Desoldering of LQFP128 Components to be Reused in the EFSOT Verification Board

Several Philips LQFP128 components have been recovered from EFSOT lead-free solder Test Boards, sent to Gaiker by Philips and Thomson. These components have been delivered again in appropriate trays to the source, and after a validation they will be assembled as a reused device on the EFSOT Verification Board. Different units of EFSOT Test Boards have been received at Gaiker facilities: 20 units from Philips and 18 units from Thomson (two different laminates can be identified due to different colour). This boards are shown in Figures 16 and 17.


Figure 16. Thomson boards type 1 and 2.


Figure 17. Philips board

Taking into account the previous research done and the results obtained, the de-soldering procedure based on hot air has been used to recover the LQFP128 component. In order to reduce de-soldering time and to minimise physical damages in packages and connection leads (alignment and coplanarity), the most important factors are as follows:

• Hot air must be focussed directly on the connection leads (avoid subjecting the component to high temperatures).

• Hot air must be distributed homogeneously. All leads must be de-soldered at the same time in order to reduce the risk of loss of coplanarity and alignment when the component is recovered.

According to this important points, a specific desoldering nozzle for this component has been designed and manufactured by GAIKER with the following features:

• The design allows a better protection of the component from the high temperatures required to re-melt lead-free solders.

• The hot air flow is guided over all connection pins at the same time, instead of the package. This is possible thanks to internal cavities that avoids preferential ways for the air.

• Homogeneous distribution of the hot air over the four sides of the component. Less risk of damage in leads.

• The vacuum extractor is included in the nozzle.

• Nozzle dimensions matches with the component dimensions (for other components and sizes different nozzles are needed). The dimensions of LQFP128 component are shown in Figure 18.

• Made of aluminium

Figure 18. Component dimensions

The design and the real nozzle can be seen in Figure 19. The nozzle has been installed at a de-soldering prototype (Figure 20) that includes a platform adjustable to position the board in the right place, hot air and vacuum supplier. Once the system was ready to operate some initial tests were required to optimise the system and to determinate the de-soldering conditions for this specific component (air temperature, flow parameter, distance between the component and the nozzle and time):

• Average de-soldering time 90s. After this time the solder is supposed melted. For a similar component from a lead-containing PCB the time has been 50s.

• Hot air temperature: 450ºC

• Distance from the nozzle: 3 mm

• Flow parameter: 10

Once the system was ready, all the components were de-soldered from the EFSOT Test Board and the results are shown in Table 8. Some problems have been found de-soldering the components of some Thomson Test Boards:

• In general, time has been longer.

• Part of the board circuit remained joint to some component pins and thus, it was removed from the laminate.

The de-soldered LQFP128 components in specific trays have been sent to Philips for validation and later re-assembling in the Verification Boards.


Table 8. Results of the LQFP128 components desoldering.

 Validation of the recovered components [next chapter]