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Bonding of NTC Chip
2019/12/27 03:12:00


NTC chip produced by EXSENSE Electronic Technology Co., Ltd. has the characteristics of great reliability, high sensitivity and high precision (can up to ±0.1%), which is widely used in bonding, welding, temperature sensors, medical equipment, etc..With the development of electronic technology, electronic components will be developing in the direction of high performance, miniaturization and chip-based development. As a core component, NTC chip constitutes various NTC thermistors and temperature sensors in different packaging forms. It is widely used in various temperature monitoring, temperature control and temperature compensation in circuits, which plays a core role in converting temperature variables into required electronic signals.


At present, most NTC thermistors are made by preparing NTC chips, then welding leads and encapsulating them, and testing performance parameters after packaging is completed. However, the thermistors made through existing methods have the following disadvantages:


First, easy to be welded bad: with two leads to clamp NTC chip into the tin furnace , because of the tin furnace temperature, tin-immersing time and tin quality differences, which is easy to cause NTC chip continuous tin electrodeposit, thus forming a short circuit, resulting in poor performance;


Second, easy to be encapsulated bad: encapsulation is to coat the NTC chip with epoxy resin after welding leads in the sealing groove, and then cure it under certain curing conditions. If the chip is askew during welding, or the epoxy resin has different viscosity, it is easy to cause the uneven size of the product head after sealing.


In order to solve the above problems, EXSENSE Electronics introduce a bonding method of NTC chip, the use of automation equipment, so that the production process becomes more standardized. Easy operation, reduce the human factors caused by the probability of bad products. The specific operating process of this method is as follows:


First, preparation

(1) Inspection: check whether there is mechanical damage on the surface of NTC chip and whether the electrode pattern is complete; Measure whether the size of NTC chip and electrode meet the process requirements.

(2) Cleaning: using ultrasonic to clean LED bracket, and drying.

(3) Expansion: Because the NTC chip is still tightly arranged after slicing, the spacing is very small (about 0.1mm), which is not conducive to the operation of the subsequent operation. The membrane of the bonded NTC chip is expanded with a expander, stretching the spacing of the NTC chip to about 0.6mm. It can also be expanded by hands, but it can easily cause the chip to drop.


Second, die bond

(1) Dispensing: the automatic dispensing machine is used to add silver glue to the corresponding position of the LED bracket.

(2) Racking: the use of automatic racking machine NTC chip suction moving position, and then placed in the dispensing bracket position.

(3) Sintering: under certain sintering conditions, the NTC chip is fixed by solidifying the silver adhesive


Third, Bonding

The purpose of Bonding is to direct the electrode to the NTC chip and complete the connection of the internal and external leads of the product. The use of aluminum wire bonding machine or gold wire bonding machine, on the basis of thermal pressure to increase ultrasonic energy to achieve the connection process between the chip and lead frame.


Bonding process of NTC chip has gold wire ball bonding and aluminum wire bonding. Aluminum wire pressure welding is the first point on the chip electrode of the LED product, and then the aluminum wire is pulled above the corresponding bracket, pressing the second point after tearing off the aluminum wire. The process of golden wire ball bonding is to burn the ball before pressing the first point, the rest of the process is similar.


Fourth, encapsulating

There are three main type of thermistor encapsulating, dispensing, embedment and compression moulding:

(1) Dispensing: Protect the chip and bonding wire with epoxy resin. Dispensing encapsulation on the operating level is very high, the main difficulty is the amount of dispensing control, form factor is also difficult to maintain consistency, so it is not recommended to use dispensing packaging.

(2) Embedment: The process of dispensing is to inject liquid epoxy resin into the thermistor molding cavity, and then insert the bracket which the NTC chip is bonded, put it into the oven to make the epoxy resin cured, the thermistor is removed from the mold cavity and is molded.

(3) Compression moulding: the bracket of bonded NTC chip was put into the mold, the upper and lower molds were closed with hydraulic press and vacuumized, and the solid epoxy resin was put into the inlet of the rubber injection channel and heated by hydraulic push rod into the mold rubber channel. The epoxy resin was then transported along the epoxy resin enters each thermistor forming tank along the rubber channel and solidifies.


Fifth, curing

With certain curing conditions, epoxy resin is fully cured, and the bonding strength of epoxy resin and the bracket is improved, so that make them better protect the NTC chip.


Sixth, trimming

Due to the thermistors of bonding with LED bracket are connected together in production (not single), the connecting wires of LED bracket are cut off with trimming machine to test the performance of single thermistors.


Seventh, testing

Test the performance parameters of thermistors, check the external dimensions, and sort thermistors according to customer requirements.

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