As WanTcom HMIC products use surface mount technology (SMT) on chip welding, there are no outwardly extending pins, so domestic manufacturers are less familiar with the welding processes of WanTcom products than traditional DIP/SOIC related packaging methods. The following summarizes the issues that need to pay attention during the whole design to production process of WanTcom products:
Product Design Issues When designing WanTcom MMIC, engineers are reminded to perform matching according to the external matching circuit provided by WanTcom, especially for the power and grounding parts of the chip. If engineers can get and provide matching circuit diagrams around the chip to WanTcom at an early design stage, WanTcom can provide relevant design advice to avoid complex modification work caused by design flaws, especially in military products, which are difficult to change after design finalization.
Electrostatic Protection Issues Most WanTcom products use GaAs materials, which have higher requirements for electrostatic protection. Although WanTcom has considered electrostatic protection circuits during chip design, it still need to remind clients of electrostatic protection issues during the inspection, surface mounting and testing of WanTcom products. Generally, it is best to use ESD gloves when touching the chips and ESD bracelets during testing.
Positioning Issues of the Chip on PCB
Establishment of Right-Angle Calibration Lines around the PCB Chip
The center box indicates the area of the chip on PCB. The distance between the 4 right-angle lines around the chip and the 4 angles of the chip is the same. When designing PCB, establish right-angle calibration lines. When carrying out manual design or manual small-batch production, calibration lines must be added to facilitate visual inspections to avoid chip offsets and chip dislocation short-circuits.
Shown in photo: Chip Position on PCB
Calibration of the Surface Mounting Machine and PLC Program Positioning during Mass Production
PLC program of the placement machine usually controls the chip position during mass production. Since WanTcom products are relatively small, the solder foots are also very small. Therefore, the calibration and program control of the surface mounting machine itself is very important as it directly affects the accuracy of the surface mounting.
Shown in Photo: Area Map of PCB Chip
Several Issues during Welding
Stencil production (For solder scraping)
Dispensing and Fixing (WanTcom chips cannot be dispensed as the bottom is the earthing area)
PCB reflow soldering
Extraction of the surface mounting machine has been considered in the whole package of WanTcom products. The above picture shows the standard package for WanTcom. When the surface mounting machine has the correct settings, there is no need to manually extract the chips as the machine can automatically weld.
Issues with Welding Area
Area A shown in the photo is the grounding area at the bottom of the chip. The opening area of the stencil should account for 80% of the area between the parallel lines in the figure. This guarantees that if the chip has a movement offset when passing the welding furnace, the chips can be pulled back to its original position by the welding pull. The solder should be made as thin as possible to ensure that the solder does not flow to other areas when the chip is mounted. Regarding the pin soldering area of the chip, the stencil opening should not exceed the width of the pad at the bottom of the chip.
Shown in photo: Stencil Welding Photo (Stencil is a tool used in PCB solder coating)
PCB reflow soldering at 183oC for about 60 seconds and the peak temperature should not exceed 205oC. Exceeding the temperature causes melting of the internal solder joint of WanTcom MMIC and damages to the chip index. Please refer to WanTcom process documents AN-109 for more details on temperature control.