Weller WQB2000 User Manual
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NOTE:
The down stop may have to be adjusted so that the vacuum cup just comes in contact with the components top surface while
allowing the nozzle to be positioned correctly. For BGAs this position will be against the circuit board surface. For QFPs th e
correct nozzle position is approximately .04" (1 mm) above the components upper surface.
Once you have tested all features of the WQB2000 and are satisfied that the features are working properly, we recommend that you try alignment
and placement of components with the clear test boards and components provided in the Training Kit. After becoming familiar wit h the alignment
and placement procedures you be ready to practice the solder paste stenciling and reflow procedures on the copper test boards.
ALIGNMENT TOOLS AND METHODS
REGISTRATION PINS
The registration pins are designed to be secured on the machine table so that the PC boards can be placed and removed with a very high degree
of precision.
The WQB2000 comes with 3 sets of standoff registration pins (see Figure 2) and 3 sets of standard registration pins (used if only solder paste
stenciling and component placing for off-machine reflow). The standoff registration pins are needed to keep the circuit board from coming in
direct contact with the heater plate during the reflow cycle and to allow the machine to handle circuit boards with components on the bottom of
the board.
The sizes provided should fit most PC board tooling holes. In case you are working with a board that has different size tool holes, please call
Weller Customer Service Department at (843) 537-5167 to order the specific size(s) you need. Note: Special registration pins are made to order
and will require extra time. An alternate approach is to enlarge the PCB holes to one of the standard sizes provided by reaming to a +.0005"/-
.0000" tolerance.
A
LIGNMENT TEMPLATES
Two alignment template and solder paste stencil sets are included with the WQB2000 for test and training.
The templates are designed to be secured to a bare PC board with the tape provided. You will notice that the templates have a pattern of holes
that match the component leads, some holes (see Figure 4) are actually through holes in certain pad locations. These through holes are used
to align the template to the board pads. The remaining holes are depressions that are used to align all component leads (or BGA balls) with the
PCB pads. The depressions provide a positive method of locating the component in the template and will prevent accidental movement of the
component prior to its being picked off the template. Additional templates are available, consult with your distributor or the Weller factory.
Additionally, the templates have bent up tabs on all sides; these tabs serve two functions:
1.
The large tabs are used to engage with mating notches on the printing stencil and align the stencil (see Figures 3 and 4) with the PCB
pattern.
2.
The smaller tabs, along with the large tabs, are used for nozzle alignment.
ALIGNMENT METHOD - NOZZLE TO CIRCUIT BOARD
1.
Select the BGA template cut a piece of Kapton
®
tape long enough to span the template. Place tape across template perpendicularly to the
tape shelves (see Figure 3) press tape onto one side of template, pull tape taunt and press to opposite side of template. Press tape
down onto tape shelves and trim to edge of shelves with knife blade. The adhesive side of the tape should be above the lower surface
of the template. When the template is placed on the test board, it can be easily slid around without the tape adhering to the board.
NOTE:
Kapton
®
tape leaves not adhesive on the tabletop or circuit board when removed and will withstand soldering temperatures.
Acetone will remove any adhesive left by regular tape but we strongly recommend using Kapton
®
tape only.
2.
Select the clear test board without adhesive or a green test board. Position template over a BGA pattern, align the through holes with the
pads (see Figures 4 and 5) until pads are visible and centered in all the through holes, the corner holes of the template are larger then
the rest to help with alignment. Position as accurately as possible, use magnification if necessary. When all pads are aligned, touch tape
lightly in middle of opening to fasten tape to board. Adjust alignment if necessary and then press tape to board to lock template to circuit
board.
HINT:
Position the template so that the tape shelves are parallel to the sides of the WQB2000 tabletop. This will align the stencil in the
best position for applying solder paste.
3.
Place the .156 diameter standoff registration pins into two of the tooling holes of the test board. A set of spacer blocks and standoff
spacer pins are provided. Use these to support the board as necessary to keep it level with tabletop. Move the hot air nozzle to the
center of the table by moving the horizontal slide to right hand position. Place the board on the table top, adjusting its position so that the
nozzle is centered over the template.
Note:
You will find that some boards will not use standard size tooling holes, or holes will be plated. In some cases, the holes will be
of the proper size but will be very tight. A drill of the proper size can be used to ream out the hole. Plated holes can have
solder in them and are therefore not uniform (some manufacturers plate them as grounding point). If you have difficulty in
achieving good pin registration, try a smaller pin and pull them tight to the sides. Use a minimum of four (4) pins pulled tight (but
not too tight) at 45 degree angle to achieve the best results. You may also be able to use three (3) or more pins and locate the
circuit board by edge referencing, although this is the least accurate method of registration.
4.
Lower the nozzle and position it using the six (6) location tabs, adjust board position for best fit. With the nozzle in the down position,
tape the registration pin plates in place with the Kapton
®
tape provided. Raise the nozzle and remove the board. Apply additional tape in
front of the registration pins as well as behind the pins (see Figure 5).