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Introduction of Wire Bonding

Wire Bonding is one process in PCB assembly and the electronic manufacturing services industry. It uses gold wire or thread and utilizes thermal ultrasound or ultrasound to finish the connection of chips with the circuit or lead frame. In the bare chip microelectronic assembly(Micro assembly for short), wire bonding is universally used to achieve electronic interconnection, like chip-chip, chip-base board, and base board-base board.

Wire bonding is very important. One microelectronic component will have many interconnection leads. One invalid lead may cause the whole microelectronic components invalid. So to ensure the quality of the PCB wire bonding, during the process of PCB wire bonding, except strengthening the control of the process of wire bonding, we still need to check the function of the income material before acceptance.

Therefore, to lead the healthy development of the PCB wire bonding industry and to avoid fake and shoddy material (like the second hand or multi-handed cleaver will shorten the life of bonding), we need comprehensive standards development the test methods and acceptance criteria for the function of material (like wire diameter, elongation, breaking force, etc. ) and the function of a cleaver( appearance, size, bonding life) as well as the quality of wire after bonding( appearance, Non-destructive tension).
Wire bonding is the technology that connects the semiconductor chip bonding area with the i/o lead of the electronic packaging shell or the technical wiring bonding area on the substrate connected by metal filaments. A lot of automatic machines for batch production had been developed. The bonding parameter can be precisely controlled, and the time of formation of the interconnection conductor cycling process between two solder joints just needs 100ms-125ms. The gap had reached 50 μM. PCB wire bonding technology is the earliest interconnection method for semiconductors.

What is Wire Bonding Used for?

Wire bonding is used for completing the connection of the chip to the circuit or lead frame.

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    Our Wire Bonding Capabilities

    Thermal ultrasonic/gold wire ball welding

    This technology are use heating temperature and ultrasonic energy to form a welding bond between two metal interfaces that are pressed together and compressed tightly. Over 90% of semiconductor package technology use this method.

    Ultrasonic Wedge welding

    This technology uses ultrasonic energy to act on two metals pressed tightly together to form the bonding.

    Hot press welding:

    This technology are use heating and pressing force formation wire bonding. This technology was used in Bell Laboratories by 1957 and is the first bonding technology, but barely use now.

    Two types of Wire Bonding Techniques

    Wedge welding:
    First pressure welding point(cleaver move down, wire touch the pad, then exert heating ultrasonic or ultrasonic to finish the first pressure welding point) —- Cleaver up movement —- Complete linearity.
    Tips: This process mainly uses aluminum wire, but also can use gold wire, usually processing at room temperature. Wedge weld press down two wedge welds point to achieve the connection, there not have ball formation in this process. The aluminum wire welding process was classified as ultrasonic wire welding, just using ultrasonic energy, pressure and time, etc. to form the welding points. Because of different applying situations and different usage, we choose different types of processes.
    Spherical welding:
    First pressure welding point(cleaver move down, wire touch the pad, then exert heating ultrasonic or ultrasonic to finish the first pressure welding point–Spherical)—Second pressure welding point(cleaver move down, wire touch the pad, then exert heating ultrasonic or ultrasonic to finish the second pressure welding point–Wedge)— Cleaver up movement—-Reserved tail—-pull apart gold wire.
    Tips: In this process, a molten golden ball stuck to a section of wire, becomes the first welding point after pressing down. Then draw out the Crooked wire from the first welding point, then connect the line (the second wedge weld point) in a crescent shape, and then another new ball is formed for the first ball welding point of the next one. The gold wire spherical welding process was classified as a thermoacoustic process. In another word, the welding point is formed under the thermal (normally 150℃) ultrasonic, pressure and time, etc. comprehensive action.

    Gold Wire Bonding VS Aluminum Wire Bonding

    Gold wire bonding is used in mass production occasions, because this process is faster, while wire bonding of aluminum is used in encapsulation or can’t heating occasions of PCB.
    There are different requirements of pad gad distance for gold wire bonding and aluminum wire bonding. The smallest gap for gold wire bonding is 60um, but the gap for aluminum wire bonding can be less than 60um which is possible for high-density wire bonding requirements.

    The Advantages of Wire Bonding

    Wire bonding technology started in 1971 in power electronics and microelectronics. Also widely used in new energy cars industries by far, such as power battery connection devices. Some electric vehicles use PCB wire bonding technology in the connection between battery packs. Please check the picture below.

    Since 1971, wore bonding is extensively used in the microelectronics and power electronics field. A lot of electric vehicle manufacturers begin to use wire bonding technology in battery connection devices. May electronic car manufacturers are using wire bonding technology in battery connection parts, such as TESLA, BYD, WEE, Toyota, etc. In the year 2006, TESLA was a pioneer. They started to use wire bonding technology this technical mode to connect cells to a large battery pack.

    The engineers in TESLA think that the traditional welding technology is not robust enough, and the efficiency is low. Also, it is very difficult to test if the device is functionally good or not, so they use aluminum wire bonding. The advantage of aluminum wire bonding is: a certain amount of allowable range current passes through, but will be fused if there is short or over-range current.

    The engineers of TESLA believe other welding technology will cause electrical protection problems without fuse protection. A single cell may have an internal short circuit after failure or damage, which will cause other cells that are connected in parallel with it to fail to use.
    Traditional brazing soldering technology and fusion welding technology have some not-good characteristics after being used for many years. For example, there are problems with thermal stresses and not easy cleaning during the process. There is not enough flexibility and it is difficult to control the quality because it is not known what will happen during cleaning. Traditional welding techniques can have these problems but wire bonding is much better and better, wire bonding can very well control each solder part in the product, and there will not have adverse effects when you do the production process.
    • If you want to work under room temperature, you can use aluminum wire bonding or aluminum strip soldering. It can save the source of external temperature, the temperature in the soldering zone will keep the room temperature during ultrasonic friction welding. But if you like heating to melt the metal to finish soldering, then you can choose other traditional welding ways.
    • Wire bonding is good for environmental production. We don’t need any clean up after soldering at all, so no pollution to water or air. At the same time, we can save a lot of time on cleaning. But in traditional soldering technology, we have to clean up extra solder balls and metal lefts after production.
    • Flexibility and strong compatibility are very important for welding. Wire bonding happens to have these advantages in the PCB assembly process. There are other advantages. For example, the height is very low after wiring bonding compared to read-made IC chips with the package.
    • There are different wires with different characteristics that can be chosen according to your usage, the most important one is the thermal expansion parameters. You may choose the right one to avoid a mismatch in the PCB wire bonding process, and also cost-effective. After all, the metal wire can have good directional flexibility.
    • Everyone likes easy work, and also likes to reduce money by the investment of equipment. That’s why you need to choose PCB wire bonding because the bonding wire can be used as a fuse directly, saving the extra resistance welding to solder Nickel sheet.

    Common Defects in Wire Bonding and Analysis

    Pin bonding cocking

    Manifested as: Test failure (short)

    Causes: 1. Pin surface oxidation, 2. Bonding parameters are not optimized.

    Short circuit between adjacent Bonding ball

    Manifested as: Test failure (short)
    Causes: 1, Bonding parameters are not optimized. 2, Bonding ball size and thickness are not optimized.

    Short circuit between the gold wire and the grounding pin

    Manifested as: Test failure (short)
    Causes:1. Wire radian data not optimized; 2. Wire radian height set incorrect.

    Short between upper strata wire radian and lower stratum wire radian

    Manifested as:Test failure (short)
    Causes: Wire radian data set incorrect.

    Most Important Chip Pad Design Rules in Wire Bonding

    1, In PCB, the length of the gold finger needs to be the same around the DIE position. The distance between the gold finger and DIE is 0.5-3.5mm. The difference between the distance between the gold finger and the surrounding areas should not exceed 20%.
    Reasons: When the height of the IC exceeds a certain height, will affect the data setting(wire radian setting) of the bonding machine. If the data set is equal on the 4 sides, the operation is smooth. However, if the data settings of the 4 sides are not equal, it will often lead to broken lines.
    2, The picture below shows the height of the SMT components. The view of the picture is the top of the PCB gold finger.
    In the annular area of the A.B.C.D.E representative, the Respective is not over the height of 0.6mm. 2mm. 6mm. 2.2mm.4mm components( This height is the height of the component after the PCB assembly). Other areas are normal height components(do not have height limits).
    Reasons: If the height of the component exceeds the area shown in the picture, the effect of the soldering on the top will be affected. If this part of the component is left to the end to be soldered by hand, it is the efficiency and quality of manufacturing will be not ensured.
    3, The shape of the Contraposition point for DIE needs to change from ‘十’ to the shape above.
    Reason: If the shape does not change, the bonding machine is difficult to have a better recognition effect.

    4, From observing the mask points of the bonded chip on the right, we can see that the edges of the PCB and the two right-angled sides of the triangle are perpendicular to each other and they are in balance with each other.

    Reason: If all the Mask points of bonding chips, the two right angle sides of the triangle are not perpendicular to & not balanced with the edges of the PCB, it will affect the accuracy of identification for the bonding machine.


    5, The silkscreen width in DIE is 20 mil. Here is a tip: Do not arrange the position of the vias inside the white oil frame.

    Reason: The flow direction range of the black glue is limited to the white oil frame of the DIE. If there are vias inside the white oil frame, the black glue will flow to the other side of the PCB through the vias, and then the performance of other components will be affected.

    Introduction of Bonding Adhesive

    Bonding adhesive is the adhesive for the bare IC chip package, Common name: black adhesive or COB (Chip-on-Board) bonding adhesive. The classification of the bonding adhesive in the market is Cold adhesive B-313, Hot adhesive B-919, and Cold sealing hot adhesive.

    Bonding adhesive main material:

    Base material (main high molecular material), filler, curing agent, other assistant material, etc.

    The Function of bonding adhesive:

    There will be good protection, splicing, and leakage prevention for IC and crystal plates.

    Classification of bonding adhesive:

    There are hot adhesives, cold adhesives, gloss adhesives, matte adhesives, high adhesives, and low adhesives.

    Production Processes of Wire Bonding

    Technology processes:
    Clean PCB pad→Drop bonding adhesive to the welding point →Paste the chip in PCB→wire bonding→sealing the adhesive→test.

    Introduction of PCB Wire Bonding Machine

    A bonding machine is a kind of production equipment widely used in the electronic manufacturing service industry. It adopts the pulse heating method and coordinates with the titanium alloy hot press head to realize the function of rapid heating and cooling and accurate temperature control, which effectively ensures the quality of products. It is mainly used for digital tubes, lattices, integrated circuit soft packaging, thick mold integrated circuit, transistor, and other semiconductor devices’ internal lead welding.

    The working principle of bonding machine:

    The bonding machine is a full-featured COB soldering equipment. It is a device that can precisely position IC chips on LCD glass and complete the soldering line. The whole machine consists of PLC+HMI as the control core. The automatic image alignment system PV310 completes the alignment data calculation of the target object. After the product is finished with alignment and pre-press work, it will be transported through the platform to the actual pressure for soldering.

    The bonding machine has the special function of quantitative memory for aluminum wire data, such as wire gap, check height, and archwire height. So it is more suitable for welding aluminum wire with many different data, such as integrated circuits and thick-mode integrated circuits. Soldering of inner leads of semiconductor devices can be performed for digital tubes, lattice boards or backlights if the memory function is set to “Reserved”.
    The bonding tool frame of the bonding machine uses a vertical guide rail up and down movement method (Z-direction motion), second welding moving past the bonding tool frame by horizontal guide rail movement (Y–direction motion) to achieve. Both movements are driven by an imported stepping motor, so the first welding and second welding can truly achieve digital control for aiming height, arch wire height, and wire jumper distance, thus guaranteeing the stable quality of welding, welding point accurate control, high repeat rate of welding wire, good identical archwire height.
    In addition, second welding can set to automatic welding, the operator just need to press the welding button in the operation box, then it can finish the whole welding process according to the data that set by the operator, that make the welding speed quicker, also can substantially increase the yield of each class.
    The performance characteristics of bonding machine

    CCD vision system, provides precise alignment.


    Multi-segment temperature raise control, temperature control precisely.


    Temperature curve display in real-time, simple operation. The operator does not need to use the instrument to test the temperature. The system can automatic detection and adjust.


    Have a single working platform, rotating working platform, left and right movement working platform, etc. Working mode can achieve multi-group products continuity working, improve work efficiency.


    Adopt high-quality accessories and finish machining parts that import from other countries, strong wear resistance, easy installation, and high accuracy welding.


    In the operation interface, the system will show the running state of every part. It also can test every function automatically and will display alarms right away when having any faults.

    The whole machine possesses an automatic reset function and can make sure to automatically reset back to the working origin in any working condition.
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    Frequently Asked Questions

    Gold, Aluminum, and copper wire bonding are mainly used in wire bonding.

    As mentioned above, the process of wire bonding is as follows.

    Clean PCB pad→Drop bonding adhesive to the welding point →Paste the chip in PCB→wire bonding→sealing the adhesive→test.

    1) Wirebonding is good for environmental production.
    2) Wirebonding has flexibility and strong compatibility.
    3) Wirebonding can be used as a fuse directly, saving the extra resistance welding to solder Nickel sheet.

    Wire bonding is mainly used in semiconductor Industries, but it is also widely used in all industries.

    1. The operator should wear suitable labor protection products before work, such as dust masks, welding gloves, and welding overalls; goggles or masks should be worn during operation; rubber shoes should be worn when working in wet places or on rainy days.
    2. Do not store flammable and explosive substances in the room and site for welding operations. If welding is required, flammable and explosive materials must be removed first, and strict isolation measures should be taken if there are difficulties to prevent fire and explosion accidents caused by welding sparks and red-hot particles splashing.

    Yes, they are the same, both use wire bonding technique to bonding wire and pads together.