In another embodiment of the disclosure, a method of producing solder joints may employ applying a low temperature solder paste, such as a tin-bismuth alloy (e.g., SN42BI58), to a printed circuit board (“PCB”) to form solder deposits, and selectively placing higher temperature preforms, such as SAC305 preforms, in the solder paste deposits. Thus, a region of the board contains low temperature solder (for example Sn55Bi45 or Sn60Bi40), which can be used in a second solder process at a reflow temperature that does not disturb the SAC solder joints (for example reflow at 200° C.).
Low temperature solder joints are instead created by printing just one type of solder paste (for example SAC305) and then by selective pick and place of low temperature preforms (for example Sn42Bi58) into the SAC paste, and reflowing the board at SAC temperatures (for example about 240° C.). Methods and approaches in accordance with one or more embodiments beneficially do not require any sophisticated assembly operation, such as dispensing low temperature solder paste which is inefficient, to create a second, low temperature region on the PCB.
ALPHA SOLDER PREFORMS VERIFICATION
A second soldering operation can then be performed on the PCB (solder a radio frequency or RF shield, for example) after electrical verification testing, without disturbing the SAC solder joints.
ALPHA SOLDER PREFORMS FREE
In accordance with one or more embodiments, a portion of one side of a PCB may be selectively created with low temperature solder coexisting with standard lead free SAC solder. The solder joint of claim 15, wherein the reflow temperature of the solder joint is between 190-200° C. The method of claim 10, wherein the reflow temperature of the solder joint is between 190-200° C.Ĥ9-53% by weight tin 0-1.0% by weight silver 0-0.1% by weight copper and balance bismuth.ġ6. The method of claim 11, wherein the composition further consists of silver.ġ4. The method of claim 11, wherein the composition consists of 42% by weight tin and 58% by weight bismuth.ġ3. The method of claim 10, wherein the low temperature solder paste is a composition consisting of tin and bismuth.ġ2. Applying low temperature solder paste to an electronic substrate to form a solder paste deposit placing a high temperature preform in the solder paste deposit and processing the electronic substrate at a reflow temperature that is appropriate for the low temperature solder paste to create a low temperature solder joint resulting from a dissolution of the high temperature solder preform into the low temperature solder paste deposit.ġ1.
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