Chip bonding

The term chip-bonding or die bonding (sometimes called bare chip bonding ) referred to in the electronics -production (semiconductor technology) the step of mounting the separated fragments ( bare chip , engl .: bare die ) of the wafer on a base plate.

The procedure

Bonding to a modern power transistor (the die was bonded to a copper carrier by means of chip bonding)

Chip and wire bonds of an older bipolar power transistor: the square chip is soldered with gold solder to a round carrier plate, which in turn is soldered to the metal housing. This connection dissipates the heat and forms the collector connection. The two wire bonds made from aluminum wire are the emitter (below) and the base connection (above), both of which lead on legs in glass feed-throughs (left).

The base plate can be the housing / heat sink of the finished component or, in the case of chip-on-board technology, a substrate that also carries other components (a printed circuit board , a ceramic substrate of a thick-film circuit ).

The bare chips are attached to the carrier using the following methods:

• Gluing : epoxy or silicone resin, some with non-metallic or metallic fillers (powder)
• soldering
  • Soldering with glass solder (angled glass)
  • Soldering with soft solder : is mainly used for power components in order to compensate for deviating thermal expansion coefficients to the heat sink (e.g. made of copper) due to the ductility. The process requires metallization of the back of the chip and must be carried out without flux under a reducing or protective gas atmosphere in order to avoid contamination. Reflow soldering and vapor phase soldering can be used as soldering processes . The soldering itself is usually carried out in a protective atmosphere. In the case of vapor phase soldering, the soldering process can sometimes be carried out under reduced pressure in closed systems. The soldering temperature is typically less than 300 ° C.
• Alloying, also known as eutectic soldering: between the silicon chip and a gold layer, a silicon-gold eutectic that melts below 400 ° C is formed by diffusion . Welding is often achieved with the help of ultrasound (US). However, this connection is brittle: especially with large chips, the carrier must be adapted to the silicon with regard to the thermal expansion coefficient.

In the case of many components, the back of the chip also has an electrical function (body contact, back contact) and is used to dissipate heat to a heat sink (cooling flange, cooling surface on copper or metallized ceramic), in which case it is only possible to bond with metal.

Die bonding is usually the last step before electrical contact is made by wire bonding . With the flip-chip construction, all contacts are made directly with the help of solder. For this purpose, a previously placed solder deposit is melted on each contact (see also Ball Grid Array ).

Individual evidence

1. ↑ Thomas Raschke: Montage / Bonding. (PDF, 735 kB) (No longer available online.) In: Internships for the courses Microelectronics and Microtechnologies. Formerly in the original ; Retrieved June 6, 2009 .  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.