Flying Probe test

Flying Probe test is to test some of the major problems of electrical latest solutions. To replace it with a probe needle bed, a plurality of motor-driven can quickly move the probe with the Rigid-flex pcb devices of the pin contact and electrical measurements. This instrument was originally designed as a bare board, also requires sophisticated software and program support; has now been able to effectively simulate the online test. Flying Probe Test appearance has changed the test method and the low yield rapid conversion (quick-turn) assembled products. Used to take weeks to develop a test a few hours now, and greatly shorten product design cycles and time to market.

Rapid test development; low cost test methods; flexibility fast conversion; well as in the prototype stage to provide rapid feedback to the designer. Therefore, comparing the traditional ICT, Flying Probe test by reducing the time required to make up for the total test time. Flying Probe test system using the benefits outweigh the disadvantages. For example, during assembly, such a CAD system file received after the start of production hours. Therefore, to test the prototype circuit boards for several hours after assembly, not like ICT, high-cost test development process and fixture may be delayed a few days or even a few months. In addition, due to the simple and quick setup, programming and testing, in fact, the general assembly of technical personnel, and not an engineer, you can operate the test. Flying Probe test also exist the flexibility to do a quick test errors quickly convert and process feedback. Also, because the test does not require flying fixture development costs, so it is a typical testing process can be placed in front of the low-cost systems. And because Flying Probe Tester change and rapid test method to convert low-yield assembly, testing usually takes a few weeks to develop a few hours you can get now.

Automatic optical alignment system and the traditional combination of flying machines, the entire automatic optical alignment can make flying more convenient testing and flying in the image processing software dedicated to digital cameras with the help of more accurate. In the traditional Flying Probe test machine, the installation of Flying dedicated to digital cameras and the corresponding image processing software; flying probe testing throughout the automatic identification and detection of the corresponding position to make flying safe and fast test. Having regard to the requirements for fast and precise flying machine, solid industrial hardware and graphics hardware choice, you should first take into account the lightweight, industrial, optical distortion-free, high-speed image processing algorithms; such testing in the actual process of flying because the industry does not appear to affect the hardware itself, the weight of the test accurate, does not appear lost step, and does not affect the image processing algorithm speed flying probe test.

Electroless Copper Plating

Metallization is required on the wall of the drill holes to make them conductive. It can be done by chemical deposition or direct metallization. For double layer boards, chemical deposition is common. It is an electroless process because the deposition of copper is done in the absence of electrical current. The objective of the electroless copper plating process is to deposit a very thin layer of copper over the entire surface of the copper cladding and on bare hole walls. This layer should be thick enough to allow the electrical current during the subsequent electrolytic plating. Normally, a thickness of 0.001 Mil to 0.0025 Mil is acceptable for further electroplating at low start current. The thickness of the PTH will be increased to the required level after the electrolytic copper plating.

Several proprietary solutions are available for making electroless copper. Basically, a precious metal palladium is being used as an activator to provide a site for the adhesion of electroless copper. Electroless copper bath contains an alkaline chelated copper reducing solution that deposits thin layer of copper on activated surface.
The thickness of electroless copper needed can be observed from the following table which gives the thickness of copper foil on Aluminum pcb. For reliable operation, PTH wall thickness should be around 0.7 Mil to 1 Mil.

Electroless copper plating process is consists of 4 baths; acid predip bath, activator bath, postactivator bath and electroless copper bath. Most of the process can be done at room temperature. We'll use PTH process chemicals from Enthone-OMI as an example. Circuitprep 3023 is used to prepare the acid predip bath. It is a low acid solution to replace a bath of high concentration hydrochloride acid. An immersion for 1 - 2 minutes in Circuitprep 3023 is sufficient to attain balance in the activator bath. The preparation of this bath is simple, 100% concentration is needed. It should be noted that no water should be allowed from this bath onward until the PTH process is completed.

The next bath is the Circuitprep 3316 palladium catalystic process. Major ingredients are palladium chloride and hydrochloric acid. This is a catalyst for electroless deposition on insulators. This process should provide uniform void-free metal coverage in holes and good electroless copper to copper clad adhesion.

The next bath is the Circuitprep 4044 postactivator process. Working in conjunction with CP3316, CP4044 accelerates the initial deposition of copper onto an activated surface. Mechanical agitation is required to ensure the removal of air bubbles in the holes and a complete wetting of the PCB. The active ingredient is fluoboric acid. It remove the protective stannous from the CP3316 so that electroless copper can adhere to the activated surface easily.

Enplate CU-406 concentrates are used for electroless copper disposition. Heater is normally required in electroless copper bath. The solution itself is highly unstable and we made use of its thermal property to restrict the displacement of copper from the solution. Thus, depending on the formula, temperature can be used to control the process so that it won't precipitate all the copper when the solution is idling. In fact, a cooling coil can be installed in the bath to cool it down to around 12 ° C to save it for a longer period in time.

FPC soldering Technology

Should adopt mandatory infrared reflow furnace hot air convection, so the temperature on the FPC can evenly changes, which reduce the generation of bad welding.If using a single side tape, because it only fix the four edges of FPC, because in the condition of hot deformation, the middle part of bonding pad tends to tilt, molten tin (under the high temperature of liquid tin) will flow to generate empty welding, soldering, tin beads, make the process defective rate is higher.

1) temperature curve test methods:
    Due to the Heat absorptivity is different to the load Flexible pcb , difference type of components on FPC, the difference of their temperature rising speed after heated during reflow soldering, have different heat absorption, so carefully set reflow furnace temperature curve will bring great influence to welding quality. Relatively reliable method is, according to the plate spacing during actual production, put two sheet of the load board which with FPC in front and behind of the test board, at the same time, the FPC on the load board sticked with components, with high temperature solder wire to weld the test temperature probe onto the test points, at the same time use high temperature resistant tape to fix the probe wire onto the load board. Note that high temperature resistant tape can not cover the test point. Test point should be adopted the solder points which near the load board edges and the QFP pin, in this way the test result can better reflect the real situation.

2）Setting of the temperature curve：
During furnace temperature debugging, because the average warm to FPC is NG, thus it's best to adopt heating/insulation/reflow temperature curve method, so that each area’s parameter is easy to be control led, others, influence of heat shocks to FPC and other components will be smaller. Based on experience, the best temperature will be dispatched to the lower limit of solder paste technical requirements value, wind speed of furnace is generally adopt the minimum wind speed, chain of reflow furnace’s stability should be, can't have.

Conclusion: When doing SMD mounting on FPC, the top importance is to realize accurate positioning and fixation, the key for fixation if to make an appropriate load board, and the second importance is the prebaking, tin printing, mounting and reflow soldering to FPC. Difficulty to FPC soldering is obvious higher than to rigid PCB. so it is necessary to accurately set the process parameters,at the same time, strict production process control is also important, must ensure that operators strictly implement each regulation on SOP, engineer who track the line and IPQC should strengthen the inspection,  Discover the unusual situation of production line in time，with line engineers and IPQC inspection should be strengthened, timely discover the unusual situation of production line, analyze the reason and take the necessary measures so that can control the FPC SMT production line NG rate within scores of PPM.

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