Printed Board Type: R/F/C
Skill Level: Expert
Conformance Level: High
Revision: D
Revision Date: Jul 7, 2000
Outline
This procedure covers the general guidelines for through
hole component soldering using a solder fountain system.
There is basically only one style of through hole component.
Whether there are a few leads or many or whether the
component is large or small the component removal principles
using this method are the same.
CAUTION - Operator
Safety
This process uses molten solder
and exposes the untrained operator to serious hazards.
A thorough review of the equipment manual and comprehensive
training are mandatory. Daily maintenance is essential.
Consult the equipment manual for more information.
CAUTION - Component
Sensitivity
This method may subject the component to extreme temperatures.
Evaluate the component's tolerance to heat prior to
using this method.
CAUTION - Circuit
Board Sensitivity
PC Boards are made from a great variety of materials.
When subjected to the high temperatures of the molten
solder used in this method they are susceptible to the
following types of damage:
1. Layer delamination.
2. Copper delamination, separation of pads, barrels
of inner layers.
3. Burns and solder mask chipping.
4. Warp.
Each circuit board must be treated individually and
scrutinized carefully for its reaction to heat. If a
series of circuit boards are to be reworked, the first
several should be fully protected until a reliable procedure
is established.
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Acceptability
References |
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IPC-A-610 |
5.0 |
Component Installation |
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IPC-A-610 |
6.0 |
Soldering |
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Through Hole Component
Figure 1:
Typical solder fountain system.
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Tools and Materials
Cleaner
Extractor/Insertion Tools
Flexible Mask
Flux
Microscope
Oven
Solder
Solder Fountain System
Soldering Iron with Tips
Tape, Kapton
Wipes
Solder Fountain System
Most solder fountain systems have the same basic components.
A solder pump and solder reservoir, various nozzle sizes, controls
for solder flow height, solder temperature and timers.
Solder from the reservoir is driven up through the nozzle by
the pump. Nozzles are made of steel with welded seams and connections.
It is important that the nozzle construction allow for the capture
of the pump's inflow and for the runoff of the solder. This
prevents the excess splashing and maintains a usable solder
level above the nozzle lip.
Occasionally the opening in the solder fountain table needs
to be restricted to prevent solder splash from contaminating
the un-worked part of the board. Do not close the opening too
tight or you may impede the nozzle run off.
Above the solder fountain head there is generally a light projected
alignment mark that permits you to center the part to be removed
over the nozzle.
Solder Height Adjustment
Solder height should be set at 1.50 mm - 3.00 mm (.060" - .120")
above the lip of the nozzle. The ideal situation is to have
the leads of a component just immersed and wetted without having
the wave exert any upward pressure on the circuit board. The
solder fountain table surface should be parallel to the nozzle
surface. Components and leads on the bottom side of the circuit
board may cause the PC board to be uneven, this condition must
be compensated for.
Insufficient immersion will prevent proper heat transfer and
reflow. Excess pressure will cause solder to surge up through
holes and to spill out onto the top side of the circuit board.
Solder Temperature Adjustment
Solder temperature adjustment varies depending on several factors.
The normal setting is 260°C (500° F). During heavy use, solder
temperature may cycle between 250°C - 270°C (480°F - 520° F).
The heaters should react quickly to normal drops in temperature.
The heaters may overshoot the preset temperature when vigorous
activity is suddenly halted. Operators must be alert to temperature
fluctuations that exceed preset standards.
Solder Fountain Time Adjustment
This adjustment can be used to precisely control operations
of a repetitive nature or in instances where you want to strictly
control a circuit board's exposure to the solder fountain heat.
The timer may also be set to maximum and the on/off action of
the wave is controlled by the motor's on/off foot pedal or by
lifting the board on and off the wave.
Extractor/Insertion Tool
There are a variety of tools to help extract and/or insert the
component once reflow has been achieved. The extractor/insertion
tool should provide the operator a good grip but should not
unduly damage the component during removal or insertion
PC Board Pre-heat
Recommendations for pre-heat range from 1 to 4 hours at 65°C
- 120°C ( 150°F - 250°F). The requirements of temperature and
time for pre-heat depend on the board construction, age and
exposure to the atmosphere.
In general terms the pre-heat will serve four purposes.
| 1. |
To drive out volatiles or moisture from the circuit
board. Moisture that has penetrated the board may cause
expansion or delamination when it is rapidly heated.
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| 2. |
To prevent thermal shock to the board. Ambient temperature
in buildings in the winter can be as low as 13°C (55°F).
As the circuit board at this temperature comes in contact
with molten solder, the extreme shock of the widely
varying temperature may cause surface or internal damage.
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| 3. |
Pre-heat may permit you to pre expand the circuit board.
Some circuit boards expand so severely at the point
of high heat that they will bow up or down enough to
create difficulties in maintaining proper board profile
to the solder wave.
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| 4. |
Pre-heat raises the temperature of the circuit board
and the component to be removed. This allows for quicker
component removal. This reduces the potential for burning
of solder mask and the circuit board surface and reduces
potential for other thermal damage.
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Procedure - Circuit Board Preparation
The area surrounding the component to be removed may need protection.
If components or the circuit board surface are susceptible to
damage or exposure to solder they may be protected by using
the following procedure:
| 1. |
Straighten any leads that may prevent the easy removal
of the part.
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| 2. |
Apply Kapton tape to any flat surfaces surrounding the
rework area to insulate the surface from extreme temperatures.
Or apply high temperature flexible mask to protect irregular
surfaces. The mask may need baking to provide the proper
cure prior to reflow.
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| 3. |
Select an extractor tool and check the fit to be sure
the component can be grabbed easily.
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Procedure - Circuit Board Pre-heat
PC Boards returned from the field or where they have been exposed
to moisture for some time.
| 1. |
Bake for 4 hours at approximately 75°C (165°F). Prior
to part removal the circuit board should be pre-heated
for one hour prior to removal of the part. If possible
perform reflow immediately upon removal of the circuit
board from the oven after completion of the baking cycle.
If the circuit board must sit between the pre-heat and
removal, it may sit for the maximum of one night only
in a dry atmosphere.
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| 2. |
Top heat during removal is only used when working with
the most difficult components. To apply top heat, a
heat gun is positioned directly above the solder nozzle
at a set distance above the circuit board surface. Top
heat is applied for a set time prior to activating the
solder fountain. Heat sensitive chalk applied to the
component will signal when the proper temperature has
been achieved.
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Procedure - Installation Process
| 1. |
Preform component leads if needed, and test on a practice
board to be sure leads are properly aligned.
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| 2. |
If the holes in the circuit board are clear, insert
the component. If needed, secure in place by bending
leads or other mechanical means.
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| 3. |
Turn on the solder fountain system and allow the solder
to reach the proper operating temperature. Clean the
machine as needed and test run the pump to be sure there
is no buildup of contamination that may cause a drag
on the pumping system.
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| 4. |
Select the proper nozzle and place it into the bath
of the solder fountain system. A nozzle that is too
large will expose the circuit board surface to unnecessary
heat. A nozzle that is too small may not reflow all
the component leads.
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| 5. |
Check the table height and solder wave height to be
sure they are properly set for the circuit board to
be worked on.
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| 6. |
Apply liquid flux to all the solder filled holes or
to the component leads if the component has been inserted
into open holes. Apply the flux to both the top and
bottom side.
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| 7. |
Place the circuit board over the nozzle. Check the position
using the alignment light.
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| 8. |
Activate the solder fountain. Once full solder reflow
has been achieved insert the component, if not already
in place. A great deal of operator skill and experience
are required to expect good results when inserting the
component during the solder fountain cycle.
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| 9. |
Immediately drop the solder fountain wave to prevent
over exposure.
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| 10. |
Allow the circuit board to cool before handling and
inspection.
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| 11. |
Clean the area and inspect for signs of damage. |
