Solder Pot Maintenance and Dross Control
A wave solder pot is a bath of molten alloy that is used continuously, and both the alloy and the equipment change while it is in service. Maintenance is the discipline that keeps the change inside the limits the process was qualified with.
How Dross Forms
Dross is oxide that forms where the molten alloy meets the air, and the wave surface produces a large area of contact. The rate depends on the temperature, the agitation and the atmosphere.
A higher temperature produces dross faster and consumes alloy. Our wave profile notes describe the temperature that is used.
Removing Dross Without Removing Alloy
Dross is removed with a paddle and a skimmer, and the operation inevitably takes some good alloy with it. The removal should be done at the lowest practical temperature and the loss should be recorded.
The dross rate is a useful indicator of the pot condition. Our floor control notes describe how the record is kept.
Contamination and Alloy Analysis
Copper, iron, gold and flux residues accumulate in the pot, and each affects the alloy differently. Copper raises the liquidus and produces a slushy solder; other metals can affect the joint appearance.
The alloy should be analysed at a stated interval and the result compared with the specification. Our joint criteria notes describe the acceptance that follows.
Wetting and Its Symptoms
The first sign of a contaminated pot is usually a change in wetting rather than a visible defect. A joint that fills less well than it did is a signal to analyse the alloy before adjusting the profile.
Adjusting the profile to compensate masks the cause. Our solderability notes describe the test that separates the two.
Nozzle and Pump Condition
The wave shape is set by the nozzle and the pump, and both wear. A wave that is lower or less stable than it was produces a different contact time for the same setting.
The wave height should be measured against a reference. Our wave notes describe where it is measured.
Records and Replacement
The pot record should carry the alloy specification, the analysis results, the dross removal dates, the topping up and the nozzle changes. That record is what allows a change in joint quality to be explained.
Our quality notes describe how the records are kept.
Verification
The verification is an alloy analysis at a stated interval compared against the specification, a wave height measured against a reference, and a solderability check on a sample board after any topping up.
Our first pass yield notes describe how the results are used.
Process Control and Verification
On a design of this kind, alloy analysis is the item that decides how the rest of the board is arranged. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.
Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end. Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule.
The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.
Process Control and Verification
On a design of this kind, alloy analysis is the item that decides how the rest of the board is arranged. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.
Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage. Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch.
Process Control and Verification
On a design of this kind, alloy analysis is the item that decides how the rest of the board is arranged. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design.
Process Control and Verification
On a design of this kind, alloy analysis is the item that decides how the rest of the board is arranged. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.
A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.
Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.
FAQ
Can the pot be topped up indefinitely? No. Topping up dilutes the contaminants but does not remove them, so the analysis interval is what actually controls the alloy.
Does a nitrogen blanket remove the need to remove dross? It reduces the rate at which dross forms. It does not eliminate the removal step.
What does gopcb provide for wave solder maintenance? We provide an alloy analysis at a stated interval against a written specification, dross removal at the lowest practical temperature with the loss recorded, wave height measured against a reference, nozzle and pump changes recorded, and a solderability check on a sample board after every topping up.
