SIPAD boards are shipped with protective paper to preserve the tacky finish. Shelf life is guaranteed for 6 months.
How does SIPAD ssd work?
There are many methods used to place and fuse SMD components to one or both sides of a printed circuit board. Most concentrate on the high volume through put needed once the product has been prototyped and tested at the development level. But what about the methods used to assemble prototype quantities, usually in the lab or at small contract manufacturers specializing in small runs. Solid Solder Deposit (SSD) is a reliable solution to many of the challenges facing this segment of the cycle often overlooked.
SIPAD uses the solder mask to define each surface mount land. Solder paste is stencil printed onto the pads using a normal stencil printing operation. After a sufficient amount of paste is applied, the printed circuit board is subjected to a standard reflow without the components.
During this initial reflow, the solder paste is fused and the SIPAD ssd is formed with a meniscus above the plane of the solder mask.
At this point the boards are thoroughly washed to remove any solder residue. Because there are no components cleaning is much more efficient.
After washing, the boards are placed into a flattening system, which re-heats the solid solder deposit then flattens the pads between the platens of a cold press. This process freezes the solder deposits into a flat solid solder deposit.
Once the SIPAD board is flattened, the stencil is used to apply adhesive no clean flux to the surface mount pads. This flux is designed to be dried overnight to a super tacky finish. The solder underneath is solid so it cannot be smeared.
The finished board is then protected by a release paper to maintain the tackiness of the flux. During final assembly, the adhesive flux holds the components securely in place. The adhesive flux burns off during reflow leaving no noticeable residue.
How much does SIPAD cost?
SIPAD solid solder deposit (ssd) charges are not influenced by layer counts.
One or two side SIPAD application
Images per panel/array
Type of solder paste specified
Size of printed circuit board
Quantity and Delivery
What kind of solder paste can be used with SIPAD?
SIPAD ssd used only water soluble solder paste, eutectic or lead free, so that residues left behind after reflow can be cleaned prior to the flattening process.
How do parts stay in place during the assembly process?
Once the SIPAD ssd's are flattened, no clean adhesive flux is applied to the pad surfaces using the same stencil used to apply the paste. Because the flux is only applied to the pad surfaces, it burns off very efficiently and any residue left behind is no clean.
The standard SIPAD ssd adhesive flux is designed to be dried to a final tacky finish. Other adhesive flux products exist including water soluble versions however, these are not designed to be dried or left on the ssd's so these flux types must be applied by the assembler just prior to placement.
How thick is the SIPAD ssd?
SIPAD ssd is normally between .002 - .003 thick on .020 - .025 pitch. Thickness can vary depending on design.
What is the shelf life for a SIPAD board?
SIPAD ssd is normally provided with no clean adhesive flux. This flux is guaranteed for 6 months although many instances of boards remaining tacky for 18 months have been documented.
Example: CEM A had 30 boards processed with SIPAD ssd. The pick and place was short 11 feeders so some hand placement was required after placement. The end user wanted to test 3 units prior to the balance being finished.
All 30 boards were processed through pick and place. 3 boards were completed through hand assembly while 27 were placed un-reflowed into a sealed box to keep them clean. After the initial 3 were burned in and approved, the customer released the balance of 27 boards. These boards, after 10 days without the paper, were still tacky and soldered perfectly.
How are SIPAD boards assembled?
Assembling single sided SIPAD boards
SIPAD solid solder deposit (ssd) boards are easy to assemble without using a stencil. SIPAD boards come with the solder on the surface mount pads in a solid form that cannot smear or smudge. The pads are flat and coated with a no clean flux that is tackier than solder paste, holding the components in place during the final reflow of the assembly. SIPAD board components can be placed using standard pick and place equipment or by hand with perfect results. The flux coating buns off very efficiently leaving very little residue. Because the solder paste has been fused into solid solder, instances of solder balling, spattering and smearing are eliminated.
Assembling double sided SIPAD boards
Method 1: Hand soldering side 1, reflow soldering side 2
Many printed circuit board designs place the passive components, capacitors, resistors, and smd connectors on the bottom side of the board with the more difficult active components, QFP's, BGA's, etc, on the top side. With fluxed SIPAD ssd on both sides it is very easy to place and solder the passives on the bottom side by hand using standard soldering tools such as irons or hot air.
Traditional hand soldering requires 3 hands. One for the part, one for the heat, and a third hand for the solder. Because the SIPAD ssd board has the solder and tacky flux already in place it is the throughput and reliability of hand soldering is greatly improved.
Parts can be placed into the adhesive flux and held securely while the heat is applied (pin point hot air preferred) securing the leads in place when the ssd returns to its original pre-flattened shape. Once this side is completed the boards can be turned over, paper removed from the second side, and parts placed by hand or automatic pick and place equipment, then reflowed as usual. Bottom side components will be held in place with surface tension during this reflow cycle.
Method 2: 2 sided SIPAD, customer applied flux on second side
One method for 2 sided 2 pass reflow is possible requires that the assembler apply the flux to the second side prior to component placement and reflow. Applying flux to the SIPAD ssd surface is much easier that applying the solder paste. Most hand press printers work fine for flux application.
To facilitate 2 pass reflow, SIPAD ssd is applied to both sides of the board with flux only applied to the first side to be soldered. By lowing the temperature of the bottom side profile during the first reflow cycle, the bottom side (side 2) will remain flat because there is no flux in the solder.
It is only necessary to re-heat the assembly to attach the components. An infrared reflow has shown to be more effective than forced convection due the ability to create a delta between the top and bottom side heaters. An insulating barrier is recommended to help keep the heat off of the bottom side during the first pass reflow. During the heating of the first side it is possible that the second side pads may show signs of doming, slightly returning to their round shape. This does not affect the soldering on the second side as long as it is kept to a minimum and placement is accurate.
Once the top side is soldered, the boards are turned over, flux applied to the second side using the stencil shipped with the boards. SIPAD Systems supplies boards with Avantec adhesive flux which increases its tackiness if it is dried 12-24 hours in a controlled environment, normally 70 degrees Fahrenheit. Immediate placement is possible if time does not allow for the drying cycle. Once the flux is applied, the parts should be placed and reflowed using a standard reflow profile. Bottom side parts are normally held in place by surface tension just as in standard 2 pass reflow processes.
What about BGA?
BGA's and other blind leaded components are some of the most difficult challenges facing companies today. SIPAD ssd has proven to be one of the most economical, predictable, and repeatable method for attaching BGA's at many quantities and technology levels.
What reflow profile should be used with SIPAD ssd?
Reflow profiles are designed to control the fusing of the individual alloys that make up the "wet" solder paste. Fluxes and carriers must be burned off at a controlled rate to achieve a well blended fused alloy (solder) without spattering, solder balling or voiding.
SIPAD boards do not require such a controlled reflow profile. Because the alloys have already been fused, the final assembly need only to reheat the boards to the melting point of the solid solder deposits to get the solder to reflow. SIPAD assembly is re-heating solid solder, similar to using a solder coil and soldering iron. Solder balls, spattering are eliminated for the final assembler. In addition, voiding has been proven to be greatly reduced in all solder joints. More Info
Contact SIPAD Systems for data sheets on the solder paste for your application.