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PREHEATING
Preheating of a printed circuit assembly is normally required in the repair process whenever any one or more of
the following situations exist.
1. Epoxy glass substrate with 4 or more layers.
2. Substrate with large ground planes.
3. Substrate of ceramic, polyimide or other high heat dissipative material.
4. Printed circuit assembly with large metal heat sinks.
Preheating of assemblies such as those listed above will accomplish the following objectives.
1. Minimize thermal shock by elevating the assembly temperature to a level closer to solder melt
temperature.
2. Minimize the heat cycle reflow time.
3. Overcome the heat dissipation characteristics of the assembly.
4. Minimize adjacent melts on densely populated assemblies.
The assembly undergoing repair must be heated for a length of time sufficient to saturate at the preheat
temperature required. The PCB preheat temperature normally used is 100°C (212°F) for epoxy glass substrates
and 120°C (248°F) for ceramics and polyimides.
Although many different methods such as ovens and preheated plates may be utilized to accomplish the required
results, the user must employ a method which heats the assembly as evenly as possible and can be employed with
the ThermoFlo unit. The preheat temperature should also be maintained throughout the Removal/Replacement
process. PACE recommends the use of its Heat Wave (HS 200) system for this purpose.
PRC 1500 SYSTEM
The PRC 1500 (or PRC 1500E) system combines the versatility of PACE's MBT 250A (or MBT 250AE) with the
expandability of the Programmable ThermoFlo. All the conductive handpieces and accessories that are included
with the MBT 250A (or MBT 250AE) and all the accessories that are included with the ThermoFlo Unit are
provided with the PRC 1500 (or PRC 1500AE). This pair gives you virtually unlimited capabilities for
production or rework of any thru-hole, surface mount or mixed technology printed circuit board.
GENERAL PROCESS GUIDELINES
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