This article covers two practical topics for DEK solder paste stencil printers: a step-by-step method to calibrate table level and print height, and a set of engineering improvements that eliminate frequent clogs in the solvent spray mechanism used for underside stencil wiping.
1. DEK Stencil Printer Level and Print Height Calibration
1.1 Preparation
Prepare a simple calibration fixture consisting of two steel plates to sit on the conveyor rails and two feeler gauges. The gauges are used to measure the gap between support pins and the plates during leveling and height checks.
Figure 1 | Calibration fixture: two steel plates and two feeler gauges
1.2 Leveling the Rails and Setting Height
Load the 265test program and place the two steel plates on the left and right conveyor rails, as far apart as practical while still clamped securely.
Figure 2 | Calibration plates placed on both conveyor rails
On the machine’s main screen, press F8 (Maint) to enter the maintenance interface.
Figure 3 | Maint main interface
Select F6 (Diaghost) to access the diagnostic functions.
Figure 4 | Diaghost function menu
Choose RisingTable to manually control the main table’s vertical motion.
Figure 5 | RisingTable controls for main table motion
Run Home Rising Table to reference the Z-axis, then select Raise Table to Vision Height. At vision height, the support pins will contact the underside of the plates (or a PCB if one is present). This is the correct position to verify rail level and top support height.
Figure 6 | Homing and raising to vision height for rail-level checks
With the support pins under the plates, measure the gap between each pin and the plate using the feeler gauges. A gap of 0.075 should pass through while 0.125 should not. Adjust the rail/height screws that bear against the rails until all four corners meet this requirement and are consistent.
Figure 7 | Feeler gauge check of support pin-to-plate gap on all four corners
After adjusting the height screws, the stencil print height reference can shift. In the table control interface, raise the table step-by-step from lower to higher positions until it reaches print height. Select Set Reference Print Height to display the current Z value. If the value does not meet your print process requirement, enter the desired value and press Move to drive the table to that height. Once confirmed, press Set Height to store this as the new reference print height.
Figure 8 | Set Reference Print Height dialog and move-to-height operation
Finally, lower the table from high to low positions in sequence back to zero to complete the calibration procedure.
Figure 9 | Return the table to zero to finish calibration
1.3 Why Level and Height Matter
Proper rail level and accurate print height are critical to solder paste print quality. If the table is not level, squeegee pressure will vary across the stencil, leading to inconsistent paste roll, insufficient fill in fine apertures, and uneven deposits. An incorrect print height changes the stencil-to-board gap and can cause bridging, slumping, or insufficient transfer. The feeler-gauge method verifies that the support system presents a flat, consistent datum to the PCB across the full print area, while the print-height reference ensures the machine applies the intended squeegee force and gap settings cycle after cycle.
2. Improving DEK Solvent Spray Performance for Underside Wiping
The original DEK solvent spray bar used for underside stencil cleaning can frequently clog, resulting in incomplete cleaning and subsequent insufficient paste deposits. A root-cause analysis identifies the main contributors and points to specific design and maintenance changes that eliminate the problem and reduce downtime.
2.1 Clogging Causes
- Foreign matter in the solvent tank.
- Lint and debris from the wiping paper after the vacuum stroke in the W/V/D cycle.
- Solder powder adhering to the spray head and flowing back into the orifices.
2.2 Countermeasures and Engineering Changes
1) Foreign matter in the solvent tank
Very fine particles can enter the tank when adding solvent, especially around the tank cap area. Even small contaminants can accumulate in the spray manifold and block fine orifices.
- Use a funnel when filling the solvent tank to prevent contamination.
- Add an inline filter at the tank outlet to capture particulates before they reach the spray head.
2) Lint and debris after the vacuum wipe
The current underside-cleaning sequence is W/V/D (Wet/Vacuum/Dry) using an integrated module. Lint from the wiping paper can be dislodged by the vacuum and fall onto the spray head, where it blocks nozzles. Reassess the wiping paper and switch to a higher-grade, low-lint material to reduce or eliminate debris deposition on the spray bar.
3) Solder powder adhering to the spray head
This is the most frequent cause. The spray head has a groove between adjacent spray orifices. After spraying, solder powder adheres to the head and can wick along the groove, flowing back into the orifices. When the line stops and the wiping mechanism is idle, this residue dries and hardens, resulting in blocked nozzles.
One common remedy is to mechanically punch through the clogged holes with a tool or jig. However, if the tool does not match the orifice precisely, the hole can enlarge and spray uniformity suffers.
4) Design modification: removable, raised nozzles
To address clogging at the root, modify the solvent spray bar so that each spray orifice is an individually removable nozzle insert, and raise the nozzle outlet above the inter-orifice groove. The raised outlet prevents solvent and solder paste residue from flowing back into the orifices. If a nozzle does clog, it can be removed and cleared easily with ultrasonic cleaning, restoring the original diameter and spray distribution without risk of hole enlargement.
2.3 Process Impact
These measures prevent frequent spray-bar clogging, keep the W/V/D cycle effective, and ensure consistent under-stencil cleaning. Reliable solvent delivery is essential for removing paste bridges and fines at the stencil underside, especially for fine-pitch apertures and small chip components where any residual contamination can lead to insufficient deposits, opens, or solder balls. Maintaining clean, dimensionally correct nozzles preserves the spray pattern and coverage uniformity across the stencil width, reduces unplanned downtime for manual cleaning, and avoids print quality drift associated with partial blockages.
Combined with proper machine leveling and print height calibration, the solvent spray improvements stabilize paste transfer and make the print process more robust across product changeovers and extended production runs.
