fluxes was introduced in the early 1990s to meet the needs of localities where volatile organic compounds (VOCs) are regulated. These fluxes are marketed as VOC-free or low-VOC fluxes. The solvent in this case is 100 percent water or at least greater than 50 percent water. Use of these fluxes requires special care in the preheat step where the water (solvent) must evaporate before the assembly reaches the solder wave. Failure to do this will result in excessive solder ball formation. 

If excess solder beads are stiU apparent, the board should be recleaned. Try rotating the board 90° or 180° for the repeat cleaning cycle. 

PWB vendor to ensure that drilled and plated holes are sized appropriately for the press-fit process and that excess solder from the HASL process does not adversely alter the finished hole size or shape. 

Excess solder conditions that produce a solder fillet that is slightly convex or bulbous and in which the lead is no longer visible are considered defects for unsupported hole lead termination. 

Distribntion feedback Electrical noise Electrical snrges Electromagnetic interference Excessive solder Gronnding... 

Removal of the assembled lead-free, tin-coated PDIP was successful with a lead-free SnAgCu pot temperature of 274°C using about 15 to 20 seconds dwell time. Excessive solder was removed and the site was redressed. Reattaching a new component was found to be more challenging. 

Minimize the problem of copper pad/trace dissolution caused by excessive solder-contact times... 

Excessive solder voids can create reliability issues, especially in applications where the lead-free assembly is exposed to thermal... 

Systems developed for tin component lead finishes exhibit some problems. Flagging and icicles (excess solder condition) at the end of leads are particularly difficult to control and very troublesome for automatic and even hand insertion. The use of flux sprayed into the exit of the wave alleviates the problem, but also causes major contamination and maintenance problems. However, the use of nitrogen, instead of flux, results in a more uniform solder coating as icicles draw up on leads under inerted conditions. A number of these tinning systems are commercially available. 

Desolderlng tapes are used for absorbing excess solder on circuit boards. A minimal quantity of mild and neutral flux is included. The desoldering tape is highly-absorbant. 

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