LEV CHEK
Solder Wave Gauge

What is LEV CHEK?
The LEV CHEK Solder Wave Gauge is a custom tempered glass panel made similar in size and shape to a printed circuit board and is designed to be used on wave soldering equipment to monitor flux coverage, wave shape, wave turbulence, leveling of the conveyor and other soldering quality factors. Heat resistant gauge markings are printed on the top surface of the LEV CHEK glass in 1/2" or 1" grid patterns. The tempered glass is designed for normal wave soldering temperatures. When used according to the recommended procedure, LEV CHEK glass will not break from the heat of the molten solder. Flatness of this precision gauge is essential to its function. The gauge surface is held to a flatness tolerance of 0.0003 inch per linear inch.

Looking through the LEV CHEK over the solder wave

Why it is needed
The need for a process control gauge such as LEV CHEK is indicated by the many variable factors which control the actual contact of solder on the working surface of the circuit board being soldered. Consistent, measurable wave contact of solder to the board is assured through the use of this gauge. Diagnostic observations through the clear glass reveal:

• The leveling the transport system to the solder wave
• Evaluation of smooth solder pump performance
• The adequacy of flux distribution and thickness

This unique method of topside observation of the actual "wave-to-board" contact provides added opportunity for precise analysis of your own particular process. LEV CHEK is helpful in identifying proper angle of contact, flux and/or oil intermix, displacement, flushing action, direction of solder flow, and meniscus velocity at the break away trailing edge of the solder contact. It also allows visual observation of wave impingement on board surface for skips or turbulence.

How to use
The LEV CHEK Solder Wave Gauge is easy to use. The basic principle is to simulate all conditions as close as possible to your own production process. This means fluxing, preheating, conveyor speed etc. to be kept the same as if soldering actual printed circuit boards. Simulating these conditions will demonstrate visibly how your process works. Place glass with grid pattern side facing up.

• Flux Application
  Visual observation of the pattern of the flux wave or foam head through the transparent LEV CHEK gauge monitors adequate, uniform quantity of flux application. Subsequent action of air knife or brush control can be monitored and precisely adjusted to prevent waste and fire hazard of flux spillage on preheaters.
• Preheater Effectiveness
  Can be observed for controlled evaporation of flux solvent prior to entry of gauge or pcb into hot solder wave.

Evaluation of the solder wave

• Dynamic Test
  A fast "qualitative" method performed by simply running the LEV CHEK gauge across the entire soldering operation at the same continuous rate as a standard production pcb. Observe uniformity of solder sweep across entire width of contact surface. The total area of glass contacted by the solder wave illustrates the immersion depth of the board in the solder. Trailing edge at break away of solder from gauge should show a minimum of 1/32" of flux line - a good indicator for reducing tendency for icicling. The velocity of meniscus of solder draining should be greater than velocity of the board over the solder machine. Simple observation will allow swift adjustment of conveyor speed or wave height. The "float effect" due to impingement action of solder wave and thermal gradient produced on the board can be observed and controlled by fixture adjustment, conveyor speed and temperature of solder.
• Stationary Test
  Achieved by stopping the conveyor with the LEV CHEK gauge centred across the solder wave within the marked gauge lines. This test is "quantitative" as now the precise contour can be seen as well as the total area of contact with the solder. If the width of the wave is not uniform at each end as lined up by the gauge lines as seen in the figure below, then leveling adjustments may be made while the LEV CHEK gauge is still in place.

  

  To determine contact time, place gauge on conveyor using normal speed. Measure width of wave as glass is centered on solder. Conveyor may be stopped briefly to obtain width. Contact time and the resulting time/temperature ratio can be calculated by dividing the thickness of wave observed on gauge by the conveyor speed. See example of contact time calculation below:
  
  3 inch contact length x 12
  ----------------------------- x 60 = 3.75 seconds contact time.
  4 ft/minute conveyor speed
  

Edge Brackets
The purpose of the edge brackets is to set the bottom of the glass plate at the same level as the bottom of the pcb (as shown in the figure below). The edge brackets are made from 0.020" titanium and are sold for a specific glass thickness (either 0.125" or 0.187") and come in sets of four to a package.

Edge Brackets - two bracket sizes are available for 1/8" and 3/16" glass thicknesses

This tempered glass panel has been designed to withstand normal heat of soldering for short duration. The glass will not tolerate thermal shock as well as a laminated epoxy glass substrate and certain precautions should be taken to prevent accidental breakage.

• Do not force the glass into a fixture or mount it too tightly. Expansion from heating may increase the risk of breakage.
• Soldering temperatures of 260-275ºC will not adversely affect the LEV CHEK.
• Normal transport speeds across preheaters are acceptable, and stationary dwell time on wave for observation is allowable for up to 30 seconds.
• Temperatures above 275ºC require extra precautions to reduce the sudden build up of uneven thermal strain on the glass. At these higher temperatures the use of a slower speed across the preheaters is suggested.
• Do not hold the glass panel stationary on the solder wave longer than thirty seconds.

When to Use
How often the LEV CHEK gauge is used depends on the degree of process control you need to satisfy your company's quality requirements. Time required for the dynamic test as a routine quality check of the wave process is not much longer than the cycle time of soldering a standard production board. This makes frequent monitoring easy and inexpensive without costly delays of production interruption.

As a general rule, the gauge should be used at the start of each shift. If many different sizes of boards are used or the wave parameters are changed an additional test is recommended.

Several standard size gauges are suitable for adjustable fixtures. If special sizes are needed for dedicated production fixtures, they may be ordered to any custom size required. A 10 piece minimum is required.

Caution

• Do not expose glass gauge to soldering heat without flux and preheat cycle.
• Do not position gauge so glass extends beyond width of solder wave. Choose gauge or wave width so that solder spreads completely across the width of the LEV CHEK gauge.
• Position LEV CHEK for use with marking side up.
• The LEV CHEK Solder Wave Gauge is tempered borosilicate glass specially designed to withstand the extreme thermal shock of a typical 275ºC solder wave. Do not try this with ordinary glass.
• Although it has good mechanical strength and excellent impact properties (five times as strong as standard annealed glass), it is sensitive to mechanical stress on the corners and edges.
• Do not force it or mount tightly in a rigid holding fixture. Expansion from heating may cause unusual mechanical stress and together with the thermal shock increase the risk of breakage.
• Because of the nature of this tempered glass, if breakage should occur, the glass may shatter completely into "gravel type" particles not needle sharp slivers like ordinary window glass. Any glass particles will float on the solder surface and are readily removed.
• Use all normal safety precautions while observing LEV CHEK including safety glasses.

Cleaning and Storage
Allow the LEV CHEK gauge to cool before handling. Because it is thicker than a production pcb, it will take more time. Do not chill the hot glass suddenly. Allow it to air cool. Clean off excess flux remaining with suitable solvent. Dry and replace glass gauge in its protective bag and envelope. Store LEV CHEK carefully. It is more likely to be broken through careless handling than from heat. Bookcase or file drawer storage is advised. Use the shipping box for convenient storage.

Test results indicate that this product is suitable for lead-free soldering, which often occurs at higher temperatures. Please evaluate in your lead-free process. The increase in temperatures that are seen with lead-free solders will have an impact on overall life of the tempered glass. These temperatures will increase the burden on the user to manage the thermodynamic aspects of the LEV CHEK use. More important are preheat temperatures and conveyor speed and the duration of any stop or dwell over the molten mass. If temperature is localised to only one section of the LEV CHEK it will definitely cause problems due to non-uniform heating.

See also!  Titanium masking and stiffening strips  Wave soldering machine fingers  Solder pots

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August 2005
Version 2.0